A Level Biology: The Structure and Function of Nucleic Acids

Deoxyribonucleic acid (DNA) and Ribonucleic acid (RNA) are perhaps the most important of all biomolecules. 

 

Why? 

 

Well, these nucleic acids contains the instructions that make every single living organism on the planet. 

 

DNA and RNA are polymers, composed of monomers called nucleotides, and it’s now been 67 years since Watson and Crick published their seminal paper proposing the molecular structure of nucleic acids in the prestigious journal ‘Nature’ on the 25th April 1953.

 

In this section entitled “The structure and function oNucleic Acids” you’ll learn about the basics of molecular genetics, beginning with the structure and function of nucleotides. From here you’ll be in a much better position to fully understand the structure and function of the most important of all biomolecules - DNA and RNA. Once you have learned all about these structures, you’ll go on to find out about the different types of RNA - in particular messenger RNA (mRNA) and transfer RNA (tRNA), which you must become very familiar since you’ll need to be able to describer the roles of each of these players in protein synthesis. To finish this section you have to learn about genes and non-coding DNA before revisiting how DNA is stored in eukaryotes, prokaryotes and the cellular organelles Mitochondria and Chloroplasts.

A Level Biology: Nucleic Acids - 

Nucleotides & Polynucleotides

 

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In this A-Level Biology Lesson "Nucleic Acids - Nucleotides and Polynucleotides" Following the Learning Outcomes you’ll learn that Nucleotides are the monomers of DNA and RNA. Nucleotides are made up from 3 “parts” - The Pentose Sugar, The Nitrogenous Bases (which can be classified as either Purines or Pyrimidines) and The Phosphate Group. You learn the Structure of a nucleotide and how Condensation Reactions Build Polynucleotides. The lesson will finish with a basic Comparison DNA and RNA.

As you’ll have learned from watching the lesson, nucleotides have three parts to them: -

 

1) A pentose sugar (5 carbon atoms in it). By convention the carbon atoms are numbered; 1’, 2', 3’ etc, read as "one prime", “two prime", 3 prime, etc. This convention allows us to distinguish each of the carbon atoms in the base. It is useful when identifying the pentose sugar and describing it to others… for example, if carbon 2' has a hydroxyl group (OH) attached, then the pentose sugar is ribose, found in RNA. However, if carbon 2' just has a hydrogen atom (H) attached, then the sugar is deoxyribose, found in DNA.

 

2) A phosphate group - which is negatively charged, and gives nucleic acids their acidic properties.

 

3) A nitrogenous base. There are five different nitrogenous bases (you don't need to remember their molecular structures), but you do need to be aware that of them contain the elements carbon, hydrogen, oxygen and nitrogen, and you’ll also need to know which are Purines and Pyrimidines. 

 

The nitrogenous bases are generally referred to by their first letters only, (but yes, you do need to learn their full names).

 

There are five nitrogenous bases: -

 

Adenine (A

Cytosine (C

Guanine (G

Thymine (T) (DNA only)

Uracil (U) (RNA only)

 

*Note: - The base thymine is only found in DNA and the base uracil is only found in RNA, so there are only four different bases present at a time in one nucleic acid molecule.

 

DNA contains - A, C, G and T

Whilst RNA contains A, C, G and U

 

It is also important to note, that informally when talking about nucleotides, we refer to them by the letter name of the nitrogenous base that makes them… for example, the nucleotide ‘A’ (contains the nitrogenous base Adenine - but this nucleotide is actually called “Adenosine” (which you’ll be familiar with from that super imprint molecule ATP (Adenosine triphosphate). 

 

When a nitrogenous base is attached to a Pentose sugar and Phosphate group, the whole molecule is called a nucleotide. So, what are the actual names of the nucleotides: - 

 

When the nitrogen’s base A (Adenine) is attached to a pentose sugar and phosphate group - you already know this nucleotide is called Adenosine.

 

When C (Cytosine) makes up the nucleotide, the nucleotide is called: Cytidine. 

 

When G (Guanine) makes up the nucleotide, the nucleotide is called: Guanosine.

 

When T (Thymine) makes up the nucleotide, the nucleotide is called: Thymidine.

 

and When U (Uracil) makes up the nucleotide, the nucleotide is called: Uridine.

It’s super useful to know this information (since you’ll no doubt read these terms in books, and even exam questions). But you already have a lot to remember and you will not be expected to use these names to answer exam questions. 

 

So why should you be aware of them?

Well learning A-level biology is all about understanding concepts, terminology and being able to apply this knowledge, and when you know the language everything becomes so much easier… 

 

For example: - now you know why ATP is called “Adenosine triphosphate”. Adenosine is the name of the nucleotide and since it has 3 phosphates its called triphosphate. 

 

In fact all nucleotides can have one, two or three phosphate groups. So for instance you can have adenosine monophosphate (AMP), adenosine diphosphate (ADP) and of course adenosine triphosphate (ATP). These nucleotides are very common in cells and have many roles other than just  being a component of nucleic acids. ATP as you’ll now by now, is used as an energy storage molecule, while AMP and GTP are used as chemical messengers.

 

What is Nucleotide Polymerisation?

 

Polymerisation is biochemical combination of monomers to form polymers, and nucleotides polymerise via condensation reactions between the 3' carbon of the sugar and an oxygen atom of the phosphate group which results in the formation of phosphodiester bonds. The phosphodiester bonds link the pentose sugar to the phosphate - resulting in the sugar-phosphate backbone. Since the nitrogenous bases do not take part in the polymerisation, the sugar-phosphate backbone is made and the nitrogenous bases extending out from it. A polynucleotide has a free phosphate group at one end, this end is called the 5' end (because the phosphate is attached to carbon 5' of the sugar), a free OH group at the other end, called the 3' end (because it's on carbon 3' of the sugar).

 

The terms 3' and 5' are often used to denote the different ends of a DNA molecule, and will be useful to know when describing how DNA replication take places, or explaining where primers bond during PCR

 

Ok, so now you know that nucleotides are super important and you’ve watched the lesson on nucleotides, completed the knowledge check PDF and read all this… it’s time to move on to learning about DNA, and a brief history of the key players involved in the “discovery” of this infamous biomolecule.

A Level Biology: Nucleic Acids - Nucleotides and Polynucleotides Revision Notes with Knowledge Check Questions and Answers pdf
A Level Biology: Nucleic Acids - Nucleotides and Polynucleotides Revision Notes Poster A3 PDF

A-Level Biology: "Nucleic Acids - Nucleotides & Polynucleotides"

 

Nucleotides are the monomers (mononucleotides) that make up Polynucleotides such as DNA and RNA.

 

Each Nucleotide is composed of 3 parts.

  1. The Pentose Sugar

  2. The Nitrogenous base (either Adenine, Thymine (DNA), Cytosine, Guanine or Uracil (RNA)

  3. The Phosphate Group (ion)

 

 

Notice Carbon number 2 of these Pentose Sugars.

  

Ribose, has an OH group at Carbon 2.

Deoxyribose, has a Hydrogen at Carbon 2.

The Nitrogenous Bases are either Purines or Pyrimidines.

Purines (A and G) have “2 Rings”

Pyrimidines (C, T and U) have only “1 ring”

The Phosphate group – Notice the OH groups, remember these are important for condensation reactions.

The basic structure of a nucleotide:

Nucleotides join to one another via Condensation Reactions.

 

An OH group - located on the Phosphate group, attached to Carbon number 5 of the Pentose Sugar, undergoes a condensation reaction with the OH group attached to Carbon Number 3 of the Pentose Sugar. This condensation reaction results in the removal of a water [H2O] molecule and the formation of a phosphodiester bond between the nucleotides. Many of these condensation reactions take place to form the Sugar-Phosphate Backbone of polynucleotides.

You also have to be able to compare and contrast DNA and RNA… These are useful points from this lesson to include in your answers…

 

DNA has the Pentose Sugar “Deoxyribose” and is made up of the Nitrogenous bases, Adenine, Thymine, Cytosine and Guanine.

RNA has the Pentose Sugar “Ribose” and is made up of the Nitrogenous bases, Adenine, Uracil, Cytosine and Guanine.

A Level Biology: Nucleic Acids - 

The Structure and Brief History of DNA

 

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In this A-Level Biology Lesson "Nucleic Acids - The Structure and Brief History of DNA"

00:00 Intro Screen / Learning Outcomes

01:30 A Super Brief History of DNA

03:09 DNA contains Purines and Pyrimidines

03:27 1950 - Chargaff's Rule

03:53 Wilkins and Franklin

04:40 1953

05:16 The DNA Nucleotide

06:03 Complementary Base Pairing requires DNA polynucleotide chains to run in Antiparallel directions...

07:30 The % of A is equal to T...

08:00 Antiparallel Structure of DNA

08:26 Hydrogen bonding...

09:14 All this leads Watson and Crick to Build their 3D model of DNA...

09:29 - Summary of DNA Structure.

A Level Biology: Nucleic Acids - The Structure and Brief History of DNA Revision Notes with Knowledge Check Questions and Answers PDF
A Level biology: Nucleic Acids - The Structure and Brief History of DNA Revision Notes Poster A3 PDF

DNA is a nucleic acid, (because it is found in the nucleus and is weakly acidic).

 

DNA is a stable polynucleotide, which means it is composed of many nucleotides and does not begin to denature until it is heated to approximately 86°C. So, DNA is much more stable than proteins! - remember many proteins begin to denature just above 40 °C.

 

DNA is long molecule and is wound around proteins called histones.

DNA is a polymer: the monomers are nucleotides.

 

Each nucleotide has three components: -

★ Sugar – deoxyribose – which is a 5-carbon sugar

Phosphate group

Nitrogenous Base – one of four nitrogen containing compounds: Adenine (A), Thymine (T), Guanine (G) or Cytosine (C).

 

The nucleotides are arranged in a double helix (a twisted ladder). The two sides of the 'ladder' are chains of alternating sugar–phosphate groups, while the ‘rungs’ of the  'ladder' are made from pairs of bases bonded together by hydrogen bonds.

 

It is important that, both for protein synthesis and DNA replication, the strands can separate and rejoin without damaging the molecule.

 

Only one part, of one strand of the DNA molecule, at any particular point in the double-stranded molecule – "the sense strand" – is used to make proteins. The other side serves to stabilise the molecule.

 

The Nitrogenous bases.

The four bases always bond (via hydrogen bonding) in the same way: –

A hydrogen bonds with T and

C hydrogen bonds to G.

 

So if you know the base sequence down one side of the DNA molecule, you know the other!

For example, if one strand reads: -

G C G C G G T A C C T A G A T A C A A A A
...then of course the the other (the complementary) side will read: -
C G C G C C A T G G A T C T A T G T T T T

Remember!

The nitrogenous bases are held together by weak hydrogen bonds, you must also remember that there are 2 hydrogen bonds between A and T (i.e. A=T) and 3 hydrogen bonds between C and G (G ≡C).

 

These regular hydrogen bonds along the whole length of the molecule make DNA very stable.

To appreciate the importance of DNA (and genes) in an organism, it is also important to understand the significance of proteins: -

  • Enzymes are proteins that affect the rate of metabolism

  • Structural proteins make up an important part of the fabric of organisms, e.g. collagen, keratin and elastin

  • Antibodies that form a vital part of the immune system are proteins

  • Hormones, e.g. insulin, are proteins

  • Proteins form channels in cell membranes that control what passes in and out of the cell

  • Blood clotting involves many different proteins in a complex sequence of reactions

  • Surface proteins on a cell are unique in each organism, which helps the immune system to differentiate self from non-self and so defend against pathogens / foreign invaders.

Organisms are largely made from proteins, and proteins play many important roles in what happens in our bodies. Yet each individual starts life as a fertilised cell; little more than two sets of genes, made from DNA.

 

So, When revising A-Level biology be sure to consider the relationship between DNA and Protein

 

for example: -

The role of nucleic acids in protein and enzyme synthesis.

How the genetic code in DNA is used to build a protein: - i.e. Transcription and Translation.

A Level Biology: Nucleic Acids - 

The Structure of RNA (mRNA, tRNA and rRNA)

 

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00:00 Intro Screen / Learning Outcomes

01:27 RNA is similar to DNA

01:56 The 3 types of RNA (mRNA, tRNA and rRNA)

02:35 RNA nucleotide

03:00 RNA Summary

03:34 Compare and Contrast DNA and RNA

04:44 Final points you need to know...

A Level biology: Nucleic Acids - The Structure of RNA (mRNA, tRNA and rRNA) Revision Notes Poster A3 PDF

The Structure of RNA.

 

RNA stands for ribonucleic acid, of which there are several types (mRNAtRNA and rRNA). These different types of RNA are also nucleic acids (like DNA), although RNA is single stranded and not always found in the nucleus...

  • Messenger RNA (mRNA) is a single, long strand of nucleotides that is a copy of a gene (transcription)

  • Transfer RNA (tRNA) is a small, cloverleaf-shaped molecule that brings particular amino acids to the ribosome during translation

  • Ribosomal RNA (rRNA) is a constituent of ribosomes.

You should be able to construct a table to show the essential differences between DNA and RNA Like this: - ​

Table to compare DNA and RNA

A Level Biology - Genetics: The Structure and Function of mRNA and tRNA

 

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Genetics: the Structure and Function of mRNA and tRNA A3 Poster PDF for A Level Biology

A Level Biology - Genetics: Genes and Non-Coding DNA

 

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Genes and non coding DNA, Define exon, intron, codon, anticodon, gene, Question A-Level Biology PDF
Genetics: Genes and Non-Coding DNA - What are Exons and inions? A3 Poster PDF for A Level Biology

Genes are sections of DNA (deoxyribonucleic acid) that code for the production of particular proteins.

 

Humans have about 20,500 genes on our 23 chromosomes. Chromosomes are basically long , coiled DNA molecules.

 

DNA has two main abilities: -

1) DNA carries genetic informationthe genetic code – from which the essential proteins are made.

2) DNA can make exact copies of itself (DNA replication), and it can be copied exactly again and again which means that, when cells divide (see the Cell Cycle and Mitosis), each new cell receives an identical copy of the genetic information in the parent cell.

These abilities make cell division possible, without which there would be no growth or reproduction.

 

All eukaryotic cells have chromosomes. Each chromosomes is a single, very long molecule of DNA 

DNA is highly coiled and folded so that it can fit into the nucleus of a cell.

 

Remember!

Each gene may come in more than one form. An alternative form of a gene is known as an allele.

For example, the gene that codes for the protein Factor 8 (a vital part of the blood-clotting mechanism) has two alleles: one that codes for the functioning protein and one faulty allele that leads to the disease of haemophilia. Haemophiliacs need injections of Factor 8 to allow their blood to clot normally.

 

The position of a particular gene on a chromosome is known as its locus. (loci - location of the gene).

 

Diploid cells have 2 sets of chromosomes

 

Haploid cells have 1 set.

 

In diploid cells the chromosomes come homologous pairs; they have the same genes at the same loci

 

It is important to remember that although homologous chromosomes carry the same genes, they may not carry the same alleles of a gene. If both alleles for a gene are the same (e.g. AA or aa), then the organism is homozygous for that gene. Remember AA = Homozygous Dominant whereas aa = Homozygous recessive. If there are different alleles of a gene on homologous chromosomes (e.g. Aa), then the organism is heterozygous for that gene.

A Level Biology - Nucleic Acids

How DNA is Stored in Eukaryotes, Prokaryotes,

Mitochondria and Chloroplasts.

 

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Cells and Organelles - How DNA is Stored in Eukaryotes, Prokaryotes, Mitochondria and Chloroplasts A3 Poster PDF for A Level Biology
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AQA Specification Reference: - 3.1.5.1 Structure of DNA and RNA. Both DNA and RNA are polymers of nucleotides. Each nucleotide is formed from a pentose, a nitrogen-containing organic base and a phosphate group: - 

• The components of a DNA nucleotide are deoxyribose, a phosphate group and one of the organic bases adenine, cytosine, guanine or thymine. 

• The components of an RNA nucleotide are ribose, a phosphate group and one of the organic bases adenine, cytosine, guanine or uracil. 

• A condensation reaction between two nucleotides forms a phosphodiester bond.

 

CIE Specification Reference: - 6 Nucleic acids and protein synthesis. 6.1 Structure and replication of

DNAa) describe the structure of nucleotides. 

 

Edexcel (Biology A – Salters-Nuffield) Specification Reference: - Topic 2: Genes and Health. 2.5 i) Know the basic structure of mononucleotides (deoxyribose or ribose linked to a phosphate and a base, including thymine, uracil, cytosine, adenine or guanine) and the structures of DNA and RNA (polynucleotides composed of mononucleotides linked through condensation reactions).

 

Edexcel (Biology B) Specification Reference: - Topic 1: Biological Molecules. 1.1 Carbohydrates ii) Know the structure of the pentose ribose (and deoxyribose).1.4 DNA and protein synthesis i) Know the structure of DNA, including the structure of the nucleotides (purines and pyrimidines), the sugar-phosphate backbone and phosphodiester bonds.

 

OCR (Biology A) Specification Reference: - Module 2: Foundations in biology – 

2.1.2 Biological molecules. (d) the ring structure of ribose as an example of a pentose monosaccharide. 2.1.3 Nucleotides and nucleic acids. (a) the structure of a nucleotide as the monomer from which nucleic acids are made. To include the differences between RNA and DNA nucleotides, the identification of the purines and pyrimidines and the type of pentose sugar. (b) the synthesis and breakdown of polynucleotides by the formation and breakage of phosphodiester bonds.

 

OCR (Biology B) Specification Reference: - 2.1.4 Nucleic acids. (a) the structure of a nucleotide as the monomer from which nucleic acids are made - To include the differences between RNA and DNA nucleotides, the identification of the purines and pyrimidinesthe type of pentose sugar and the formation of phosphodiester bonds (the sugar-phosphate backbone).

 

WJEC Specification Reference: - Basic Biochemistry and Cell Organisation (1). (c) the structure, properties and functions of carbohydrates: pentose sugars Ribose and Deoxyribose).

Basic Biochemistry and Cell Organisation (5). Nucleic acids and their functions, (a) the structure of nucleotides (pentose sugar, phosphate, organic base). (e) the structure of nucleic acids: DNA bases: purines and pyrimidines. (f) the similarities and differences in the structure of RNA and DNA

AQA Specification Reference: - 3.1.5 Nucleic acids are important information-carrying molecules. 3.1.5.1 Structure of DNA. Deoxyribonucleic acid (DNA) is an important information-carrying molecules. In all living cells, DNA holds genetic information. DNA is a polymer of nucleotides. Each nucleotide is formed from a pentose, a nitrogen containing organic base and a phosphate group. The components of a DNA nucleotide are deoxyribose, a phosphate group and one of the organic bases adenine, cytosine, guanine or thymine. A condensation reaction between two nucleotides forms a phosphodiester bond. A DNA molecule is a double helix with two polynucleotide chains held together by hydrogen bonds between specific complementary base pairs. Students should be able to appreciate that the relative simplicity of DNA led many scientists to doubt that it carried the genetic code.

 

CIE Specification Reference: - 6 Nucleic acids. 6.1 Structure of DNA. Understanding the structure of nucleic acids allows an understanding of their role in the storage of genetic information. a) describe the structure of nucleotides. b) describe the structure of DNA and explain the importance of base pairing and the different hydrogen bonding between bases (include reference to adenine and guanine as purines and to cytosine, thymine and uracil as pyrimidines. Structural formulae for bases are not required but the recognition that purines have a double ring structure and pyrimidines have a single ring structure should be included).

 

Edexcel (Biology A – Salters-Nuffield) Specification Reference: - Topic 2: Genes and Health. 2.5 i) Know the basic structure of mononucleotides (deoxyribose linked to a phosphate and a base, including thymine, cytosine, adenine or guanine) and the structures of DNA (polynucleotide composed of mononucleotides linked through condensation reactions). ii) Know how complementary base pairing and the hydrogen bonding between two complementary strands are involved in the formation of the DNA double helix.

 

Edexcel (Biology B) Specification Reference: - Topic 1: Biological Molecules. 1.4 DNA and protein synthesis. i) Know the structure of DNA, including the structure of the nucleotides (purines and pyrimidines), base pairing, the two sugar-phosphate backbones, phosphodiester bonds and hydrogen bonds.

 

OCR (Biology A) Specification Reference: - 2.1.3 Nucleotides and nucleic acids. (a) the structure of a nucleotide as the monomer from which nucleic acids are made (the identification of the purines and pyrimidines and the type of pentose sugar and the formation of phosphodiester bonds (the sugar phosphate backbone. (b) the synthesis and breakdown of polynucleotides by the formation and breakage of phosphodiester bonds. (d) (i) the structure of DNA (deoxyribonucleic acid) To include how hydrogen bonding between complementary base pairs (A to T, G to C) on two antiparallel DNA polynucleotides leads to the formation of a DNA molecule, and how the twisting of DNA produces its ‘double-helix’ shape.

 

OCR (Biology B) Specification Reference: - 2.1.4 Nucleic acids. (a) the structure of a nucleotide as the monomer from which nucleic acids are made (the identification of the purines and pyrimidines and the type of pentose sugar and the formation of phosphodiester bonds (the sugar phosphate backbone). (c) (i) the structure of the DNA molecule, including a review of the evidence for complementary bases pairing “Chargaff’s rules”).

 

WJEC Specification Reference: - Core Concepts 5. Nucleic acids and their functions. (a) the structure of nucleotides (pentose sugar, phosphate, organic base). (e) the structure of nucleic acids: DNA bases: purines and pyrimidines; complementary base pair rule; hydrogen bonding and the double helix; antiparallel strands.

AQA Specification Reference: - 3.1.5 The Structure of RNA.

 

CIE Specification Reference: - 6 Nucleic acids. 6.1 Structure of RNA. Understanding the structure of nucleic acids allows an understanding of their role in the storage of genetic information.

 

Edexcel (Biology A – Salters-Nuffield) Specification Reference: - Topic 2: Genes and Health. 2.5 i) Know the basic structure RNA

 

Edexcel (Biology B) Specification Reference: - Topic 1: Biological Molecules. Know the structure of RNA.

 

OCR (Biology A) Specification Reference: - 2.1.3 Nucleotides and nucleic acids. (a) the structure of a nucleotide as the monomer from which nucleic acids are made (the identification of the purines and pyrimidines and the type of pentose sugar and the formation of phosphodiester bonds (the sugar phosphate backbone. Know the Structure of RNA

 

OCR (Biology B) Specification Reference: - 2.1.4 Nucleic acids. (a) the structure of a nucleotide as the monomer from which nucleic acids are made (the identification of the purines and pyrimidines and the type of pentose sugar and the formation of phosphodiester bonds (the sugar phosphate backbone). (c) (i) the structure of the RNA molecule.

 

WJEC Specification Reference: - Core Concepts 5. Nucleic acids and their functions. (a) the structure of nucleotides (pentose sugar, phosphate, organic base). (e) the structure of nucleic acids: RNA.

AQA A Level Biology Specification Reference: - 3.4.1 DNA, genes and chromosomes: In prokaryotic cells, DNA molecules are short, circular and not associated with proteins. In the nucleus of eukaryotic cells, A gene occupies a fixed position, called a locus, on a particular DNA molecule. A sequence of three DNA bases, called a triplet, codes for a specific amino acid. The genetic code is universal, non-overlapping and degenerate. In eukaryotes, much of the nuclear DNA does not code for polypeptides. There are, for example, non-coding multiple repeats of base sequences between genes. Even within a gene only some sequences, called exons, code for amino acid sequences. Within the gene, these exons are separated by one or more non-coding sequences, called introns.

 

CIE A Level Biology Specification Reference: - 6 Nucleic acids and protein synthesis. Explain the term gene. Describe how the information in DNA is used during transcription and translation to construct polypeptides, including the role of messenger RNA (mRNA), transfer RNA (tRNA) and the ribosomes

 

Edexcel A Level Biology (Biology A – Salters-Nuffield) Specification Reference: - Topic 2: Genes and Health: 2.8 Know that a gene is a sequence of bases on a DNA molecule that codes for a sequence of amino acids in a polypeptide chain. 

 

Edexcel A Level Biology (Biology B) Specification Reference: - Know that a gene is a sequence of bases on a DNA molecule coding for a sequence of amino acids in a polypeptide chain. 

 

OCR A Level Biology (Biology A) Specification Reference: - 6.1 Genetics and evolution - 6.1.1 Cellular control: the regulatory mechanisms that control gene expression at the transcriptional level, posttranscriptional level and post-translational level - post-transcriptional level: the editing of primary mRNA and the removal of introns to produce mature mRNA.

 

OCR A Level Biology (Biology B) Specification Reference: - 5.1.3 Gene technologies - post transcriptional editing of mRNA. To include the production of mature mRNA in human cells, the nature of introns and exons and the potential to produce many different mature RNA molecules from a single gene.

 

WJEC A Level Biology Specification Reference: - DNA contains the code for proteins and that between the exons are regions of non-coding DNA called introns.

AQA A Level Biology Specification Reference: - 3.4.2 DNA and protein synthesis -  The structure and function of messenger RNA (mRNA) and of transfer RNA (tRNA).

 

CIE A Level Biology Specification Reference: - 6 Nucleic acids and protein synthesis. Explain  the role of messenger RNA (mRNA), transfer RNA (tRNA) and the ribosomes.

 

Edexcel A Level Biology (Biology A – Salters-Nuffield) Specification Reference: - Topic 2: Genes and Health: 2.6 i) Understand the process of protein synthesis (transcription) including the role of RNA polymerase, translation, messenger RNA, transfer RNA, ribosomes and the role of start and stop codons. ii) Understand the roles of the DNA template (antisense) strand in transcription, codons on messenger RNA and anticodons on transfer RNA.

 

Edexcel A Level Biology (Biology B) Specification Reference: - Know the structure of mRNA including nucleotides, the sugar phosphate backbone and the role of hydrogen bonds. Know the structure of tRNA, including nucleotides, the role of hydrogen bonds and the anticodon.

 

OCR A Level Biology (Biology A) Specification Reference: - 2.1.3 Nucleotides and nucleic acids: transcription and translation of genes resulting in the synthesis of polypeptides. To include, the roles of RNA polymerase, messenger (m)RNA, transfer (t)RNA, ribosomal (r)RNA.

 

OCR A Level Biology (Biology B) Specification Reference: -2.1.4 Nucleic acids - To include, the roles of messenger (m)RNA, transfer (t)RNA, and ribosomal (r)RNA.

 

WJEC A Level Biology Specification Reference: - Core Concepts 5. Nucleic acids and their functions: -(f) the similarities and differences in the structure of RNA and DNA. (l) the transcription of DNA to produce messenger RNA. (m) the translation of mRNA using ribosomes and the structure and function of transfer RNA, to synthesise proteins. (Structure and Function of mRNA and tRNA).

AQA A Level Biology Specification Reference: - 3.1.5 Nucleic acids are important information-carrying molecules. 3.1.5.1 Structure of DNA. 3.4.1 DNA, genes and chromosomes: In prokaryotic cells, DNA molecules are short, circular and not associated with proteins. In the nucleus of eukaryotic cells, DNA molecules are very long, linear and associated with proteins, called histones. Together a DNA molecule and its associated proteins form a chromosome. The mitochondria and chloroplasts of eukaryotic cells also contain DNA which, like the DNA of prokaryotes, is short, circular and not associated with protein. A gene is a base sequence of DNA that codes for: the amino acid sequence of a polypeptide a functional RNA (including ribosomal RNA and tRNAs). A gene occupies a fixed position, called a locus, on a particular DNA molecule. A sequence of three DNA bases, called a triplet, codes for a specific amino acid. The genetic code is universal, non-overlapping and degenerate. In eukaryotes, much of the nuclear DNA does not code for polypeptides. There are, for example, non-coding multiple repeats of base sequences between genes. Even within a gene only some sequences, called exons, code for amino acid sequences. Within the gene, these exons are separated by one or more non-coding sequences, called introns.

 

CIE A Level Biology Specification Reference: - 6 Nucleic acids. 6.1 Structure of DNA. 1.2 Cells as the basic units of living organisms: d) outline key structural features of typical prokaryotic cells as seen in a typical bacterium (including: unicellular, 1–5μm diameter, peptidoglycan cell walls, lack of membrane-bound organelles, naked circular DNA, 70S ribosomes). a) describe the structure of a chromosome, limited to DNA, histone proteins, chromatids, centromere and telomeres. mitochondria (including small circular DNA). Chloroplasts (including small circular DNA).

 

Edexcel A Level Biology (Biology A – Salters-Nuffield) Specification Reference: - Topic 2: Genes and Health: 2.8 Know that a gene is a sequence of bases on a DNA molecule that codes for a sequence of amino acids in a polypeptide chain. Topic 3: Voice of the Genome: 3.4 Know the ultrastructure of prokaryotic cells, including cell wall, capsule, plasmid, flagellum, pili, ribosomes, mesosomes and circular DNA.

 

Edexcel A Level Biology (Biology B) Specification Reference: - Know that a gene is a sequence of bases on a DNA molecule coding for a sequence of amino acids in a polypeptide chain. v Know the ultrastructure of eukaryotic cells and the functions of organelles, including: nucleus, nucleolus, mitochondria.

 

OCR A Level Biology (Biology A) Specification Reference: - The Structure of DNA. The structure of a chloroplast: The components of a chloroplast including outer membrane, lamellae, grana, thylakoid, stroma and DNA. The structure of the mitochondrion - The components of a mitochondrion including inner and outer mitochondrial membranes, cristae, matrix and mitochondrial DNA.

 

OCR A Level Biology (Biology B) Specification Reference: - 2.1.1 Cells and microscopy (i) the ultrastructure of a typical eukaryotic plant cell such as a palisade mesophyll cell and a prokaryotic cell, as revealed by an electron microscope. To include the structure and function of the mitochondria, nucleus and nucleolus. The ultrastructure a prokaryotic cell, as revealed by an electron microscope. The structure and function of chloroplasts, circular DNA.

 

WJEC A Level Biology Specification Reference: - DNA contains the code for proteins and that between the exons are regions of non-coding DNA called introns. The structure and function of the mitochondria; chloroplasts. 

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