Chapter 10 DNA,RNA

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Learning Intentions

Nucleic acids

What are nucleic acids?

• Nucleic acids are large biomolecules made from sub-units called nucleotides.

Examples:

• DNA

• RNA

The structure of DNA

• DNA is an abbreviation for deoxyribonucleic acid.

• James Watson and Francis Crick discovered the structure of DNA in 1953. They were awarded a Nobel prize in 1962. There findings were based on the research of Rosalind Franklin.

• The structure of DNA can be considered under these three headings:

  • Nucleotides

  • Base pairs

  • Double helix

Nucleotides

What is the sub-unit of DNA?

• A nucleotide

What is a nucleotide?

• A nucleotide consists of three parts: a phosphate group, a sugar and a nitrogen-containing base.

Nucleotides

The phosphate group is normally represented by the symbol ‘P’.

The sugar in DNA is deoxyribose (a five-carbon sugar), represented by the symbol ‘D’.

There are four bases in DNA:

• Adenine (A)

• Thymine (T)

• Guanine (G)

• Cytosine (C)

Nucleotides

• A chain of nucleotides is called a polynucleotide.

Base pairs

What is meant by a complementary base pair?

• Bases that match each other.

Examples:

• Adenine and thymine each form two weak hydrogen bonds.

• Guanine and cytosine each form three weak hydrogen bonds.

At The Giants Causeway

Base pairs

• If one strand has the base sequence ATTGCCCTTGA, then the complementary strand must have the sequence ??

ATTGCCCTTGA

TAACGGGAACT

Double helix

• The outer strands of the double helix (the ladder shape) are composed of phosphate and deoxyribose groups.

• The rungs of the double helix are the base pairs.

The relationship between chromosomes,
DNA and genes

• Chromosomes are composed of 60% protein and 40% DNA.

• DNA is tightly wrapped around the protein.

• Genes are sections of DNA found along a chromosome.

• These sections of DNA on a gene represent a code used by the cell for the formation of a protein.

Chromosome

HEK293 cell’s

Structure of RNA

• RNA is an abbreviation for ribonucleic acid.

What is the sub-unit of RNA?

• A nucleotide.

• An RNA nucleotide has a phosphate, a sugar (ribose) and a base (A, U, G and C).

• In RNA, adenine complements uracil and guanine complements cytosine.

Structural differences between RNA and DNA

DNA

• Contains the sugar deoxyribose

• Has the bases AT and GC (has thymine)

• Is double-stranded (double helix)

• Longer

RNA

Contains the sugar ribose

Has the bases AU and GC (has uracil)

Is single-stranded

Shorter

The function of DNA

What are the three functions of DNA?

• Stores inherited information.

• Passes inherited information from cell to cell and from generation to generation.

• Causes proteins to be formed.

The function of DNA

Stores inherited information

• The inherited information in each gene causes the production of a protein.

• It is the proteins that control all the activities of the cell.

Passing on inherited information

• DNA can make an exact copy of itself.

• When the cell later divides into two, each new cell will carry two identical copies of the DNA.

• This means that the inherited genes are passed on from cell to cell within the organism.

• Parents pass their chromosomes on to their offspring via sperm and egg cells.

Cell dividing to form two cells with identical DNA

The function of DNA

DNA makes protein

• Genes, or DNA, work by controlling the production of proteins.

• Gene expression is the way in which a gene causes the production of a protein.

• Each gene causes the production of a type of RNA.

• The RNA molecule moves from the DNA in the nucleus to a ribosome located in the cytoplasm.

• The RNA causes a ribosome to assemble a number of amino acids in a particular sequence into a chain.

• The chain of amino acids moves out from the ribosome and folds to produce a functional protein.

DNA ➜ RNA ➜ protein

The function of DNA

Coding and non-coding DNA

• Only a small amount of our DNA carries the code for the production of proteins.

• Up to 98% of our DNA does not cause the production of proteins.

• Coding DNA has the genetic instructions to produce a protein.

• Non-coding DNA has genetic instructions that do not produce a protein.

The function of RNA

• DNA carries the code to allow for the production of proteins. However, DNA is found in the nucleus, while proteins are made in the ribosome.

How does DNA get the code to the ribosome?

• The function of one type of RNA is to carry genetic instructions from the nucleus to the cytoplasm (or from DNA to the ribosome).

• Another type of RNA brings the correct amino acids to the ribosome so that the correct protein is formed.

Relationship between genes,
proteins and traits

What is a characteristic?

• A characteristic is an inherited feature that varies among individuals.

Example: eye colour

What is a trait?

• A trait is one variant (or version) of a characteristic.

Example: blue eyes or brown eyes, freckles

Relationship between genes,
proteins and traits

• Genes make proteins. Proteins (often enzymes) are responsible for forming traits.

• For example, the gene(s) for brown eyes causes the production of one or more proteins.

• These proteins then cause the production of brown pigments in the eyes, which result in the trait of brown eyes.

The genetic code (HL)

What is the genetic code?

• The genetic code is the set of rules by which the sequence of the bases (or nucleotides) in DNA acting in groups of three determines the sequence of the amino acids in a protein.

• The genetic code is based on codons or triplets.

• A codon (or triplet) is a sequence of three nucleotides (or bases) in DNA or RNA that specifies a particular amino acid.

The genetic code

The three types of codons

Codons may cause three possible outcomes:

• A start codon indicates the beginning of a gene (but it is not involved in the production of the protein).

• Most codons code for particular amino acids.

• A stop codon indicates the end of a gene (but is not involved in the production of the protein).

Codons

Anti - Codons

• An anticodon is a sequence of three bases in one type of RNA that is complimentary to a sequence of three bases (a codon) in another type of RNA

Learning Intentions

Question 1

Question 2

Question 3

Question 4

Answer 1

Answer 2

Answer 3

Answer 4

Exam Questions

• 2004 Section C Question 13 Part A

• 2007 Section C Question 10 Part C

• 2007 Section C Question 10 Part A

• 2008 Section C Question 14 Part B

• 2011 Sectio B Question 9 Part A

• 2012 Section C Question 10 Part A

• 2014 Section C Question 10 Part A

• 2015 Section B Question 7 Part A

• 2018 Section C Question 13 Part A

• 2019 Section C Question 11 Part A

• 2020 Section A Question 4

• 2022 Section C Question 13 Part A

• 2023 Section A Question 4