6.1.1 cellular control

Mutation

A random change to the DNA molecule. This generally involves a change in the base sequence of the DNA

Where do mutations occur

DNA

What if the effect if mutations occur during mitosis

called somatic cell mutations. They will just affect the cell in which the mutation occurs, unless they are cancerous in which they can be spread. These can not be passed onto offspring

What is the effect if mutations occur during meiosis

The organism produced from the gamete will have the mutation in every cell of their body. These are passed onto offspring

What is the effect on a protein if a mutation occurs in a gene

Primary structure of the protein it codes for could be altered. This may change the final 3D shape of the protein so it doesn't work properly

Classes of mutations

Point mutations (one base pair replaced another). Also a substitution mutation

Frameshift mutations (insertions or deletions of nucleotides in the length of DNA)- also called indel mutations

Types of point mutations

silent, missense, nonsense

Point mutation 1: silent

the mutation does not alter the amino acid sequence of the polypeptide. this is because certain codons may code for the same amino acid as the genetic code is degenerate

Point mutation 2: missense

the mutation alters a single amino acid in the polypeptide chain

Point mutation 3: nonsense

The mutation creates a premature stop codon, causing the polypeptide chain produced to be incomplete and therefore affecting the final protein structure and function

Insertion mutations

when a nucleotide with a new base is randomly inserted into the DNA. It changes the amino acid that would've been coded by the original base triplet as it creates a new different triplet of bases.

effect of insertion mutations on the function of proteins

Changes the triplets further on in the DNA sequence. This is sometimes known as a frameshift mutation. This may dramatically change the amino acid sequence produced from this gene and therefore the ability of the polypeptide to function

Deletion mutation

When a nucleotide is randomly deleted from the DNA sequence. It changes the amino acid that would've been coded for. It has a knock on effect by changing the groups of three bases further on in the DNA sequence. This may dramatically change the amino acid sequence produced from this gene and therefore the ability of the polypeptide to function.

Effects on mutations: production of new protein

results: gain of reproductive advantage

eg: large brain to body ratio, sickle cell

Effects on mutations: neutral mutation

result: no change

Eg: ability to roll tongue

Effects on mutations: production of inferior or no protein

result: fatal/disease causing

Gene expression

The process of switching on genes so that proteins are made

Inducible enzymes

some enzymes are only synthesised when needed

Inducer molecule

The molecule that causes the gene to be switched on

E coli

Can adapt to its environment by producing enzymes to metabolise certain nutrients but only when those particular nutrients are present. E coli can synthesise over 3000 different enzymes

How does E coli respire

normally respires using glucose but can also respire using lactose. To do this it needs to synthesise 2 enzymes:

B galactosidase- which hydrolyses lactose into glucose and galactose

lactose permease- which makes the E. coli plasma membrane more permeable to lactose (it does this by inserting lactose specific transporter proteins into the E coli membrane

operon

length of DNA made from structural genes and control sites

structural genes

code for protein

control sites

operator and promoter region of the DNA

What are the 3 structural genes of the lac operon

lacZ, lacY, lacA which produce proteins that help the bacteria digest lactose

Lac operon in E. coli-lactose is not present

Regulatory gene produces the lac repressor which is a transcription factor that binds to the operator site when there's no lactose present. This blocks transcription because RNA polymerase can't bind to the promoter. Therefore LacZ/LacY are not transcribed

Lac operon in E.coli-lactose is present

When lactose is present, it binds to the repressor, changing the repressor's shape so that it can no longer bind to the operator site. RNA polymerase can now begin transcription of the structural gene. Therefore the structural genes can be transcribed

Gene expression in eukaryotes

Transcription factors bind to specific DNA sites near the start of their target genes- genes they control the expression of

Gene expression at a post transcriptional level

1)Genes in eukaryotic DNA contains sections that don't code for amino acids

2)These sections of DNA are called introns. All the bits that do code for amino acids are called exons

3)During transcription the introns and exons are both copied into mRNA. mRNA strands containing introns and exons are called primary mRNA transcripts

4)Introns are removed from from primary mRNA strands by a process called splicing-introns are removed and exons joined forming mature mRNA

5)mature mRNA then leaves the nucleus for translation

How does cAMP activate proteins at the post translational level

Protein activation is controlled by molecules eg hormones

Some of these molecules work by binding to cell membranes and triggering the production of cyclic AMP inside the cell

cAMP then activates proteins inside the cell by altering their 3D structure

How does cAMP activate PKA

1)PKA is an enzyme made of 4 subunits

2) When cAMP isn't bound the four units are bound together and are inactive

3)When cAMP binds ,it causes a change in the enzyme's 3D structure, releasing the active subunits-PKA is now active

Body plan

Where organs/body parts are found within an organism is known as the body plan

Homeotic genes

A family of genes involved in anatomical development of an organism

Several of these genes contain homeobox sequences found in plants, animals and fungi

Homeobox sequence

180 bp

this would code for a 60 amino acid sequence called the homeodomain sequence

Homeobox genes are highly conserved

The same homeobox genes are found in all plants, animals and fungi.

They are highly conserved because:

They are fundamental to the correct organisation of the body plan

Without it some body parts will not develop correctly so the individuals is unlikely to survive

Hox genes

Subset of homeobox genes, found only in animals; involved in formation of anatomical features in correct locations of body plan.

Regulate the development of embryos along the anterior-posterior axis

Proteins they code for act as transcription factors. This means they can switch on and off genes.

Mutations can lead to drastic changes in the body plan

How do hox genes control development

Homeobox sequences code for a part of the protein called the homeodomain.

The homeodomain binds to specific sites on DNA, enabling the protein to work as a transcription factor.

The proteins bind to DNA at the start of developmental genes, activating or repressing transcription and so altering the production of proteins involved in the development of the body plan.

This can lead to apoptosis or mitosis

Suggest what might happen at the cellular control level if there is a mutation in one of the hox genes

1)The mRNA produced may code for a different primary sequence.

2)This will change the shape of the transcription factor

3)The transcription factor won't be able to bind to the DNA so It will alter gene expression

4)This may increase/decrease mitosis or apoptosis