Gene Mutations and Expression

Mutations-mutation- random change in genetic material

-can happen during replication, transcription, translation, or cell division

Point Mutations-Point mutation – a single base pair is affected

-It could be a deletion, insertion, or substitution.

Substitution

Insertion• Extra base pair is added (causes a frameshift)

Deletion• Base pair is removed (causes frameshift)

Duplications-duplication- part of the DNA is duplicated

Inversions-inversion - part of the DNA is reversed

A-T-C-G-T-T-G-C

A-T-C-G-T-C-G-T

Translocations

-part of the DNA is moved to a different spot

A-A-A-T-C-G-T-A-C

T-C-G-A-A-A-T-A-C

Mutation OutcomesMissense – the wrong amino acid is added

Mutation Outcomes• Nonsense – a stop codon is produced early causing

the amino acid chain to end early.

Mutation Outcomes • Silent – although the wrong codon is produced but the

correct amino acid is sill added (thus no change)• Wobble – more than one codon can code for the same

amino acid. (makes silent mutations possible)

Prokaryotic Gene Regulation• Operator – a control site within the promoter that can be

blocked to stop transcription (turns the gene off)• Repressor – a protein that slides into the operator to block

transcription (the RNA polymerase cannot attach and pass)• Operon – promoter + operator + genes they control

Co-repressor• Co-repressor – a molecule that combines with the repressor

to change the repressor into its active form. (thus turning the gene off)

• Ex. E. Coli in our colon only make the amino acid Tryptophan if we are not providing it for them.

Negative regulation• Negative regulation – gene is off until turned on• Repressor is naturally active • Ex. If no lactose (from milk) is present in the colon E. Coli

does not produce enzymes to break down milk

Inducer (negative)• Inducer – molecule that bonds with the repressor to make it

inactive (turns the gene on)• If milk is present E. Coli turns on genes to produce

enzymes to break down the milk.

Positive Gene Control• Positive regulation – even though the repressor is inactive

and the gene is on, protein production must be stimulated.• Ex. If lactose and glucose are both present E. Coli chooses

to use glucose and does not produce enzyme to break down lactose (even though the lactose operon is on)

Activator

Activator (positive)• Activator – stimulates the production of a protein in a gene

that is on (calls for RNA polymerase to attach)• If glucose is in short supply and lactose is available, E. Coli.

will produce enzymes to breakdown lactose.

Activator

Eukaryotic Regulation• Enhancers – sites that call for specific activators to

stimulate the production of certain proteins.

Histone Acetylation• Histone Acetylation – acetyl groups are added to histone

tails (neutralizes their charges)• Histones spread exposing DNA so transcription can be

initiated.

DNA Methylation• DNA methylation – a

methy group is added to

a base.

(usually found in

inactive genes)

Proteasomes • Proteasomes - degrade old protein• Ubiquitin – molecules added to proteins needed to be

broken down.

Micro and Small Interfering RNA• Micro RNA (miRNA) – single stranded degrades or blocks

translation of mRNA.• Small Interfering RNA (siRNA) - double stranded but

functions similarly to siRNA (may help fight viruses)