Transcript Problems in Replication and Protein Synthesis

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 Outcomes
Missense – 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)