6.1.1 Cellular control

At which levels is Gene-expression controlled at

Transcriptional

Post- transcriptional

Translational

Post- Translational

what are Transcription factors?

Proteins that bind to DNA and switch genes on or off

Function of non coding DNA

regulate gene expression → switching on or off

what are the types of Transcriptional factors

Activators → activate transcription

repressors → repress transcription

in eukaryotes how do Transcription factors work

TF are complimentary to the DNA and bind to specific DNA sites on target genes

how can molecules control the synthesis of some proteins ?

shape of transcription factors can be altered by the binding of some molecules ( sugars)

no longer complimentary

In prokaryotes what do transcription factors bind to?

Operons

what is a operon

Section of DNA that contains structural and regulatory genes and control elements

function of structural genes

codes for proteins not involved in DNA regulation (enzymes )

what does the control element contain

the Promoter → DNA sequence that RNA Polymerase binds to ( think polymerase → Promoter PP)

the operator → DNA sequence that transcription factors bind to

Function of regulatory genes?

Codes for an activator or a repressor

Prokaryotic operon ( Image)

what is the operon in E coli called

Lac operon

which enzymes are used to help E coli digest lactose

β- galactosidase

lactose permease

what are the structural genes on the Lac operon called?

LacZ, LacY and lacA

what happens on the Lac operon when glucose is present

regulatory gene produces a lac repressor protein

binds to operator site and blocks transcription → RNA polymerase cant bind to promoter

what happens on the Lac operon when lactose is present

lactose binds to repressor altering shape → no longer complimentary

cant bind to operator site

RNA polymerase beings transcription of structural genes

what is the difference between Exons and Introns

Exons → sections of DNA that code for amino acids

Introns → Section of DNA that do not code for amino acids

what type of organisms have exons and Introns

Eukaryotic

DO prokaryotes contain Introns and why

No

mRNA is produced directly from DNA without splicing

what is a mutation?

Change in DNA base sequence

What are the types of DNA mutations

Gene mutation

Chromosome mutation

what is a gene mutation

Change in a gene DNA sequence

what is a chromosome mutation

Change in large sections of chromosomes or change in number

what are the type of mutations

Indel mutation → insertion or deletion of a base

Substitution → a base gets replaced by another base

what do Indel mutations cause

Frameshift mutation

what is a Frameshift mutation

Changes how the codon is read → codes for a different amino acid

what is a point mutation

mutation that only affects bases

what can increase the rate at which mutations occur

exposure to mutagenic agents ( UV light, ionising radiation)

which mutation has a larger affect indel or substitution

Indel → result frameshift mutations

affect more amino acids than sub

larger overall effect on protein structure

what are the types of effects a mutation can have

silent

Beneficial

Harmful

when are frameshift mutations not caused by Indel mutations

number of bases added / removed are a multiple of 3

no frameshift mutation → following codon is still the same

How can a mutation have a silent effect on protein function?

Base sequence is degenerate → mutated codon still codes for the same amino acid

Substitution of amino acid with similar properties to the original amino acid might leave 3° or 2° structure unchanged

mutation might change part of the tertiary structure away from the functional part of the protein → away from active site

Mutation is in non-coding section of DNA

How can mutations have a beneficial effect ?

enhance the functioning of a protein

passed through natural selection

How can mutations be harmful?

create a malfunctioning protein

prevents amino acid from being coded → no protein

what are some diseases caused by a harmful mutation

Cancer

sickle cell anaemia

What are the types of point mutation ?

Nonsense → codon mutated into a stop codon

Missense → codes for different amino acid in the polypeptide

Structure of chromatin

Section of DNA tightly coiled around a histone protein

What is Heterochromatin?

Tightly coiled DNA in cell division

when is Heterochromatin formed

Chromosomes becomes coiled and condense in prophase → forms Heterochromatin

Advantages of Heterochromatin being formed

prevents DNA from being damaged during cell division → tightly coiled.

What happens in Transcriptional gene control of eukaryotes

Histone is modified for chromatin remodelling

difference between heterochromatin and Euchromatin

Heterochromatin → DNA is tightly wound to histone, there’s no transcription

Euchromatin → DNA is loosely wound to histone, transcription occurs as

Why does transcription occur in Euchromatin

RNA polymerase can binds to the gene as DNA is loosely wound to histone → Transcription occurs

Why does transcription not occur in Heterochromatin

Gene is inaccessible

RNA polymerase cant bind to gene as DNA is tightly wound to the histone → no transcription.

what is Euchromatin and when is it formed?

loosely wound DNA to histone in interphase

How does Heterochromatin form Euchromatin ?

Acetylation or phosphorylation

Negatively charged ions that decrease the positive charge of the histone protein → negatively charged DNA binds more loosely → Weaker ionic bond → allows transcription to occur

How to convert Euchromatin to Heterochromatin

Methylation

Increase the hydrophobic nature of histones → more tightly wound DNA to histone

What level of gene control is the Lac operon

Transcriptional level of control in prokaryotes

What happens when there’s a lack of glucose as respiratory substrate in prokaryotes

Activate the Lac operon to break down lactose instead

What happens when there is glucose available on method

the regulatory gene ( LacI) codes for a repressor protein

repressor protein binds to the operator, blocking the promoter

RNA polymerase cant bind to promoter → No transcription

What happens when there is lactose available on Lac operon

Lactose binds to the repressor protein → changes the shape so no longer complimentary to the operator

Repressor protein unbinds from operator → allows RNA polymerase to bind to the promoter → transcribe the structural genes

Effect of cAMP on Lac operon

cAMP binds to and activates RNA polymerase

increases the activity of RNA polymerase → increases rate of transcription

What is the effect of glucose on cAMP in the Lac operon

high Glucose conc inhibits adenyl cyclase

Glucose decreases cAMP concentration in cell

less cAMP binding to RNA polymerase

decreases the rate of transcription

Effect of a nonsense mutation on Protein

Produce a Truncated (shortened ) protein

What are the two Transcriptional levels

Chromatin remodelling

Lac operon

what process happens in Post - Transcriptional level eukaryotes

RNA splicing

What happens during RNA splicing

introns and exons are copied into mRNA → forms Pre- mRNA

Introns are removed from pre-mRNA → exons join together forming mature mRNA

why don’t prokaryotes under splicing ?

No introns in prokaryotic DNA

How to stabilise mRNA and prevent degradation during splicing

Add an adenine tail

Add a cap ( modified nucleotides)

splicing image

What are the ways to switch translation off at a translational level

Degrade the mRNA

add a inhibitory protein to bind to mRNA → mRNA cant bind to ribosome

What are the ways to switch translation on at a translational level

Activate the protein with cAMP → allows mRNA to bind to ribosome

alters 3D structure of protein

what type of reaction activates initiation factors at translational level

Phosphorylation by protein kinases

which molecule activates protein kinases

cAMP

what are the post- translational control of gene expression?

Add non-protein groups ( Golgi apparatus processing)

Activate and modify with cAMP

modify the amino acids

How many base pairs are in the Homeobox

180 base pairs

How many amino acids make the homeodomain

60 amino acids

what are Homeobox genes ?

Regulatory genes that control body development

what type of organism contain homeoboxes

Eukaryotic

In what kingdoms are homeobox genes found in

Fungi

Animalia

plants

Protoctista

what processes do Homeobox genes regulate

Mitosis

apoptosis

What is apoptosis

programmed cell death

which stimuli does apoptosis and mitosis respond to

Internal

External

why is the Homeobox highly conserved in eukaryotes ?

Organisms have a basic structure

where are Hox genes found

Animals only

what are Hox genes?

Homeobox genes found in animals

Suggest reason for animal with deformity

Hox genes are mutated → results in mutated body arrangement

Hox genes are regulatory genes that control body development

Hox genes are highly conserved

Apoptosis process ( Image)

Examples of apoptosis

Destroys cells between fingers and toes → prevents webbed fingers

Destroys WBC → prevents auto immune diseases

function of enzymes and phagocytes in Apoptosis

Enzymes → digest cells content

phagocytes → removes the products prevent damages to surrounding tissue

suggest role of homebox genes in brain development

Switch genes on and off in brain → form specialised nerve cells

Determine the anterior and posterior regions

Outline general role of homeobox genes

Code for body development in organisms

Regulated by mitosis and apoptosis

involved in gene regulation → switch genes on and off → determines cell identity