cellular control

Gene mutations:

what are addition mutations?

this is where one or more base are added to the DNA sequence

Gene mutations:

what are deletion mutations?

this is where one or more bases are removed

Gene mutations:

what are substitution mutations?

this is where one or more bases are changed in the sequence

Gene mutations:

what is a point mutation?

its an alteration in a single nucleotide base pair for example addition, substitution or deletion of a nucleotide

Gene mutations:

what is a frameshift?

its a genetic error from adding or deleting DNA bases in numbers not divisible by three

Gene mutations:?

what are the effects a frameshift?

changes the proteins tertiary structure can cause harmful mutations

Gene mutations:

what is a beneficial mutation?

its a genetic change that improves an organism’s fitness, increasing its chance of survival in the environment

Gene mutations:

how does the protein structure change in a beneficial mutation?

proteins and polypeptides usually involve subtle, specific single amino acid swaps this can change the proteins tertiary shape to suit the new environment

Gene mutations:

what is a harmful mutation?

its a genetic that negatively affects an organism’s health and survival success

Gene mutations:

how does the protein structure change in a harmful mutation?

it alters its amino acid sequence which disrupts the DNA base changes which disrupts the normal 3D folding of secondary, tertiary and quaternary structures by changes amino acid interactions and creates unstable structures

Gene mutations:

what is a neutral mutations?

DNA change doesn’t affect an organism’s survival or reproduction but accumulates a genetic drift

Gene mutations:

how does the protein structure change in a neutral mutation?

the DNA base sequence changes but the resulting amino acid sequence and 3D structure stays the same

Chromatin remodelling:

what is chromatin remodelling?

it’s the process of altering DNA’s packaging around histones to control gene expressions, making DNA accessible for transcription or blocking it

Chromatin remodelling:

what is heterochromatin?

its a tightly wound DNA causing chromosomes to be visible during cell division whereas euchromatin is loosely wound DNA present during interphase (transcription)

Chromatin remodelling:

key characteristics of heterochromatin

structure: highly compact, dense and typically located at the nuclear periphery or around the nucleus

gene activity: generally gene-poor and transcriptionally silent (inactive) because transcription factors cannot easily access it

composition: often rich in repetitive DNA sequences and specific histone modifications (e.g. H3K9 methylation) that promote its compact state

Chromatin remodelling:

what is euchromatin?

its loosely(less condensed) packed forms of chromatin (DNA and proteins) that is rich in active genes

Chromatin remodelling:

key characteristics of euchromatin

structure: loosely packed, open and less condensed

activity: transcriptionally active (genes are actively being read to make RNA and proteins)

compositions: contains most of the cell’s active genes including housekeeping genes

location: found in the interphase nucleus, where cells are actively working

molecular marks: characterised by histone acetylation (loosens DNA) and low DNA methylation which promotes expression

Chromatin remodelling:

what is a histone modification?

DNA coils around histones are positively charged and DNA is negatively charged, so histones can be modified to increase or decrease the degree of packaging

Chromatin remodelling:

key histone modifications and their effects

Acetylations: adds acetyl groups (often lysine), neutralises positive charge, loosens DNA-histone binding leading to open chromatin and gene activation

Methylation: adds methyl groups (to lysine/ arginine), which can active or repress genes depending on the location (e.g. H3K4me3 activates and H3K27me3 represses)

Phosphorylation: adds phosphate groups to serine/tyrosine and threonine, which introduces negative charge, influencing DNA binding and chromatin structure

Lac operons:

what is an operon?

it is a group of genes controlled by the same regulatory mechanisms and expressed at the same time

Lac operons:

what is a structural gene?

they are proteins that are not involved in DNA regulation

Lac operons:

what is a regulatory gene?

they are proteins that are involved in DNA regulation

Lac operons:

structure of a lac operon

. lacI is the regulatory gene (codes for repressor protein)

. structural gene lacZ which codes for lactase

. structural gene lacY codes for permease which allows lactose into the cell

. structural gene lacA codes for transacetylase

. operator

. promoter for structural gene

. its located on the left upstream of the lac operon on the bacterium’s DNA

. promoter for the regulatory gene

Lac operons:

the lac operon characteristics

. the expression of beta-glactosidase is responsible for hydrolysis of lactose in the E.coli

. the lactase enzyme breaks down lactose so that it can be used as energy in the bacterium’s cell

. its a inducible enzyme so its only synthesised when lactose is present which prevents the bacteria from wasting energy and materials

Lac operons:

when lactose is absent

1) the regulatory gene is transcribed and translated to produce lac repressor proteins

2) the lac repressor protein binds to the operator region upstream of lacZ

3) due to the repressor protein being present RNA polymerase is unable to bind to the promoter region

4) transcription of structural genes do not take place and no lactase enzyme is synthesised

Lac operons:

when lactose is present

1) there is an uptake of lactose by the bacterium

2) the lactose binds to the second binding site on the repressor protein

3) this distorts its shape so cant bind to the operator site

4) RNA polymerase is now able to bind to the promoter region and transcription can take place

5) the mRNA from all 3 structural genes are translated

6) enzyme lactase is produced and breaks down lactose and the energy is now used by the bacterium

Lac operons (in eukaryotes):

how transcription factors in eukaryotes work

. some transcription factors bind to the promoter region on a gene

. this binding can either allow or prevent the transcription of genes

. presence of transcription factors either increase or decrease the rate of transcription

Lac operons (in eukaryotes):

gene control in oestrogen

1) oestrogen diffuses through the plasma membrane and into the nucleus

2) oestrogen then attaches to the receptor that is contained with protein complexes

3) this then causes oestrogen to change the shape of the receptor

4) as a result, the receptor moves away from its normal protein complexes and binds to a promoter region of one of its target gene

5) this allows RNA polymerase to bind and begin transcribing that gene

Lac operons (in eukaryotes):

what is gibberellin?

. gibberellin is a hormone in plants that controls seed germination

. when gibberellin is applied to a germinating seed there is an increased amount of mRNA for amylase present

Lac operons(in eukaryotes):

what is the mechanism of gibberellin

. breakdown of DELLA protein by gibberellin for amylase synthesis

. repressor protein DELLA

. transcription factors (PIF)

. promoter of amylase gene

. amylase gene

. gibberellin

. gibberellin receptor and enzymes

Lac operons (in eukaryotes):

gene control of gibberellin

1) DELLA repressor protein is bound to transcription factor, preventing it from binding to the promoter of the amylase gene so there is no transcription

2) gibberellin binds to gibberellin receptor and the enzyme starts to break down of DELLA

3) transcription factors no longer is bound to DELLA protein so binds to the promoter of the amylase gene

4) transcription of amylase begins and amylase is produced

Body plans and hox genes:

what is the polarity of an organism?

its where the head/tail and front/back of an organism develops

Body plans and hox genes:

what is the segmentation of organisms?

they are organisms such as insects and mammals that are the distinct body parts e.g. abdomen and thorax

Body plans and hox genes:

what are body plans determined by?

they are determined at the embryo stage of development, and is controlled by a family of genes known as homeobox genes

Body plans and hox genes:

what are homeobox genes?

homeobox genes are a family of master regulatory genes containing a conserved DNA sequence (the homeobox) that codes for a protein region (homeodomain)

Body plans and hox genes:

what do homeobox genes code for?

transcription factors

Body plans and hox genes:

what do transcription factors ensure in body plan development?

. they control which genes are being expressed at a particular time and in particular cells

.