Cellular Control Flashcards
What phase of the cell cycle are mutations most likely to occur?
S phase
What can increase the rate of mutation?
Mutagenic agents which can be chemical, biological or physical like x-rays
What is a base substitution mutation?
A single nucleotide base is replaced by another.
What is a base insertion mutation?
The insertion of a single nucleotide base.
What is a base deletion mutation?
The removal of a single nucleotide base.
What is a frame shift mutation?
When after the point of mutation every base shifts which codon it’s read in.
What are types of substation mutation?
• A non-sense mutation
• A missense mutation
• A silent mutation
What is a non sense mutation?
When the codon is now a STOP codon so translation stops at the point of mutation.
What is a missense mutation?
When there is a change to a single amino acid at the point of the mutation. Could or could not change the protein
What is a silent mutation?
Is when there is no change to the primary structure of the polypeptide despite the change in the nucleotide base
The genetic code is degenerate which causes the silent mutation
What types of effects can mutations cause?
• Neutral (have no effect)
• Harmful effects
• Beneficial
What are some examples of harmful mutations?
• cancer
•genetic diseases
• FULL stickle cell - shortness of breath, fatigue, crescent moon shaped RBC’s
• nonsense mutation in DMD gene - don’t produce dystrophin protein
• HCM
What are some examples of beneficial mutations?
• often lead to evolution
• sickle cell TRAIT - resistant to malaria
• HIV resistance
Define gene expression
Conversion of the information encoded in a gene into a functional gene product (usually just a protein but sometimes just RNA)
Define gene regulation
The control of the gene expression
- switching certain protein productions on and off
Define regulatory genes
The products of these genes control the expression of structural genes
Define structural genes
They code for any RNA or protein product other than a regulatory factor
Define transcription factors
Made by regulatory genes bind to DNA near structural genes to switch genes on (activator) or off (repressor)
What is Lac operon simple?
•found in E-coli (bacteria)
• humans don’t have one
• E-coli need glucose
Describe the regulatory factors on transcriptional level?
• chromatin remodelling - if it’s loosely associated it’s called euchromatin, if it’s tightly wound it’s called heterochromatin
• transcription can only occur in euchromatin as there is space for RNA polymerase to attach to the promotor region to create mRNA strand.
• faster rate of transcription= more protein made and view versa
Describe the regulatory factors on post-transcriptional level?
• determines whether introns are removed or not
• splicing - non coding sections called introns (on pre-mRNA) are removed by being cut out with enzymes
• makes a structural product
Describe the regulatory factors on translational level?
Proteins are modified in the Golgi - can be modified so they don’t work anymore.
Describe the regulatory factors on translational level?
Slow down protein synthesis
To metabolise lactose what proteins must be present?
B-galactoside and lactose permase
When are the genes B-galactoside and lactose permase transcribed and expressed?
When lactose is present
If lactose is not present why are the genes to make enzymes for lactose not transcribed and translated?
There is no need for a cell to waste energy when there is not lactose to break down
The promoter region is followed by a nucleotide sequence known as the what?
Operator
After the operator nucleotide sequence, the sequences for which genes are found?
Lac Z and Lac Y
Where is the Lac I protein gene found?
At a site away from the lac operon
What is the Lac I protein?
Inhibitor/Repressor
What does the Lac I protein bind to?
The operator when lactose is not present
What happens when the Lac I protein is bound to the operator?
RNA polymerase can bind to the promoter, but cannot get past and transcribe the genes due to the Lac I protein.
When lactose is present where does Lac I bind to?
The Lac I protein binds to lactose, resulting in a conformational change.
What happens once the Lac I protein has bound to lactose, resulting in a conformational change?
The Lac I-lactose complex drops off from the operator, so RNA polymerase can now proceed and transcribe the genes required for lactose metabolism. Lactose can now be broken down for energy.
What happens as the levels of lactose decrease?
The concentration of Lac I-lactose complex decreases, and the now free Lac I protein can again bind onto the operator, preventing transcription of the lactose metabolising genes - so the lac enzymes are not produced.
What is the function of cAMP in regulation of the lac operon?
It speeds up the rate of transcription
What is the term which refers to a contiguous set of bacteria genes which are under coordinate control?
Operon
What is the effect on transcription, of the structural genes of the lac operon is observed, when lactose is present in the environment?
It causes transcription to occur/ switch on
Describe how the genes lac Z and lac Y are switched on in bacteria that are moved into nutrient medium that contains lactose
Lactose binds to the repressor causing a conformational change. It is the operator site so RNA polymerase can move from the promoter to transcribe Lac Z Lac Y and Lac A
What are the coding regions of DNA called?
Exons
What are the non-coding regions of DNA called?
introns
What is the process called where the strand of pre/primary mRNA has its introns removed?
Splicing
Transcriptional level - The Lac operon - what happens when there’s no lactose present?
- Regulator gene makes repressor protein
- As there is no lactose present the repressor is the correct shape to join to the operator region and the promotor.
- This blocks the binding site (promotor) so RNA polymerase can’t attach = no transcription
Transcriptional level - The Lac operon - what happens when lactose is present?
- Regulatory gene produces repressor protein.
- A molecule of lactose attaches to a receptor site on the repressor protein.
- This changes the shape of the repressor.
- Repressor can no longer attach to operator and promotor.
- RNA polymerase can now attach at promoter
- Makes 3 molecules - galactosidase which breaks down lactose, permease proteins which makes cell more permeable to lactose and an additional molecule to allow enzyme to work.
What is the function of homeobox genes?
They are regulatory genes. By regulating which genes are expressed in different parts of an organism, homeobox genes control the development of the organism body and ensure structures develop in the correct positions.
What is the structure of a homeobox gene?
Homeobox sections of DNA are 180 base pairs long
What do homeobox genes encode?
They code for polypeptide sequences that are 60 amino acids long. These polypeptides are called homeodomains which are transcription factors that bind to DNA and switch genes on and off.
What are some examples of the developmental roles played by homeobox genes?
They determine the tail and head of an organism (i.e. its polarity) an regulate the balance between mitosis and apoptosis.
How do homeobox genes differ between species?
The base sequences of homeobox gees are similar in plants, animals and fungi, but different species have different numbers of homeobox genes. For example, invertebrates possess approximately 100 and vertebrates have approximately 200 of these genes. Hox gene are a subset of homeobox genes that are only present n animals.
What are homeobox genes found in?
Clusters
Why do homeobox genes not mutate easily?
Highly conserved - haven’t evolved much
What is apoptosis?
Programmed cell death - way of recycling bits of cells so there’s not too many. Its constantly occurring.
Where does apoptosis mainly occur?
In G0
What happens during apoptosis?
> nucleus starts dividing and breaking apart
nucleus condenses
cell shrinkage
blebs (bits of cell surface membrane bulging out)
nucleus fragmenting
parts recycled to other cells
rest of cell broken down for parts - phospholipids from membrane
Apoptotic bodies engulfed by phagocyte - gets rid of any waste
Describe morphogenetic apoptosis acting as a stone sculptor - hands
> initially as a foetus the fingers are joined like in a
mitten/puddle
elimination of material by apoptosis
apoptosis occur (told by homeobox genes) and the bits of skin removed from between fingers.
some people have a small amount of skin between fingers - incomplete apoptosis.
What are factors which affect the expression of regulatory genes?
Internal and external factors
> Changes in homeostatic processes - STRESS (Homeostatic stress - constantly cold - environmental stress)
> Drugs - e.g. Thalidamide 1960s-1970s was given to pregnant women to help nausea during morning sickness - messed up homeobox genes - whole generation of babies born without limbs.
