6.1 Cellular Control Flashcards
Gene mutation
Change in the dna sequence
Mutagen
Anything that promotes a mutation
Point mutation
Substitution
Change in dna sequence
Can be silent, missense or nonsense
Silent
when there’s a mutation which codes for the same amino acid, the mutation is silent because the primary secondary tertiary and quaternary structure will not be changed
Missense
change to the base sequence of DNA that leads to a change in amino acid. Could lead to a harmful protein, non functional protein or a beneficial protein e.g. sickle cell anaemia
Nonsense
New triplet codes for a stop codon
Indel mutations long name
Insertion/deletion mutations
When can Indel mutations be okay
If it occurs in a multiple of 3
What are Indel mutations
When nucleotides are inserted/deleted from gene + bc genetic code is non overlapping the triplets change which causes a frame shift
Are all mutations harmful
No can be beneficial, neutral, non functional
Frame shift
caused by insertion/deletion mutations = cause all further amino acids to be changed including start/stop codons.
Tandem repeats
Repeating triplets at the end of certain genes.
each time the gene replicates through meiosis, the number of triplets increases.
What is the effect of tandem repeats
certain diseases e.g. Huntington can be caused when a threshold is reached
Can genes be switched on
Yes on or off depending on it’s need
Operon
section of DNA that contains cluster of genes that are under the control of a promoter + all transcribed together as well as control elements and a regulatory gene
Intron
non coding region of DNA
Exon
coding region of DNA
Bacteria’s fav source of respiration
Glucose
What do prokaryotic cells do when glucose is absent
Use lactose as a substrate
What enzymes is lactose processed using
Lac y and Lac Z
What does lac y code for
Lactose permease
What does lac z code for
Beta galactosidase
What does lactose permease do
makes cell more permeable to lactose and more lactose can enter to be used
What does beta galactosidase do
breaks down lactose into glucose and galactose
What is lac operon
section of genes that code for enzymes which allows the bacteria to use lactose as a source of energy.
What happens when I is transcribed
Produces a repressor protein which binds to lac o
Lac operon diagram
What happens to lac operon under the presence of glucose
the regulatory gene is transcribed and the repressor protein is made
2. The repressor protein binds to lac O (operator region). This prevent rna polymerase from binding to the promoter region.
3. This prevents the genes Lac z and Lac y from being transcribed
4. The genes are switched off
What happens to lac operon under the presence of lactose and no glucose
I is still transcribed but lactose binds to the repressor protein
1. Under the absence of glucose and the presence of lactose. Lactose binds to the repressor protein. = causes a conformational change
2. This causes a change in shape which prevents it from binding to lac o.
3. This means rna polymerase can bind to the promoter region.
4. This allows Lac z and Lac y to be transcribed. This allows lactose to be metabolised/ the genes are switched on.
Ways eukaryotic cells can change the expression of DNA
- change expression at transcriptional level
- At post transcriptional level
- At post translational level
Transcriptional level modifying
transcription factors = proteins or short non coding pieces of rna so they can slide along the dna and bind to diff promoter regions for diff genes and either suppress transcription or promote transcription
What can transcription factors do
Bind to promoter region + inhibit or allow rna polymerase to bind to the promoter region = either enables or doesn’t allow transcription to occur of the respective gene
Promoter region
control of region of every gene
Why are transcription factors important
Some regulate our cell cycle
Examples of genes involved in regulating our cell cycle + how
tumour suppressant gene and proto-oncogene
Code for transcription factors
What would happen if the tumour suppressant gene and proto-oncogene had a mutation
Cancer
Exon
code for amino acids
Introns
section of a gene that doesn’t code for an amino acid
Post transcriptional modifying
Alternative splicing can produce diff version of mRNA
Removing introns to produce mature mRNA
What is splicing
Removing introns + joining exons together from primary mRNA = produces mature mRNA
Differences in splicing
can join the exons in diff ways which means one mRNA can code for multiple proteins. This all depends on splicing
Splicing enzyme
Endonuclease
Post translational level modification
- When you’ve made your proteins and you wanna switch them on or off
How are enzymes activated
Through phosphorylation
activation of proteins by phosphorylation
using cyclic AMP activates protein kinase A (enzyme that phosphorylated things) = phosphorylated transcription factor to activate it . (Whole lipid transcription factor process) The proteins can be enzymes or transcription factors
Diagram of activation of proteins by phosphorylation
Homeobox genes
codes for transcription factors that code for our body plan
Hox genes
Sub cell of homeobox genes that animals have
codes for transcription factors that code for our body plan
What do hox genes do
controls our axis e.g. how the embryo develops
Mutation in hox gene
Causes problems w development e.g. arms and legs not where they should be
Are homeobox and hox genes highly conserved?
- highly conserved through evolution
- sequence practically same as that from a million years ago
Why are homeobox genes so highly conserved
anytime they’ve been changed, they’re not favoured so important for axis to stay this way
When are homeobox genes expressed
active + expressed really early on + lie themselves on an axis (anterior to posterior/front to back) and they get switched on in an order from anterior to posterior
What do homeobox genes code for
transcription factors e.g. for mitosis and apoptosis
Hayflick constant
limit of how many times a cell can divide before dying. Important bc too many cells leads to tumours
Homeodomain
hox genes have homeobox sequences that code for ‘homeodomauns’. Acts as a transcription factor
What genes regulate hox genes
Gap genes and pair rule genes
What is apoptosis controlled by
- highly controlled process
- internal stimuli (hormones, psychological stress, damage to dna)
- external stimuli (temperature, change in light intensity, pathogen attack, lack of nutrients, drugs)
What does nitric oxide do to apoptosis
Induces it
by making the inner mitochondrial membrane more permeable to hydrogen ions which damages the proton gradient so proteins are released + suppresses the function of apoptotic inhibitor proteins.
Steps of apoptosis
- enzyme breaks down the cell cytoskeleton
- The cytoplasm becomes dense w tightly packed organelles
- The cell surface membrane changes and small protrusions called blebs form
- Chromatin condenses, the nuclear envelope breaks and DNA breaks into fragments
- The cell breaks into vesicles which are ingested by phagocytosis cells = so cell debris doesn’t damage any other cells or tissues
What does apoptosis do
Removes harmful cells
What can too much apoptosis lead to
Cell loss and degeneration
How does failure of the control mechanism during development lead to deformity (hox genes)
Hox gene doesn’t activate transcription factor
Molecules signalling apoptosis not produced
Apoptosis doesn’t occur
Which processes are important in determining body plan of organism
Apoptosis and mitosis
B
C
Shape of antigens on cell surface membrane
State what structural detail of a polypeptide is altered by gene mutations.
Sequence of amino acids
Explain how it is possible for a mutation to have no effect on the protein produced from that gene.
Some triplets code for the same amino acid
So the amino acid sequence isn’t altered
Explain how a mutation could alter the protein so that it no longer performs its correct function in the cell
Insertion will cause frame shift
All triplets down stream will be different
Protein will have diff sequence of amino acids
Tertiary structure will be different
Anatomical
Describe and explain how a tiger with striped fur may have evolved from a non-striped ancestor.
In your answer you should discuss the different types of genes that might be involved in the creation of the striped patter in the tiger’s fur.
Regulatory genes control expression of other genes
Genes switched on or off during development
Recessive Epistasis preventing expression of pigment gene
Mutations = selective pressure of prey availability = adaptation helped tigers camouflage
- striped tigers = greater survival probability = more likely to produce = beneficial allele passed onto next gen
Describe how gene expression can be regulated after transcription.
Primary mRNA modified = removal of introns to produce mature mRNA
Alt splicing can produce diff versions mRNA
Bonds contain energy + can be broken by enzymes
H/OH can form H bonds w water = soluble
Suggest and explain why lactose is unable to cross membranes.
Too big = unable to pass between phospholipids
B produces repressor protein which binds to promoter region and stops transcription
Investigations into the activity of genes that control body plan frequently use fruit flies and mice.
One reason fruit flies are used is that there are fewer public concerns about the ethics of using flies.
Suggest two other reasons why fruit flies are chosen for research into genes controlling the development of body plan.
Low cost
Rapid production
Suggest two reasons why mice are chosen as a suitable species for investigation. Into activity of genes that control body plan
Similar to humans
Low cost
One type of gene is known as a homebox gene.
The base sequences of homeobox genes in humans and chimpanzees are almost identical.
What conclusions about the evolutionary relationship between humans and chimpanzees can be drawn from this piece of evidence?
Little because homeobox genes are highly conserved
Explain why some regions of DNA can be described as ‘non-coding.
Not present in mature mRNA and not translated
Suggest why non-coding regions of DNA show more variation.
Not selected against
