6.1.1 Cellular Control Flashcards
How can mutations occur?
Insertion, deletion or substitution of one or more nucleotides on a DNA sequence
What are the possible effects of gene mutations?
Neutral
Beneficial
Harmful
Impact whether protein is produced on not
Why do some mutations have a neutral effect?
- The mutation changes a base in a triplet, but aa that the triplet codes for does not change - DEGENERATE CODE
- The mutation produces a triplet that codes for a similar aa, but the aa is chemically similar to original so function is similar to original aa
- The mutated triplet codes for an aa not involved with the protein’s function (e.g. if the affected amino acid is
How do mutations specifically impact proteins?
They can make a protein more or less active by changing the primary structure of the protein if the mutated triplet code no longer codes for the same aa thus the tertiary structure may also change as the proteins fold in a different manner thus the protein does not function properly
E.g. active sites of enzymes may be affected and thus substrates will no longer be able to bind to the active sites
Which type of mutation is most likely to cause a neutral effect?
Substitution
How can mutations be beneficial and give an example?
The mutation can have an advantageous effect on am organism - possibly can ↑ organisms chances of survival
E.g. some bacterial enzymes break down certain antibiotics and mutations in those genes that code for these enzymes could make them work on wider range of antibiotics, making the bacteria antibiotic resistant + thus helping them survive
Mutations that are beneficial to organism are passed onto future generations by process of natural selection
How does beneficial mutation and natural selection work in tandem?
- There is a mutation causing an advantageous trait in an organism
- As the gene is favourable to the organism’s survival, it survives selection pressure (cold winter), whereas non-mutated organism are more likely to die
- Genes with mutations go on to reproduce and process continues where most mutated organisms survive to reproductive age and pass on advantageous allele to their offspring
- Frequency of mutated allele increases from generation to generation
How can mutations be harmful and give an example?
The mutation has a disadvantageous effect on an organism - can ↓ their chances of survival
E.g. 1 -cystic fibrosis is caused by deletion of 3 bases in gene that codes for CFTR protein, thus the mutated CFTR protein folds incorrectly and so is broken down - leads to excess mucus production which affects lungs of CF sufferers
E.g. 2- certain mutation in BRCA1 gene can ↑ risk of breast cancer- the gene produces a protein that helps repair breaks in DNA, but mutations in BRCA1 gene itself can result in a very short protein that cannot do its job and thus may lead to uncontrolled cell division + development of cancer
How do mutations impact whether or not a protein is produced with an example?
If a mutation occurs at the start of gene and so prevents RNA polymerase from binding to start of gene then transcription cannot occur so protein coded for by gene will not be made- can have harmful impacts such as genetic disorders
E.g. HBB gene codes for beta-globin protein, a component of haemoglobin but the genetic disorder beta thalassaemia can be caused by mutation in region of HBB gene where transcription is initiated - mutation here leads to little or no production of beta-globin thus leads to ↓ levels of haemoglobin thus RBC development is disrupted + less O2 can be transported to somatic cells
What is a frameshift mutation?
Adding or deleting a base changes the number of bases present thus causing a shift in all base triplets that follow - an insertion or deletion causes the rest of the base sequence to be read differently
The earlier a frameshift mutation appears in the base sequence, the more aa affected + the greater the mutation’s effect on the protein
BUT if the n.o. of bases added is a multiple of 3 then a FS mutation won’t occur as the triplets that follow will still be read correctly
What can ↑ the rate of mutations?
MUTAGENS
physical- ionising radiation such as x-rays
chemical- deaminating agents
biological- viruses + alkylating agents
What are the 3 regulatory mechanisms for gene expression?
TRANSCRIPTIONAL,
POST-TRANSCRIPTIONAL
POST-TRANSLATIONAL
Explain transcriptional control in eukaryotes?
Gene expression can be controlled by altering the rate of transcription of genes, ↑ transcription means more RNA which can be used to make more protein, this process is controlled by transcription factors which bind to specific DNA sites near the start of their target gene - the genes they control the expression of + then RNA polymerase binds to them
Explain post-transcriptional control in eukaryotes and prokaryotes
Eukaryotes - after transcription, mRNA is edited as genes contain introns, during transcription both introns and exons are transcribed into mRNA which is called PRIMARY mRNA TRANSCRIPTS or pre-mRNA
Introns are then removed by process called splicing - introns removed + exons joined together to form MATURE mRNA strands, which takes place in nucleus
Prokaryotes - mRNA is produced directly from DNA, without splicing as there are no introns in prokaryotic DNA
Explain post-translational control and give an example
Some proteins are not functional straight after translation + need to be activated - which is controlled by molecules like hormones + sugars - some molecules (primary messenger/control molecule) bind to CSM receptors + then trigger the production of cyclic AMP (secondary messenger) which relays message to inside of cell
cAMP is cyclic adenosine monophosphate which alters a proteins 3D structure like an enzyme’s active site making it more or less active
E.g. activation of protein kinase A (PKA) by cAMP, where PKA is an enzyme made of 4 subunits when bound together are inactive - when cAMP binds, it causes a change in its 3D structure, releasing the active sub-units thus PKA is now active
