Cellular Control, 6.1 Flashcards
Define Mutation
Random change to genetic material
How do mutations occur?
Randomly. Spontaneously. When exposed to certain chemicals. Ionizing radiation.
What happens if the mutations are associated with mitosis?
Somatic. Cancerous tumors.
What happens if the mutations are associated with meiosis?
Inherited by offspring
What can mutations affect?
Production and function
What are Point Mutations?
One base pair replaces another (substitution)
Define degenerate
Amino acids are coded for by more than one triplet
What are Silent Mutations?
There is a change to the triplet but the triplet still codes for the same amino acid. Structure of the protein is not altered.
What are Missense Mutations?
Change in the triplet sequence leads to a change in the amino acid sequence in a protein. Can alter the primary structure and therefore its function.
What are Nonsense Mutations?
Alters the base triplet so it becomes a termination triplet. Results in a protein that will not function - most likely to be degraded.
What disease can Missense Mutations cause?
sickle cell disease - mutation in the haemoglobin gene.
What disease can Nonsense Mutations cause?
Responsible for Thalassemia recessive blood disease - results in anaemia.
What are Indel Mutations?
Nucleotides are inserted or deleted. Causes a frameshift.
What happens if nucleotides are inserted or deleted?
All the subsequent base pairs are altered as base pairs are read in 3’s.
What happens when mRNA is translated after an indel mutation?
The amino acid sequence is disrupted. The primary and tertiary structures are therefore altered. Protein cannot carry out its function.
What happens if bases are deleted?
Bases are read in triplets so all the bases are shifted forwards
What disease can be caused from Indel Mutations?
Tay Sachs disease - autosomnal recessive disorder, deterioration of mental and physical abilities. Lipids are not broken down sufficiently and accumulate in the brain.
What are expanding triplet nucleotide repeats?
Some genes contain a repeating triplet. The number increases at meiosis and again from generation to generation.
What disease can expanding triplet nucleotide repeats cause?
Huntington disease - if the number goes above a certain critical number
What are mutagenic agents?
They increase the frequency of mutations. Physical or chemical agent that changes genetic material eg radiation.
Why are not all mutations harmful?
Some are beneficial and have helped to drive evolution.
How is blue eyes a useful mutation?
Less pigment. In more temperate areas it allows people to see better
How is Black Skin a useful mutation?
In hot countries. There is lots of melanin which protects against sunburn and skin cancer.
How is Pale Skin a useful mutation?
In temperate regions. Vitamin D can be made with a lower intensity of light
How is cell division controlled?
By genes
What are tumour suppressor genes?
Slow cell division
What do tumour suppressor genes do?
Inhibit cell divisions. Prevents tumours developing - maintains cell division rate.
What happens if tumour suppressor gene is inactive?
A tumour can develop
What are Proto Oncogenes?
Stimulate cell division
What do Proto Oncogenes do?
Normally switched ‘on’ when growth factors are detected by protein receptors. Causes relay proteins in the cytoplasm to switch those genes on.
What is an Oncogene?
Mutation causes oncogenes. They are permanently switched ‘on’ - receptor permanently activated, growth factor produced in excessive amounts.
What does it mean when a gene is switched on?
That it is transcribed into mRNA and then translated in a protein. Only a few genes are expressed at one time.
What are the main stages of protein synthesis?
- Transcription - forms mRNA
- Processing of mRNA
- Translation of mRNA - at a ribosome and a polypeptide chain is formed
What does a transcriptional factor do?
Stimulates the gene to start transcription
What is a transcriptional factor?
A protein or short non-coding RNA that combines with a specific length of DNA to inhibit or activate transcription
How does a transcriptional factor work?
They slide along the DNA molecule seeking and binding to specific parts of the promoter sequence. Either aids or inhibits the attachment of RNA Polymerase.
How can the action of transcriptional factor be stopped?
By an inhibitor molecule - bind to it to prevent in from binding to DNA
What is the operon?
Length of DNA made from structural genes and control sites
What are structural genes?
Code for a protein
What are control sites?
Operator and promoter region of DNA
What does bacteria E.Coli normally metabolise?
Glucose
What can bacteria E.Coli metabolise if there is no glucose present?
Lactose
What are inducible enzymes?
Enzymes that are produced only when they’re needed. Adapt to produced enzymes to metabolise certain nutrients.
What does the bacteria need to do in order to metabolise Lactose?
Needs to synthesise Lactose Permease and B galactosidase
What does Lactose Permease do?
Transport protein - lactose can enter the cell
What does B galactosidase do?
Hydrolysis - breaks down lactose to glucose
How long is the lac operon?
6000 base pairs
What is Lac O and what is its function?
Operator site. Control site, switches LacZ and LacY on and off
What is P and what is its function?
Promoter region. This is where RNA polymerase binds to start transcription of LacZ and LacY
What is LacY and what does it do?
A structural gene. Codes for Lactose Permease.
What is LacZ and what does it do?
A structural gene. Codes for B galactosidase
What does I and what does it do?
The regulatory gene. Codes for a repressor protein..
What happens when the regulatory gene is expressed?
- When expressed the repressor protein bidns to the operator region
- Partially covers the promoter region
- Prevents RNA polymerase binding to the promoter region
- LacZ and LacY cannot be transcribed
What happens to the lac operon if lactose present?
- Lactose will bind to the repressor protein
- Alters the shape of the repressor protein so it can’t bind to the operator region
- RNA polymerase can now bind to the promoter region and LacZ and LacY can be transcribed
- Lactose permease and B galactosidase are produced
- E.coli can now take up and hydrolyse lactose, respire and release energy.
What is an exon?
Coding or expressed region of DNA
What is an intron?
Non-coding region of DNA
What is primary mRNA made up of?
All the DNA - both introns and extrons
What happens to primary mRNA?
It’s edited. RNA and DNA introns are removed. RNA and DNA extrons are joined.
What enzyme is involved in the editing process of primary mRNA?
Endonuclease enzyme
What is Post Translational Gene Regulation?
The activation of proteins. Removal of the start codon. Phosphate groups are added (phosphorylation).
Describe the stages of Post Translational Gene Regulation involving cAMP.
- cAMP is formed from ATP
- cAMP activates PkA
- Activated PkA catalyses the phosphorylation of various proteins - hydrolyzing ATP in the process.
- PkA may activate another protein
- This enters the nucleus and acts as a transcription factor.
What is the homeobox gene sequence?
Sequence of 180 base pairs found in genes involved with regulating patterns of anatomical development
What does the homeobox gene sequence do?
- Encodes a 60 amino acid sequence called a homeodomain sequence
- Can fold and bind to DNA regulating transcription
- They are transcription factors
- Can initiate transcription, switch genes on and off
What can homeobox sequences be described as?
Similar and conserved
What is the shape of a homeobox sequence?
H-T-H. Two alpha helixes (H). Connected by one turn (T)
How do we know that the homeobox sequence is highly conserved?
Homeotic genes in a fruit fly were very similar to those in a mouse. Little variation in may regions of the homeobox genes in different organisms
What can mutations in homeobox genes cause?
Changes in the body plan
What are Hox genes?
A subset of homeobox genes found only in animals, formation of anatomical features
What do Hox genes regulate?
Regulate the development of embryos along the anterior-posterior (head-tail) axis
How are Hox genes arranged?
In clusters of up to 10 genes
How many clusters of Hox genes are there in a 4 limbed vertebrate?
4 clusters
When are Hox genes active?
In early embryonic development
How do Hox genes work?
They encode homeodomain proteins - act as transcription factors, promote cell division, apoptosis etc. Sequential and temporal order of gene expressions.
What abnormalities can occur if a Hox gene is mutated?
- Antennae developing as legs on Drosphilia
- Two sets of wings in Drosphilia
- Mammalian eyes developing on limbs
What is the maternal effect of Hox genes?
Embryo polarity
What is the sementation effect of Hox genes?
Polarity of each segment
How is Retintic Acid involved in gene expression?
- Binds to proteins (steroid receptors)
- RA receptor complex mediates gene expression
What can Retinic Acid be use to treat? What is a side effect?
To treat cystic acne. Causes abnormalities eg head and neck malformations.
What are Hox genes regulated by?
Gap genes and Pair rule genes
How is mitosis involved in the development of the body plan?
Regulated by Hox genes so that the new daughter cell contains the full genome. During cell differentiation some of the genes n the cell are ‘switched off’
What are the longest living cells?
Neurones
What are the shortest living cells?
White Blood Cells
What can cell death cause?
- Blockage of an artery leading to the heart causing death of heart muscle cells
- Death of brain cells which can lead to a stroke
What is the name for cell death?
Necrosis
What is Apoptosis?
Programmed cell death - in built self destruct
What stops Apoptosis from constantly occurring in cells?
Signals from other cells stop apoptosis
What are the features of cell death as a result of Apoptosis?
Neat. Tidy. Orderly dismantle organelles and proteins
What are the features of cell death as a result of Necrosis?
Swell and burst spilling lysosomal enzymes. Damage surrounding cells.
Why might Apoptosis need to occur?
- If DNA is damaged
- If cell is infected by a virus
- Cells need to be removed for body parts to form
- Cell is too old
How does a developing embryo use apoptosis?
Can sculpt fingers from a web-shaped hand - removes cells from between fingers.
Describe the different stages of Apoptosis.
- Enzymes break down cell cytoplasm
- Cytoplasm becomes dense with tightly packed organelles
- Cell surface membrane changes and small protrusions called blebs form
- Chromatin condenses, nuclear envelope breaks down as does DNA
- Cells breaks into vesicles which are ingested by phagocytes - no cell debris
What is a disease that can be cause by apoptosis not functioning properly?
HIV - triggers apoptosis and depletes the immune system
What do positive signals do and what is an example?
Mean the cell survives. Growth factor.
What do negative signals do and what is an example?
Signals that start Apoptosis. Oxidants.
What does Nitric Oxide do?
Makes inner mitochondrial membrane more permeable to H+ ions and dissipates the proton gradient
How does apoptosis affect the immune system?
Removes harmful T-lymphocytes during the development of the immune system
How can a mutation affect apoptosis?
If they have damaged DNA they won’t respond to signals. Cells will not undergo apoptosis and will keep dividing to form a tumour.
What happens if there is too much apoptosis?
Cell loss and degenration
What happens if there is not enough apoptosis?
Tumours forming
What are some differences between RNA polymerase and DNA polymerase?
DNA - replication, produces double stranded, semi conservative replication
RNA - transcription, produces mRNA, single stranded
Why has there been little change to homeobox genes?
The genes are very important. A mutation would have big effects and could alter body plan or be lethal.
What are three stop codons?
UAA. UAG. UGA
