Cellular Control Flashcards
Which types of mutation are inherited and not inherited?
- Mutations associated with with mitosis division (somatic mutations) are not passed to offspring- may be associated w/ development of cancerous tumours
- Mutations associated with meiosis and gamete formation may be inherited by offspring
What are the 3 types of point mutation?
- silent
- missense
- nonsense
What are silent mutations?
- Where the change to the base triplet results in a base triplet which codes for the same amino acid
- Result of the genetic code being degenerate
What are missense mutations?
- A change to the base triplet that leads to a change in the amino acid sequence in a protein
- change in primary structure may have a knock on effect on tertiary structure preventing it from carrying out its usual function
What is an example of an illness caused by a missense mutation?
Sickle cell anemia- mutation on the 6th base triplet on a gene for the polypeptide chains of haemoglobin. Haemoglobin crystallises and deprives tissues of oxygen
What are nonsense mutations?
When a point mutation alters a base triplet so that it becomes a termination triplet/stop codon.
This results in a truncated protein that will not function Which will likely be degraded in the cell
What is an example of an illness caused by a nonsense mutation?
-Duchenne muscular dystrophy
What are indel mutations?
When nucleotide base pairs (not in multiples of three) are inserted or deleted from the gene.
Results in a frame-shift as the code is non-overlapping and read in groups of 3 bases.
Primary sequence of the protein is very effected as well as the tertiary structure- affects function of protein so will likely be degraded in the cell
What is an example of an illness caused by an indel mutation?
Thalassaemia, a haemoglobin disorder
How is Huntington’s disease characterised?
It results from an expanding triple nucleotide repeat if the number of CAG sequences goes above a critical number
What are some examples of non-harmful mutations?
- inability to smell certain flowers
- differently shaped earlobes
- Eye colour, lighter eyes may allow more damage in areas of high sunlight intensity but allow individuals to see better in less bright light
What two enzymes are produced if glucose is absent in prokaryotic cells specifically E. coli?
If disaccharide lactose is present it induces the production of:
- lactose permease: allows lactose so enter the bacterial cell
- B-galactosidase: hydrolyses lactose to glucose and galactose
What does the lac operant consist of?
- Length of DNA containing P/promoter and region next to lacO/operator region: control sites
- This is next to lacZ (codes for B-galactosidase) and lacY (codes for lactose permease): structural genes
- A small distance from the operon is I/the regulatory gene
What is the role of lacZ and lacY?
LacZ- codes for enzyme B-galactoside
LacY- codes for enzyme lactose permease
What is the role of P/promoter region?
It’s where the enzyme RNA polymerase binds to transcribe the structural genes
What is the role of I/the regulatory gene?
- Codes for a repressive protein when expressed; LacI
- LacI binds to the operator region, LacO preventing RNA polymerase from binding to the promoter region
- genes are switched off so enzymes for lactose metabolism are not made
What happens in the lac operon when lactose is added to the culture medium?
- Molecules of lactose bind to LacI altering the shape of the LacI repressor so that it can no longer bind to the operator
- RNA polymerase can then bind to the promoter region to transcribe structural genes
What are transcription factors?
- Found within eukaryotic cells
- proteins or non-coding pieces of RNA which act within the cells nucleus to control which genes are turned on and off/ expressed or not
What are housekeeping genes?
Basic genes expressed in all cells
What are introns?
Non-coding regions of DNA within eukaryotes which are not expressed and separate the coding/expressed regions
What are exons?
The coding or expressed regions of DNA in eukaryotes
Explain the post-transcriptional level of gene regulation in eukaryotes
- All of DNA (both introns and exons) are transcribed -> producing primary mRNA
- endonuclease enzyme involved in editing and splicing, mRNA corresponding to DNA introns are removed, mRNA exons are joined together
What can introns be responsible for after post-transcriptional gene regulation?
They may themselves encode proteins and some may become short, non-coding lengths of RNA involved in transcription
Explain the steps to the post-translational level of gene regulation
- A signalling molecule(eg.hormone glucagon) binds to receptor on membrane of target cell
- Activates a transmembrane protein which activates a G protein
- G protein activates adenyl cyclase enzymes to convert ATP to cAMP
- cAMP activates PKA (protein kinase)
- PKA catalyses the phosphorylation of various proteins hydrolysing ATP in the process and activating enzymes in the cytoplasm(eg. Those that convert glycogen to glucose)
- PKA may phosphorylase another protein which enters the nucleus and act as a transcription factor to regulate transcription
What are homeotic genes?
- Involved in controlling anatomical development/morphogenesis so that all structures develop in the correct location
- Several of these genes contain homeobox sequences/genes
What is a homeobox sequence?
- A stretch of 180 DNA base pairs (excluding introns) encoding a 60-amino acid sequence called a homeodomain sequence.
- Proteins containing these homeodomain sequences are transcription factors
What is the shape of homeodomain-containing proteins? What is the function?
- Can fold into a particular shape; H-T-H, consists of two a-helices (H) connected by one turn (T)
- part of the homeodomain sequence recognises the TAAT Sequence of the enhancer region for a gene to be transcribed
- they bind and therefore regulate the transcription of genes
What are Hox genes? And how to they control body plan development?
- A subset of homeobox genes which are found only in animals not plants
- Regulate the development of embryos along the anterior posterior and control which body parts grow where
What did scientists discover about the nature of homeobox genes?
- Base sequence of homeobox genes in mice and fruit flies were found to be similar
- suggests that homeobox sequences are similar and highly conserved
What will a mutation in a hox gene lead to?
Abnormalities such as antennae on the head or Mammalian eyes on limbs
How are hox genes arranged in tetrapods and mammals?
- There are four clusters of hox genes, each cluster containing up to 10 genes
- At some stage in evolution the clusters have been duplicated
What is colinearity?
When the sequential and temporal order of gene expressions corresponds to the sequential and temporal development of various parts of the body
How are regulators(hox genes) regulated themselves?
By other genes called gap genes and pair-rule genes
Explain the sequence of events during apoptosis
- Enzymes break down the cell cytoskeleton
- Cytoplasm becomes dense w tightly packed organelles
- Cell surface membrane changes, small protrusions called blebs form
- Chromatin condenses, nuclear envelope breaks and DNA breaks into fragments
- Cell breaks into vesicles which are ingested by phagocytes cells so no other cells are damaged by the debris
How is apoptosis controlled?
When genes involved with regulating cell cycle and apoptosis respond to external stimuli such as stress, some signalling molecules can be released by cells.
Eg. Nitric oxide can induce apoptosis by making the inner mitochondrial membrane more permeable to hydrogen ions dissipating the proton gradient. Protons are released into the cytoplasm which bind to apoptosis inhibitor proteins allowing apoptosis to occur
Why is apoptosis necessary for development?
- Proliferation is avoided, without the use of hydrolytic enzymes
- prevents the formation of tumors
- removes ineffective or harmful T-lymphocytes during immune system development
What may too much apoptosis lead to?
Cell loss and degeneration
