M6C19 - Genetics of living systems Flashcards
What are mutations?
Changes in the sequence of nucleotides in DNA molecules.
What are insertion/deletion mutations?
Mutations where one or more nucleotide pairs are inserted or deleted from the sequence, causing a frameshift.
What is a point mutation/substitution?
A mutation where one base pair is replaced by another.
What is a nonsense mutation?
A mutation that stops translation early, resulting in a truncated polypeptide due to a premature stop codon.
What is a missense mutation?
A mutation that results in the production of a different amino acid, altering the tertiary structure of the protein.
What is a silent mutation?
A mutation that changes a codon but does not affect the amino acid sequence produced.
What is an example of a beneficial mutation?
A mutation could have advantageous effects and increase an organisms chance of survival (evolution)
What is an example of a harmful mutation?
A mutation in the CFTR protein which causes cystic fibrosis.
What is another example of a harmful mutation?
Sickle cell anaemiais caused by a substitution in the beta-hemoglobin gene, which alters a single amino acid in the protein produced.
At what levels can gene expression be controlled?
Transcriptional (genes can be turned on or off), post-transcriptional (mRNA can be modified which regulates translation and the type of proteins produced) , and post-translational levels (Proteins can be modified after synthesis which changes their functions).
What is the lac operon?
A group of genes that allows E. coli to produce the enzymes that digest the sugar lactose intoglucose and galactose.
Consists of 3 genes: LacZ, LacY, LacA.
What happens in the lac operon when lactose is absent?
-The lac repressor protein, encoded by the I gene, is expressed in the absence or presence of lactose.
-In the absence of lactose, the lac repressor binds to the lac operator site.
-Repressor binding to the operator blocks progression of RNA polymerase.
-Since RNA polymerase is unable to transcribe the lac structural genes, the corresponding proteins are not made.
What happens in the lac operon when lactose is present?
-When lactose is present, the lactose binds to the allosteric site of the lac repressor. This changes the tertiary structure of the repressor protein.
-So the repressor can no longer bind to the lac operator site.
-So, in the presence of lactose, the lac structural genes are expressed. The proteins encoded by the Z and Y genes are required for the metabolism of lactose.
What is the role of the promoter region in the lac operon?
It is the binding site for RNA polymerase to initiate transcription.
Explain the role of cyclic AMP in transcriptional control
-The binding of RNA polymerase still only results in a slow rate of transcription.
-cAMP receptor protein (CRP) increases the rate of transcription - needs to be bound to cAMP first.
-The transport of glucose into an E. coli cell decreases the levels of cAMP, reducing the transcription of the genes responsible for the metabolism of lactose.
What is a transcription factor?
Proteins involved in the process of transcribing DNA into RNA including a wide range of proteins, and initiate and regulate the transcription of genes.
Describe how transcription can be controlled in euakryotes?
-Hormone enters cell and binds to a
transcription factor.
-Transcription factor activated.
-Binds to promoter region.
-RNA polymerase is able to bind.
Describe post-transcriptional mRNA modification:
-Introns and exons are both copied to mRNA during transcription.
-The introns are spliced out of the pre-mRNA using snRNPs, and the exons are joined together creating mature-mRNA. Both processes occur in the nucleus.
-A cap is also added to the 5’ end and a poly-A tail to the 3’ end of the mRNA to stabilise it and delay degradation in the cytoplasm, also aids binding of mRNA.
Explain how proteins are modified after translation:
By:
-The addition of non-protein groups such as carbohydrates, lipids, or phosphates.
-Modifying amino acids and the formation of bonds such as disulphide bridges.
-Folding or shortening of proteins.
Describe the activation of proteins by cyclic AMP at a post-translational level:
Some molecules (hormones) control protein activation by binding to cell membranes and triggering cyclic AMP (cAMP) production.
cAMP activates proteins inside cells by altering their 3D shape.
Eg. PKA
How do transcription factors control gene expression?
By interacting with the promoter sequence of DNA to either initiate or inhibit transcription.
What happens during post-transcriptional control of gene expression?
Editing of the primary mRNA transcript occurs, removing introns and creating a mature transcript of exons.
What is an example of post-translational control of gene expression?
Activation of proteins like adrenaline with the help of cyclic AMP.
What are homeobox genes?
Genes involved in controlling the development of body plans and regulating transcription during development.
-Highly conserved and have little variation between plants, animals, and fungi.
What are hox genes?
(Used interchangeably with homeobox genes)
-One group of homeobox genes that are only present in animals. They are responsible for the correct positioning of body parts.
-The order in which genes appear along the chromosome reflect the order in which their effects are expressed in the organism.
What is apoptosis?
A form of programmed cell death that controls the development of body plans.
What is the role of mitosis in shaping organisms?
Increases the number of cells leading to growth
What occurs during apoptosis?
Enzymes break down the cytoskeleton, DNA, and proteins, leading to cell shrinkage and fragmentation.
What happens to the fragments of a cell during apoptosis?
They are engulfed by phagocytes and destroyed.
What external factors can affect the expression of regulatory genes?
Change in temperature
Intensity of light
What internal factors can affect the expression of regulatory genes?
Release of hormones
Psychological stress
Drugs
