Cellular Control 6.1 Flashcards
(33 cards)
What is a phosphodiester bond?
-Covalent bond between sugar of one nucleotide and the phosphate group of the next nucleotide
What does degenerate, non-overlapping and universal?
-Degenerate: more than one codon that codes for each amino acid
-Non-overlapping: each base is only read once
-Universal: same codon codes for same amino acid for all organisms
What is a mutation and what are the three types of mutation?
-A change in the sequence of bases of DNA
-3 types of mutation are:
1.Substitution
2.Deletion
3.Insertion
What is a substitution mutation and the types of ones?
-Substitution= a nucleotide is substituted for another, also known as point mutation
-Different types are Silent mutation(different codon same amino acid), Missense mutation(different amino acid) and Nonsense mutation (stop codon)
What is an insertion and a Deletion mutation?
-Insertion mutation: an extra nucleotide is added
-Deletion mutation: a nucleotide is removed
What is frame shift and what type of mutations cause it?
-Frame shifts happen as a result of indel mutations (insertion and deletion mutations)
-They cause all further amino acids to be changed resulting in a protein that no longer performs its correct function
Exam question: Explain how a mutation could alter the protein so that it no longer performs its correct function in the cell?
- An insertion/ deletion cause frame shift
- All triplets downstream will be different
3.Protein will therefore have a different sequence of amino acids
4.Tertiary structure will be different
What are the different types of changes in chromosome structure?
-Deletion: section breaks off
-Duplication: section duplicated
-Translocation: section breaks off and re-joins
-Inversion: section breaks off, is reversed and joins back on
What is mRNA?
-Made in the nucleus and is small enough to pass through the nuclear pores
-It carries a copy of genetic code for a ribosome in the cytoplasm to make a protein, its bases are Uracil, Guanine, Cytosine and Adenine
What are Structural genes and Regulatory genes?
-Structural genes: code for proteins that have a function within a cell
-Regulatory gene: code for proteins that control the expression of structural genes
What are housekeeping genes and tissue specific genes?
-Housekeeping genes: code for proteins that are constantly required
-Tissue specific genes: code for proteins that are only required at certain times to carry out short-lived response
What are the different ways in which genes are regulated?
-Transcriptional: genes can be turned on and off
-Post-transcriptional: mRNA can be modified
-Translational: translation can be stopped or started
-Post-translational: proteins can be modified after synthesis
What is it called when Chromatin is tightly wound and loosely wound and why is transcription not possible when tightly wound?
-Heterochromatin (tightly wound DNA)
-Euchromatin (loosely wound DNA)
-Transcription is not possible because RNA polymerase cannot access the genes
How does histone modification happen?
-DNA has a negative charge and histones have a positive charge, DNA coils around the histones due to the attractive forces
-Histones can be modified to change the degree of packaging (acetylation, phosphorylation and methylation)
How does Acetylation and Phosphorylation work?
-Both (acetyl and Phosphoryl group) reduce the positive charge of the histone
-This causes the DNA to coil less tightly allowing certain genes to be transcribed
How does Methylation work?
-A hydrocarbon is added making the histone more hydrophobic
-Histone bind more tightly together with DNA, preventing transcription
What are transcription factors and which part of the gene do they bind to?
-Transcription factors are proteins that bind to the promoter region of a gene to control which genes in a cell are turned on and off
What are the two types of transcription of the gene?
-Activators: start transcription by helping RNA polymerase to bind
-Repressors: Stop transcription by blocking RNA polymerase binding
What are tumour suppressor genes and protooncogenes?
-Tumour suppressor genes: genes that inhibit cell proliferation and development
-Protooncogenes: genes involved in normal cell growth which if mutated can cause cancer
How are transcription factors activated?
-Most transcription factors are made inactive
-Hormones can diffuse into cells
-They bind to specific site on inactive transcription factor, changing its shape and activating it, the transcription factor can now move into the nucleus and activate or suppress a gene
When should bacteria express lac operon and what does the gene encode?
-Bacteria should only express lac operon when lactose is available and glucose unavailable
-The lac operon genes encode key enzymes for lactose uptake and metabolism (cause lactose to be used as a substrate instead of glucose)
What do these genes code for and what is the function of their proteins? (Lac Z, Lac Y and Lac I)
-Lac Z codes for the protein B-galactosidase and its function is to hydrolyse lactose to glucose and galactose
-Lac Y codes for the protein lactose permease and its function is to facilitate lactose into cell membrane
-Lac I is a regulatory genes and codes for a repressor gene, the repressor protein prevents transcription of lacZ and LacY in the absence of lactose
When will the lac operon be switched on and off?
-When lactose is present Lac operon is switched on so lac Y and Z are expressed
-When lactose is absent Lac operon is switched off (called down regulation)
What is post-transcriptional regulation?
-The editing of primary mRNA and the removal of introns to produce mature mRNA
