Cellular Control 6.1 Flashcards
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
What is an intron, Exon and splicing?
-Intron= section of a gene that does not code for an amino acid
-Exon=section of a gene that does code for amino acids
-Splicing= introns are removed and the functional exons are joined together in pre-mRNA
Describe the process of upregulating lac operon?
- No glucose, so lots of cAMP binds to CRP which binds to DNA.
- This helps RNA polymerase bind to promoter region and increases the transcription of lacZ and lacY
What are homeotic genes and homeobox genes?
-Homeotic genes= are genes that regulate morphogenesis (the process that causes an organism to form its shape)
-Homeobox genes= one group of homeotic genes found in all multicellular organisms
Why is a homeobox sequence said to be highly conserved?
-This sequence has been kept through evolution and is the same for many organisms
What are Hox genes?
-A class of homeobox genes found in animals, they regulate the development of embryos along the head-tail axis, ensuring body structures develop in the correct places
What is Apoptosis?
-Apoptosis= programmed cell death in development, it is a series of biochemical events leading to a tidy cell death
What genes regulate mitosis and apoptosis in animals during development?
-Hox genes
-They use both processes to shape body parts
Describe the stages of Apoptosis?
1.Enzymes break down the cell cytoplasm
2. Cytoplasm becomes dense with tightly packed organelles and cell surface membrane changes
3.Chromatin condenses, nuclear envelope breaks down and DNA breaks down into fragments
4.Cell breaks into vesicles that are ingested by phagocytotic cells.
