6.1.1 Cellular control Flashcards
What are the different methods of mutation?
1) Substitution
2) Deletion
3) Insertion
What is a frameshift mutation?
A change in DNA sequence that causes the whole sequence to shift - all consecutive bases affected
What are the possible effects of mutations?
- Neutral
- Damaging - coding for cancerous or non-functioning protein
- Beneficial - e.g. HIV immunity, lactose digestion
What are four factors that control gene expression at the TRANSCRIPTION level?
- Chromatin remodelling
- Histone modification
- Lac Operon
- cAMP and CAP (Catabolite activator protein)
Describe the role of chromatin remodelling in gene expression
Heterochromatin (TIGHTLY wound DNA) can’t be transcribed - RNA polymerase can’t reach bases.
Euchromatin (LOOSELY wound DNA) are freely transcribed - only present in interphase
Describe the role of histone modification in gene expression
DNA coils around histone proteins (DNA negative, histone positive).
Acetylation and Phosphorylation REDUCE positive charge on histones - bind less tightly to DNA so INCREASED transcription
Methylation makes histones more hydrophobic, bind tighter together, DNA coils tighter so DECREASED transcription
Describe the role of the lac operon in gene expression
Operon of 3 structural genes - lacZ, lacY and lacA, and nearby regulatory gene (lacI) that codes for repressor protein.
Lactose present: binds to repressor protein, released from operator region and RNA polymerase binds to promoter region - transcription occurs
Describe the role of cAMP and CAP in gene expression
Low glucose: cAMP levels HIGH - bind to CAP, enabling binding to CAP site on DNA - FAST transcription
High glucose: cAMP levels LOW, CAP doesn’t bind to DNA - SLOW transcription
What two mechanisms occur at a post-transcriptional level to control gene expression?
- RNA Processing
2. RNA Editing
Describe the role of RNA Processing in gene expression
Modification of pre-mRNA to mature mRNA - introns removed, extrons joined together (splicing). ‘Cap’ added to 5’ end, ‘tail’ to 3’ end - helps stabilise and delay degradation of molecule
Describe the role of RNA Editing in gene expression
Change in sequence via addition, insertion or substitution. Results in generation of multiple proteins from single strand
What four modifications occur in post-translational level that control gene expression?
- Addition of non-protein groups
- Modification of amino acids and bond formation
- Folding or shortening proteins
- Modification/activation via cAMP
Define homeobox genes, and state their role
Codes for a part of a protein that’s highly conserved in plants, animals and fungi (homeodomain). Protein can bind to DNA to switch genes on/off.
E.g. pax6 controls underdevelopment of retina - causes blindness in humans, mice and fruit flies
Describe the role of hox genes
Group of homeobox genes responsible correct positioning of body parts - appear along chromosomes in the order of body parts.
Regulate mitosis and apoptosis.
Define radial symmetry
Organism only has a top and bottom
e.g. diploblastic animals (jellyfish)
Define bilateral symmetry
Organism with a left and right side, as well as head and tail
e.g. most animals
Give an example of an asymmetrical organism
Sponges
Describe the role of apoptosis and mitosis in controlling body form development
Regulated by hox genes
Apoptosis: Removal of unwanted cells and tissues to shape body parts e.g. hands, toes, brain cells
Mitosis: Increase cell count for growth. Cells undergoing apoptosis release chemicals to stimulate mitosis to remodel tissues afterwards
What external stimuli could influence gene regulation?
- Temperature
2. Light Intensity
What internal stimuli could influence gene regulation?
- Hormone release
- Psychological stress
- Intake of drugs
Give an example of a drug affecting gene regulation
Thalidomide given to pregnant women for morning sickness - caused birth defects (shortened limbs)
Currently used as cancer treatment - prevents formation of capillary networks that aid tumour growth
Define a nonsense mutation
Stop codon coded for mistakenly - results in shortened, usually non-functional protein
Define a missense mutation
Incorporation of incorrect amino acid(s) into protein sequence
Define epigenetics
Controlling gene expression through modifying the DNA sequence
Define an operon
Group of genes, expressed at same time, under the control of same regulatory mechanism
Define morphogenesis
Regulation of the pattern of anatomical development within organisms
What’s the difference between diploblastic and triploblastic organisms?
Diploblastic - two primary tissue layers
Triploblastic - three primary tissue layers
