Flashcards in Topic 2 - chapter 8 'Control of gene expression' Deck (36)
housekeeping proteins include...
structural proteins of chromosomes, RNA polymerases, DNA repair enzymes, ribosomal proteins, enzymes involved in glycolysis and other basic metabolic processes, and many of the proteins that form the cytoskeleton
haemoglobin genes only expressed in ...?
Cells generally express between ? & ? genes out of a possible 25000.
5000 and 15000
An example that A Cell Can Change the Expression of Its Genes in Response to External Signals
When liver cell exposed to glucocorticoid hormone - during starvation or intense exercise -> increase prod. of glucose from AA's & other small molecules
T or F - different cell types respond in the same way to same extracellular signals
false - respond in different ways
What are The levels of possible control of gene expression
1. transcriptional control
2. RNA processing control
3. RNA transport & localisation control
4. mRNA degradation control
5. translation control
6. protein activity control
What are regulatory DNA sequences?
a region required for RNA polymerase to bind to the promoter used to SWITCH GENES ON OR OFF
What do regulatory DNA sequences need to work?
proteins called TRANSCRIPTION REGULATORS which bind to DNA
simplest bacterium codes for how many transcription regulators?
Humans code for how many transcription regulators?
Transcription regulators bind to what? Bonds...?
major groove of a DNA helix
bonds include: hydrogen, ionic, and hydrophobic interactions (individually weak but 20 bonds => protein-DNA highly specific & very strong
What are the 3 DNA binding motifs?
homeodomain, the zinc finger, and the leucine zipper
Re. DNA-binding motifs; most of the contacts with the DNA bases are made by
alpha helix 3
In the homeodomain what contacts what?
asparagine contacts adenine
The zinc finger motif is made up of what?
alpha helix & beta sheet bound by zinc (covalently bonded together to allow contact with DNA bases in major groove)
Leucine zipper is made up of what?
2 alpha helixes that bind as dimers
An example of a bacterial transcription switch?
What do activators do?
make promoters stronger
Re. Lac operon, when conditions are +glucose & +lactose
operon off & CAP not bound
Re. Lac operon, when conditions are +glucose & -lactose
operon off, repressor bound & CAP not bound
Re. Lac operon, when conditions are -glucose & -lactose
operon off, repressor bound & CAP bound
Re. Lac operon, when conditions are -glucose & +lactose
operon ON, no repressor & CAP bound => RNA prod.
Eukaryotic activators are bound to what? Describe gene activation at a distance...
enhancers -> looping of DNA to touch mediator & proteins in the vicinity of the promoter incl. RNA polymerase II and general transcription factors
How can proteins allow histones to become more accessible?
activator proteins can recruit histone-modifying enzymes & chromatin-remodeling complexes to promoter region of a gene
Explain how eukaryotic genes are regulated by combinations of proteins
histone-modifying enzymes, chromatin-remodelling complexes, mediator, general transcription factors, RNA polymerase, bound to promoter, also near TATA box, far away are transcription regulators
TATA box is where in relation to start of transcription?
The Expression of Different Genes Can Be Coordinated by a Single Protein. explain...
it's the final number in the combination analogy
glucocorticoid receptor protein with glucocorticoid bound is the last number in the combination
How can combinatorial control create different cells types? eg?
key transcription regulators -> nonmuscle cells to myoblasts by activating changes in gene expression typical of differentiating muscle cells. eg. MyoD in fibroblasts of chick embryo -> muscle cells by induced expression of MyoD gene
What 3 ways can daughter cells 'remember' what cells they're supposed to be?
+ ve feedback loops
DNA methylation (exclusively on cytosine bases) recognised by maintenance methyltransferase