19.2 Control of Gene Expression Flashcards
What do housekeeping genes code for? (1 mark)
Enzymes that are necessary for reactions present in metabolic pathways, like respiration, are constantly required.
If every cell in an organism contains a complete set of the organism’s genes, why do they have different functions? (1 mark)
Only the genes needed for a cell’s specialised functions are switched on, the rest are switched off.
State 4 ways genes can be regulated. (4 marks)
Transcriptional
Post-transcriptional
Translational
Post-translational
What is a transcriptional factor? (1 mark)
A protein that binds to DNA and switches genes on or off by increasing or decreasing the rate of transcription.
How does a transcriptional factor for a gene that is not to be expressed differ from one that is expressed? (2 marks)
The site on the transcription factor that binds to the DNA is blocked by an inhibitor molecule, so transcription is prevented.
What is heterochromatin, and where is it found in the cell cycle? (2 marks)
Tightly wound DNA
Cell divison
What is euchromatin, and where is it found in the cell cycle? (2 marks)
Loosely wound DNA
Interphase
Describe how chromatin remodelling can affect the transcription of genes. (2 marks)
Transcription of genes is not possible in heterochromatin because RNA polymerase cannot access the gene, but it is possible in euchromatin.
Are histones positively or negatively charged? (1 mark)
Positive
Is DNA positively or negatively charged? (1 mark)
Negatively
What is the relation between DNA and histones? (1 mark)
DNA coils around histones.
How can histones be modified to increase the degree of packing? (2 marks)
Addition of methyl groups, makes them more hydrophobic, DNA coils more tightly.
How can histones be modified to decrease the degree of packing? (2 marks)
Addition of acetyl or phosphate groups, decreases positive charge, DNA coils less tightly.
What is the term for the control of gene expression by modification of DNA? (1 mark)
Epigenetics
What does epigenetics mean? (1 mark)
The control of gene expression by modification of DNA.
What is an operon? (2 marks)
A section of DNA that contains a cluster of genes which are controlled by a single promoter (expressed t the same time).
What is a structural gene? (1 mark)
Codes for useful proteins, like enzymes.
In E.Coli, what substrate is used for respiration when glucose is not available? (1 mark)
Lactose
What is the lac operon? (2 marks)
A group of three structural genes that code for three enzymes and are transcribed onto a single long molecule of mRNA.
What are the three structural genes in the lac operon? (3 marks)
Beta-galactosidase
Lactose permease
Transacetylase
What is a regulatory gene? (1 mark)
Codes for a repressor protein.
What is a repressor gene? (1 mark)
Prevents transcription of the structural genes.
When and how does a repressor gene prevent transcription of the three structural genes in the lac operon? (2 marks)
When lactose is not present.
It binds to the operator, preventing RNA polymerase from binding and transcribing the genes.
What does ‘promoter’ mean? (1 mark)
The section of DNA that the binding site for RNA polymerase.
How is transcription of the lac operon up-regulated? (2 marks)
By cAMP receptor protein (CRP).
The transport of glucose decreases the levels of cAMP and therefore CRP.
What is splicing in the context of changing pre-mRNA to mature mRNA? (1 mark)
Introns are removed and the exons are joined together.
What is RNA processing? (2 marks)
The product of transcription is pre-mRNA, this is modified (by splicing) to form mature mRNA before it can bind to a ribosome and code for the synthesis of the required protein.
What is RNA editing? (2 marks)
When an mRNA molecule is changed through base addition, deletion, or substitution.
State two post-transcriptional controls. (2 marks)
RNA processing
RNA editing
Describe three ways of translational control. (3 marks)
Degradation of mRNA- the more resistant the molecule is the longer it lasts in the cytoplasm.
Binding of inhibitory proteins to mRNA
Activation of initiation factors.
What does an initiation factor do? (1 mark)
Aids the binding of mRNA to ribosomes.
What are protein kinases? (1 mark)
Enzymes that catalyse the addition of phosphate groups to proteins.
Why are protein kinases important? (1 mark)
Many enzymes are activated by phosphorylation, so protein kinases are important regulators of cell activity.
State four ways proteins can be modified after they have been synthesised. (4 marks)
Addition of non-protein groups
Modifying amino acids
Folding or shortening of proteins
Modification by cAMP
Describe how protein kinases can be activated by cAMP. (2 marks)
Binds to cell surface membrane of enzyme, and activates proteins by altering their 3D shape.
This changes the active site of an enzyme to become more or less active.
