6.1.1 - Cellular Control Flashcards
What are the types of mutation that can occur?
• insertion
• substitution
• deletion
What is substitution?
When one or more bases are swapped / switched for another
What is insertion?
Where one or more bases are added to the sequence
What is deletion?
Where one or more bases are removed for the sequence
What structural effects do mutations have on a protein?
• changes the primary structure - protein it codes for could be altered
• this could change the final 3D shape of the protein so it doesn’t work as it would have originally.
What functional effects do mutations have on a protein?
• neutral effect
• harmful effect
• beneficial effect
What is a neutral effect? Why could it be neutral?
where the mutation doesn’t have an effect on the organism overall
- because the change in base codes for the same amino acid
- because the change in base codes for an amino acid that is chemically similar to the original
- because the change in base codes for an amino acid not involved with proteins function
What is a beneficial effect? Give example
• where the mutation has an advantageous effect on the protein function
• e.g. bacterial enzymes break down antibiotics; mutation changes active site so that they can break down a wider range antibiotics
What is a harmful effect? Give example
• where a mutation has a disadvantageous effect on the function of the protein
• e.g. cystic fibrosis caused by deletion of 3 bases coding for CFTR - folds incorrectly so is broken down so excess mucus builds up in the lungs
Does the location of the mutation on the gene matter?
Yes - if at start of the gene, RNA polymerase can’t bind to gene to start transcription. Loss of production of protein can have harmful defects e.g. genetic disorders.
What are the regulatory mechanisms that control gene expression at transcriptional level?
• Lac Operon in E.coli
• Transcription factors
What are the regulatory mechanisms that control gene expression at post-transcriptional level?
• protein activation via cyclic AMP
• editing of mRNA
How do transcription factors regulate gene expression?
• proteins that bind to DNA to increase rate (activators) or decrease rate (repressors) of transcription to switch genes on and off
• shape of TF determines whether it can bind or not - altered by attaching molecules (e.g. hormones)
• eukaryotes : TF binds to specific DNA sites at start of target gene
• prokaryotes : TF bind to operons
What is an operon?
A group of genes under the control of the same regulatory mechanism and expressed at the same time. Contains: structural genes and control sites.
What are structural genes?
Genes that code for proteins not involved in DNA regulation
What are the structural genes in the Lac Operon?
LacZ, LacY, LacA
What are the enzymes that metabolise lactose?
• Beta-galactoside permease (allows cell to take up more lactose as makes membrane more permeable)
• Beta-galactosidase (enables cell to hydrolyse lactose into glucose and galactose)
What are regulator genes?
Genes that code for proteins involved in DNA regulation
What is the regulatory gene in the Lac Operon?
Lac I
What is the role of Lac I in the presence of ?
A gene that codes for a repressor protein
What is the operator of the Lac Operon?
DNA sequence where repressor protein binds to
What is the promoter of the Lac Operon?
A DNA sequence where RNA Polymerase binds to
What occurs at the Lac Operon in the presence of high glucose levels?
LacI is expressed to code for repressor protein that binds to the operator and blocks the binding site of the promoter.
As DNA polymerase cannot bind to the promoter, transcription cannot occur at LacZ, LacY and LacA
The glucose also decreases the presence of cAMP
What occurs at the Lac Operon in the presence of high lactose?
The lactose binds to the repressor gene, which makes a conformation change to it, causing it to be unable to bind with the operator anymore.
The binding site for the promoter is now clear for RNA polymerase to bind to so transcription of the structural genes can occur
How is the transcription of the structural genes made more efficient in the Lac Operon?
cAMP receptor protein binds to cAMP and upregulates the activity of RNA polymerase
What is chromatin remodelling?
The unwinding of DNA to express a gene to be transcribed
What is heterochromatin?
Tightly wound DNA around proteins called histones so chromosomes are visible under a microscope (this is the case during cell division)
What is euchromatin?
Loosely wound DNA, making the gene readily available to be transcribed (this is to case during interphase)
How do you convert heterochromatin to euchromatin?
To make the DNA become more loosely wound around the histones:
• acetylation - adding an acetyl group to the histones to make them more negative (repelling the DNA away from the histones more)
• phosphorylation - adding a phosphate group to the histones to make them more negative (repelling the DNA away from the histones more)
How do you convert euchromatin to heterochromatin?
To make the DNA become more tightly wound around the histones:
• methylation - adding a methyl group to the histones, increasing the HYDROPHOBIC nature of them (attracting the DNA to wind more closely to the histones)
What is an intron?
A section of DNA that does not code for an amino acid
What is an exon?
A section of DNA that codes for amino acids
What are primary mRNA transcripts?
mRNA strands that contain introns and exons
