Cellular Control Flashcards
What’s a mutation
A random change to the genetic material
-> the rate of these are increased by mutagens
Gene mutations occur randomly, during DNA replication…
What are the two types of mutation that can occur
- Point
- Indel
What’s a point mutation
When one base pair is substituted for another
Types of point mutations
Silent
Missense
Nonsense
What’s a silent mutation
There’s a change to the base triplet, but the triplet still codes for the same amino acid and the sequence is not changed
-> can occur as generic code is degenerate: certain codons may code for the same amino acid
Therefore, primary / secondary / tertiary structure not affect
What’s a missense mutation
A change to the codon / base triplet, which causes it to become a termination / stop triplet
This results in:
An incomplete polypeptide chain produced, therefore, the protein is shortened & the protein cannot function
What’s an indel mutation
The random insertion or deletion of a nucleotide base pair (not in multiples of 3) into the DNA sequence
-> this can cause frameshifts or the addition / loss of an amino acid
What are the 3 types of indel mutations
Insertion
Frameshift
Deletion
What is an insertion mutation
When the nucleotide is randomly inserted into the DNA sequence. This changes the amino acid that would be coded for
What is a deletion mutation
When a nucleotide is randomly deleted from the DNA sequence. This also changes the amino acid that would be coded for
What is a frameshift mutation
- has a knock on effect of disrupting the reading of codon.
As the genetic code is non overlapping & read as a triplet of bases
Therefore changes all subsequent triplets in the DNA sequence
-> it changes the amino acid sequence produced,
Therefore altering the ability of the protein to function
What happens to abnormal proteins
Degraded in the cell
How can mutations be beneficial
- can result in a characteristic, which offers a selective advantage for the organism
- enhanced function of the protein
How can a mutation be neutral
Can result in a characteristic which offers no selective disadvantage for the organism & no selective advantage either
How can a mutation be harmful
Can result in a characteristic which offers a selective disadvantage for the organism
Malfunctioning protein made
How is gene expression controlled
A regulatory mechanisms which controls it in Eukaryotes = transcription factors
What are transcription factors + their function
Proteins / short non-coding pieces of RNA
Function = attach to DNA @ specific locations
How do transcription factors control which genes turned on / off or activated / suppressed or expressed / not expressed
They do this by
- binding to the genes promoter regions
- preventing RNA polymerase binding to promoter regions
- inhibit, allow RNA polymerase to attach to DNA
- suppress / activate transcription of the gene
Euchromatin vs Heterochromatin
What’s the regulatory mechanism that controls gene expression in prokaryotes
Lac operon
What is operon
A group of genes controlled by the same regulatory mechanism + expressed @ the same time
What do structural genes do
These code for proteins NOT involved in DNA regulation
Structural genes in lac operon
Lac Z & Lac Y
What do Lac Z & Lac Y both metabolise
Lactose
Lac Z -> codes for B galactosidase
Lac Y -> lactose permease
What do regulatory genes, like Lac I, code for
Proteins involved in DNA regulation
E.g. Lac I codes -> repressor proteins
What does the repressor protein Lac I codes for do
Binds to the operator (the DNA sequence that gets binded to)
Therefore, preventing RNA polymerase from binding to the promoter region, therefore genes are off, preventing the transcription of structural genes Lac Z & Lac Y
How does Lac Operon interact when glucose IS present
- regulatory gene (Lac I) expressed, so repressor proteins made & can bind to the operator, blocking the promoter region & preventing RNA polymerase from binding to the promoter region
-> transcription can’t happen so enzymes for lactose metabolism not made
How does lac operon act when glucose is absent + lactose is present
- lactose binds to the repressor protein
-> causing the conformational change in the repressor protein shape
-> so the repressor protein cannot bind to the operator
Therefore:
Promoter region unblocked & RNA polymerase can bind to it
So transcription occurs for structural genes, & enzymes for lactose metabolism are made (e,g, lactose permease, b-galactosidase)
When glucose is present what is lactose released from
The repressor protein
What are introns
Regions of DNA sequence which don’t code for proteins
What are exons
Regions of the DNA sequence that do code for proteins
When is primary mRNA formed
When all of the genes DNA (exons & introns) are transcribed
How is primary mRNA edited
RNA splicing
What’s the process of RNA splicing
Introns removed
Remaining mRNA exons fused together
Form continuous, mature mRNA molecules (ready for translation in the ribosome)
This is important as it ensures only exons of the mRNA are translated to form proteins, therefore, the resulting protein properly has correct function
What happens post transcription after the mRNA is edited, and becomes mature…
Edited further
-> changes into different versions of mRNA
To make proteins with different functions
What are post translational level mechanisms typically regulated by
Activation of proteins by cyclic AMP (cAMP)
other ways include
- protein folding
- addicting non-protein groups
- modifying amino acids to make disulphide bonds
What are post translational level mechanisms typically regulated by
Activation of proteins by cyclic AMP (cAMP)
other ways include
- protein folding
- addicting non-protein groups
- modifying amino acids to make disulphide bonds
How is camp formed
Derived from ATP
Formed by action of enzyme adenyl cyclase
Role of cAMP in lac operon
- if binds to CRP
-> complex bind to RNA polymerase - increases activity of RNA polymerase
- increases efficiency of transcription of structural genes
Role of cAMP in protein kinases
Activates PKA (protein kinase A)
- PKA can then go on to activate other proteins & enzymes
Role of cAMP in protein kinases
Activates PKA (protein kinase A)
- PKA can then go on to activate other proteins & enzymes
What are Homeobox genes
Regulatory genes which control body development (the position of body parts)
- they regulate mitosis & apoptosis in response to internal & external stimuli
- they’re highly conserved in plants, animals & fungi
Examples of body plans Homeobox genes control
- segmentation of organisms into distinct body parts
- development of body parts & organs
- control polarity of the organism (which side is the head versus tail)
What are hox genes
Homeobox genes found in animals, which control body development & determine embryonic body regions along the anterior posterior walls
What is a hox cluster
A group of hox genes
What is the order of hox genes in each cluster is related to
The time & order of the regions in the body that they affect
E.g. 4 limbed vertebrates = 4 clusters
A mutation of Homeobox genes =
A different body arrangement
In Homeobox genes, there are (…) base genes, and (…) amino acids
180
60
What’s the importance of apoptosis & mitosis in cellular control
Too much apoptosis / not enough mitosis -> cell loss + degradation may occur
Too much mitosis / not enough apoptosis -> formation of tumours
Sequence of apoptosis (programmed cell death)
- Enzymes break down cell cytoplasm
- Cytoplasm becomes dense
- Organelles become tightly packed
- Small protrusions called ‘blebs’ form cell surface membrane
- Chromatic condenses
- Nuclear envelope breaks
- DNA breaks into fragments
- Cell breaks into vesicles
- Vesicles ingested by phagocytes
Sequence of apoptosis (programmed cell death)
- Enzymes break down cell cytoplasm
- Cytoplasm becomes dense
- Organelles become tightly packed
- Small protrusions called ‘blebs’ form cell surface membrane
- Chromatic condenses
- Nuclear envelope breaks
- DNA breaks into fragments
- Cell breaks into vesicles
- Vesicles ingested by phagocytes
