6.1 cellular control Flashcards
define gene mutation
a change to the genetic material
When do mutations occur
they may occur spontaneously during cell replication before cell division
What can cause mutations
tar in tobacco smoke and ionising radiation such as UV light
When do gene mutations occur
during DNA replication
Describe the differences between mutations associated with meiosis and mitosis
Mutations associated with meiosis affect gamete formation and therefore offspring
Mutations associated with mitosis correlate with the development of cancerous tumours
Define point mutation
One base pair is substituted for another
Define indel mutations
One or more nucleotides are inserted or deleted from a length of DNA and may cause a frameshift
What are the types of point mutations
missense nonsense silent
Define silent mutations
A point mutation involving a change to a base triplet where that triplet still codes for the same amino acid so the primary and tertiary structures are not affected and neither is the function of the protein
Define missense mutation
a change in the base triplet sequence that leads to a change in the amino acid therefore affecting the primary and tertiary structure of a protein as well as its function
When do missense mutations not have a major effect on the function of the protein
The base triplet may code for an amino acid with similar r-group properties so it will not affect the tertiary structure and function too much
the amino acid may be located in an area that isn’t functionally important for example it isn’t near the active site in an amino acid
ne nonsense mutation
Apoint mutation may alter the base sequence so that it becomes a termination triplet
What does a nonsense mutation lead to
A truncated protein
Why do indel mutations lead to a severely disrupted amino acid base sequence
If nucleotide bases not in multiples of three are inserted or deleted from the gene, because the code is non-overlapping and read in groups of three, all the subsequent base triplets are altered.
the primary and tertiary structure of a protein will be severely altered and the protein will be unable to carry out its function and be degraded in the cell
Explain the problem with expanding triple nucleotide repeats
Some genes contain a repeating triplet such as -CAG CAG CAG- in an expanding triple nucleotide repeat the number of CAG triplets increases at meiosis and again from generation to generation.
Huntington diseasr results from this - it is hereditary
explain why not all mutations are harmful
Many mutations are beneficial and have helped to drive evolution through natural selection such as blue eyes
Some mutations appear to be neutral being neither beneficial nor harmful such as the inability to smell flowers
Describe the lac operon
a length of DNA that functions as a single transcription unit containing a promoter then operator region next to the structural genes
What is the function of the promoter region
RNA polymerase binds to it to begin the transcription of the structural genes
Describe the funtion of the regulator gene I
It codes for a repressor protein which binds to the operator preventing Rna polymerase to bind to te promoter region
Outline what occurs when E.coli is grown on glucose
B-galactosidase and lactose permease do not need to be made as it is a waste of energy and amino acids because the glucose can be respired
The regulatory gene codes for a repressor protein which binds to the lacO preventing RNA polymerase from binding to the promoter region so transcription doesn’t occur and mRNA isn’t made and translation doesn’t occur so the genes are off
What happens when E,coli is grown on lactose
The repressor proteins shape is changed when lactose binds to it so it can no longer bind t the lacO and RNA polymerase can bind to the promoter region so transcription and translation occur and the genes are on
What is the purpose of beta galactosidase
hydrolyse lactose to glucose and galactose
What is the purpose of lactose permease
increase uptake of lactose
Describe the regulation of gene expression in eukaryotes
RNA polymerase can only attach to the promoter with the help of a transcription factor which is a protein or a short strand of non-coding RNA
Once the transcription factor binds to the promoter region it will either make it easier of harder for RNA polymerase to bind activating or surpressing transcription
Which transcription factor activates and surpreses transcription
surpress - Non-coding RNA
activate - protein
Define introns
non-coding regions of DNA
Define exon
Coding region of DNA
What can introns be used as
Non-coding pieces of RNA - transcription factorn
What do we call mRNA that hasn’t been spliced
primary mRNA
How are many proteins activated
By being phosphorylated
Describe how cAMP activated enzymes and stimulates transcription
A signalling molecule binds to a receptor and acitvates a g protein which activates adenyl cyclase enzymes which convert ATP to cAMP
cAMP activates PKA which catalyses phosphorylation of various proteins by hydrolysing atp in the process which may activate many enzymes, e.g. thos that convert glycogen to glucose
PKA may phosphorylate other proteins such as CREB which can enter the nucleus and act as a transcription factr
Define apoptosis
programmed cell death
How is apoptosis different to necrosis
Doesn’t release hydrolytic enzymes
Describe the process of apoptosis
enzymes break down the cell cytoskeleton
the cytoplasm becomes dense with tightly packed organelles
the plasma membrane changes and small protrusions called blebs form
chromatin condenses, nuclear envelope breaks down and DNA breaks into fragments
The cell breaks into vesicles that are ingested by phagocytosis
Why is apoptosis important
Important in tissue development, causes digits to seperate and removes ineffective or harmful t-lymphocytes
What happens if there is too much apoptosis
cell loss and degeneration
What happens if there is not enough apoptosis
Tumour development
How is apoptosis controlled
By many cell signals including cytokines, hormones, growth factors and nitric oxide
How does nitric oxide induce apoptosis
By making the inner mitochondrial membrane more permeable to H+ ions, dissipating the proton gradient
Proteins are then released into the cytoplasm where they bind to apoptosis inhibitors allowing it to occur
Define morphogenesis
shape design
Which genes cause morphogenesis
homeotic genes
Describe homeotic genes
Subset of homeotic genes are called homeobox genes which contain a 180 base pair length homeobox
What type of gene is the homeobox
Highly conserved
Define conserved genes
Genes that have remained unchanged throughout the evolution of different descendant species
What does the homeobox sequence code for
A specific sequence of 60 amino acids within the synthesised protein called the homeodomain
Describe the structure of the homeodomains
Consists of 3 alpha helices and the 2nd and 3rd helix create a helix-turn-helix
What is the role of the H-T-H in the homeodomain
The H-T-H shape allows the protein to bind to the DNA and act as a transcription factor
What are hox genes
Homeobox genes found in bilateral animals and are involved in the correct positioning of body parts
How are hox genes arranged
In clusters
What happens if a hox gene is mutated
Body part end up developing in the wrong pace on the body - homeotic mutations
How are hox genes expressed
Expressed in early embryonic development along the head-tail axis
spatial linearity and expressed in temporal order - head to tail
Define spatial linearity
The order of the genes matches expression pattern along embryo
Define collinearity
Spatial and temporal arrangement of hox genes so they are expressed head to tail
