Module 6.1 Flashcards
what is a mutation
a mutation is a random change to the genetic material . Some mutations involve changes to the strucuture or number of chromosomes . A gene mutation is a change to the DNA .
How may mutations occur
mutations may occur spontaneously during DNA replication before cell division . Certain chemicals such as tar in tobacco smoke , and ionising radiation such as UV light , xrays and gamma rays may e mutagenic .
the strucutre of the dna moleucle makes it stable and fairly resistant to corruption of the genetic information stored within it . Errors may occur , howeer during the replicaion od a sna moleucle , what processes is mutation gonna occur in
Mutations associated with meiosis and gamete formation may be inherited by offspirng .
-Gene mutations may affect protein production and funciton.
what are the two main classed of DNA mutation
-point mutation ; one base pair replaces (is substitued for ) another .
-Insertion or deletion (indel) mutation one or more nuclleotides are inserted or deleted from a length of DNA . Thesse may cause a frame shift .
what is a frameshift
alteration to the base sequence of a length of DNAA due to an insertion or deletion of a nucleotide base .
what are point mutations
the genetic code consists of nucleotide base triplets within the DNA .
-During the transcription of a gene , this code is copied to a length of mRNA, as codons , complementary to the base triplets on hte template strands of the length of DNA . The sequence of codons of the mRNA is therefore copy of the sequence of base triplets on the gene (coding of the DNA ) .
what are the three types of point mutation
-Silent
-Missense
-Nonsense
What are point mutations not always causing an effect .
all amino acids involved in protein sumthesis apart from methionine , have more than one base triplet code .
-This reduces the effect of point mutations as the do not always cause a change to the sequence of amino acid in a protein . This is often called redundancy or degeneracy of the genetic code .
What are silent mutations check page 163
A point mutation involving a change to the base triplet , where that triplet still codes for the same amino acid is a silent mutation . The primry structure of the protein and therefore the secondary and tertiary structure is not altered .
what are missense mutations
a change to the base triplet sequence that leads o a change in the amino acid sequence is a missense mutaiton .
-within a gene , such a point mutaiton may have a significnt effect on the protein prpoduced .
-The alteration to the primary structure leads to a change to the tertiary structure of the protein ,altering its shape and prventing it from carrying out its usual funciton .
what are nonsense mutations
a point mutaaiton may alter a base triplet so that it becomes a terminiation stop triplet . This particularly disruptive point mutation resuls in a truncated protein that will not function . This abnromal protien will most likle be degraded within the cell .
what can cause frameshits
both insetions and deetions
explain frame shift in depth (1)
explain frame shift in depth (2)
-This is a frameshift . When the mRNA from such a moated gene is translated the amino acid sequence alter the frameshift is severely disrupted . The primary sequence of the protein , and subsequently the tertiary structure , is much altered . Consequently , the protein cannot carry out its normal function . If the protein is very abnormal , it will be rapidly degraded within the cell .
are all mutations harmful
many mutations are beneficial and have helped to drive evolution hrough natural selection . Different alles of a particular gene are produced via mutation .
examples of netural mutations - neither beneficial or harmful
-inability to smell certain flowers - honeysuckle
different shaped ear lobes
what is an exon
the coding or expressed region of DNA
What is an intron
the non-coding region of DNA
What is an operon
a group of genes that function as a single transcription unit ; first identified in prokaryote cells /
what is a transcription factor
protein , or short , non-coding rna , that combine with a specific site on a length of DNA and inhibit or activate transcription of the gene .
what is the rate that enzymes are catalysed at ?
enzymes that catalyse metabolic reactions involved in basic cellular functions are synthesises at a fairly constant rate.
-Enzymes that may only be needed under specific conditions are synthesised at varying rates according to the needs of the cell .
what is E coili
it normally metabolises glucose as respiratory substrate /
what happens if glucose is absent and the disaccharide lactose is present
lactose induced the production of two enzymes
-lactose permease which allows lactose to enter the bacterial cell .
beta galactosidase which hydrolyses lactose to glucose and galactose .
check figure 1 on page 165 , what is the lac operon
it consists of a length of DNA about 6000 base pairs long , containing an operator region Lac O , next to the structural genes lacZ and lacY , that code for the enzymes beta galactosidase and lactose permease respectively .
what is next to the operator region lac O
it is the promoter region , P , to which the enzyme RNA polymerase binds to begin transcription of the structural genes lacZ and lacY .
what is the control sites
the operator region and the promoter region
what is a small distance away from the operon
it is the regulatory gene , that codes for a repressor protein . When this regulatory gene is expressed the repressor protein produced binds to the operator preventing RNA polymerase from binding to the promoter region .
what does the represor protein prevent
the lacZ and lac Y , from being transcribed ( expressed ) , so the enzymes for lactose metabolism are not made . The genes are ‘off’ .
What happens when lactose is added to the culture medium
once all the glucose has been used , molecules of lactose bind to the Lacl repressor protein preventing it from binding to the operator .
-The RNA polymerase enzyme can then bind to the promoter region and begin transcribing , the structural genes into the mRNA , that will then be translated into the two enzymes . Thus lactose induces the enzymes needed to break it down .
