6.1 cellular control Flashcards
(25 cards)
What is a mutation
a random change to the genetic material. It involves changes to the structure or number of chromosomes. They occur spontaneously during DNA replication before cell division
what are the two main classes of DNA mutation
-point mutation- one base pair replaces another
-Indel mutation- one or more nucleotides are inserted or deleted from a length of DNA- may cause a frameshift
what are the 3 types of point mutation
-silent
-missense
-nonsense
what is often called the redundancy or degeneracy of genetic code
As all amino acids, apart from methionine, have more than one base triplet code, it reduces the effect of point mutations as they do not always cause a change to the sequence of amino acids in a protein.
what is a silent mutation
a mutation involving a change to the base triplet, where that triplet still codes for the same amino acid. The primary, secondary and tertiary structure of a protein is not altered.
what is a missense mutation
a change to the base triplet sequence that leads to a change in the amino acid sequence in a protein. It alters the primary structure therefore the tertiary structure of a protein, which alters its shape and prevents it from carrying out its usual function.
what does sickle cell anaemia result from
a missense mutation on the 6th base triplet of the gene for the B-polypeptide chains of haemoglobin. Valine is inserted in this position instead of glutamic acid. This results in deoxygenated haemoglobin crystallising within erythrocytes, causing them to become sickle shaped, blocking capillaries and depriving tissues of oxygen
what is a nonsense mutation
when a point mutation alters a base triplet so that it becomes a termination (stop) triplet. This results in a truncated protein that will not function
what are the types of indel mutations
-insertions
-deletions
what is an insertion or deletion
If nucleotide base pairs, not in multiples of 3, are inserted or deleted in the gene, as the code is non overlapping and read in groups of 3 bases, all the subsequent base triplets are altered. This is a frameshift.
What happens when there is a frameshift in a gene
when the mRNA from a mutated gene is translated, the amino acid sequence after the frameshift is severely disrupted. The primary and tertiary structure is much altered. The protein cannot carry out its normal function. If it is very abnormal, it will be rapidly degraded within the cell.
what happens when there is an insertion or deletion of a triplet of base pairs
it results in an addition or loss of amino acid and not in a frameshift
how can mutations be harmful/beneficial
-blue eyes may be harmful in areas where sun intensity is high as the lack of iris pigmentation could lead to lens cataracts/in more temperate zones, it could enable people to see better in less bright light
-humans in Africa would have black skin, the high concentrations of melanin protecting them from sunburn and cancer
-when humans migrated to temperate regions, a paler skin would be an advantage, enabling vitamin D to be made with a lower intensity of sunlight- vitamin D protects from heart disease and cancer
what mutations can be considered neutral
-inability to smell certain flowers, including freesias and honeysuckle
-differently shaped ear lobes
define exon
the coding, or expressed, region of DNA
define intron
the non-coding region of DNA
define operon
a group of genes that function as a single transcription unit
define transcription factor
protein or short non-coding RNA that can combine with a specific site on a length of DNA and inhibit or activate transcription of the gene
what is the lac operon
the control sites and structural genes of E coli
what are the control sites of the lac operon
the promoter region (P)
the operator region (lacO)
what are the structural genes of the lac operon
lacZ- codes for b-galactosidase
lacY- codes for lactose permease
what is I in the lac operon
regulatory gene
describe what happens when E-coli is grown on glucose
when ecoli is grown on glucose, the regulatory gene codes for the repressor protein. The repressor protein binds to the operator region which prevents the RNA polymerase from binding to the promoter region. This means that the mRNA for lactase permease and b-galactosidase cannot be transcribed and therefore cannot be translated meaning the enzymes for lactose metabolism are not made. The genes lacZ and lacY are off. As the e-coli is grown on glucose, it can use it as a respiratory substrate therefore it would be a waste of amino acids and energy to create the enzymes when it can already respire.
describe what happens when E-coli is grown on lactose
when ecoli is grown on lactose, molecules of lactose bind to the lacI repressor protein molecules which alters the shape of the lacI repressor protein therefore preventing it from binding to the operator. Because of this, RNA polymerase can bind to the promoter region and begin transcribing the structural genes into mRNA that will then be translated into B-galactosidase and lactose permease. Lactose Permease increases the uptake of lactose and b-galactosidase hydrolyses lactose to glucose and galactose. Therefore, the ecoli can respire the glucose
