Genes Flashcards
What is a mutation
A mutation is a change in the sequence of bases in DNA.
Caused by a substitution, deletion or insertion of one or more nucleotides
What is a point mutation
When only one nucleotide is affected, one base is incorrectly substituted in place of another base. The codon changes, which could lead to a change in the amino acid coded for
Why could a point mutation be harmless?
Due to the degenerate nature of the genetic code, the new codon may still code for the same amino acid
It may occur in the non coding regions of DNA (introns)
May result in the change of the primary structure but not change the overall structure
What is a frameshift mutation
Caused by insertion or deletion of a nucleotide
It changes every successive codon from the point of mutation
What are the causes of mutations?
Can occur spontaneously during DNA replication
Rate of mutation can be increased my mutagens
Mutagens: X-rays, viruses, free radicals
What are nonsense and missense mutations?
Nonsense- normal codon becoming a stop codon, resulting in a shorter protein formed which is normally non functional
Missense- incorporation of an incorrect amino acid
What are the types of chromosome mutation?
Deletion
Duplication
Translocation (a section of one chromosome breaks off and rejoins on another non- homologous chromosome)
Inversion (a section of a chromosome breaks off, is inverted, then joins back on the same chromosome)
Transcriptional gene regulation
1) Euchromatin is present in interphase, whereas heterochromatin is present during cell division
Euchromatin- loosely wound DNA around the histone
Heterochromatin- tightly wound DNA around the histone
Transcription of genes is not possible when genes are tightly wound as RNA polymerase cannot access the genes- protein synthesis can only occur during interphase
2) Addition of acetyl or phosphate groups on histones reduces their positive charge, causing DNA to coil less tightly
Addition of methyl groups increases the positive charge of the histones, causing DNA to coil more tightly
Access of DNA to control if genes can be transcribed
What is an operon
A cluster of genes that are under the control of the same regulatory mechanism and are expressed at the same time
Why are operons useful in organisms?
They are an efficient way of saving resources as if a certain gene is not required, then all of the genes involved in its production can be switched off
Why is the lac operon needed?
Used in prokaryotes
Glucose is the preferred respiratory substance of the bacteria, but when it is in short supply then lactose must be metabolised
3 structural genes are coded for by the lac operon which help in the metabolism of lactose
Describe the lac operon
Structure: Regulatory gene (Lac I), operator, promoter, Lac Z, Y and A
When glucose is present- the Lac I gene codes for the repressor protein which binds to the operator, this blocks the RNA polymerase from being able to bind to the promoter therefore transcription of regulatory genes cannot occur
When there is a shortage of glucose- Lactose binds to the repressor protein which causes a conformational change in shape, meaning it can no longer bind to the operator region. RNA polymerase is able to bind to the promoter and transcription of the structural genes can occur
What is the role of cAMP
The binding of RNA polymerase results in a slow rate of transcription that needs to be up-regulated
CRP binds to cAMP, which then binds to the RNA polymerase to make transcription more efficient
What happens to levels of cAMP in the presence of glucose?
Levels of cAMP decrease, number of CRP-cAMP complexes binding to RNA polymerase are reduced, reducing the transcription of structural genes needed for the metabolism of glucose
Lactose is released from the repressor protein, causing a conformational change and it binds to the operator once again
Post transcriptional control
The product of transcription is pre mRNA
DNA splicing must occur, removing introns
and exons being joined together
Caps and tails are added at each end of the mRNA to delay degredation in the cytoplasm and make it easier to bind to the ribosomes
RNA can be edited to increase the range of proteins that can be made from a single mRNA
