Genetics of living systems Flashcards
(30 cards)
Mutation -
Changes in the sequence of the bases of DNA, the change in sequence is caused by substitution, deletion or insertion.
Substitution in a nucleotide -
Changes in the codon which it occurs. This code may form a different amino acid resulting in a difference of the primary structure of a protein. Due to the genetic code being degenerate the new codon may still code for the same amino acid leading to no change in protein synthesis.
Degenerate -
More codons than amino acids therefore amino acids can be coded by more than 1 codon.
The insertion or deletion of a nucleotide leads to -
Frameshift mutation (the triplet code means that the sequence is transcribed consecutively in non-overlapping groups of three)
Effects of different mutations may be -
No effects, damaging or beneficial
No effect of mutation may cause no effect -
No effect on the phenotype because normally functioning proteins are still synthesised.
How can mutations be damaging?
The phenotype of organism is affected negatively because the proteins are no synthesised or fully functional which can interfere with one or more essential processes.
Explain how such rare mutations may be beneficial?
May result in a more useful characteristic in the phenotype, for example mutation in a protein present in the plasma membrane of human cells means HIV cannot bind and enter cells.
Mutations can occur randomly in DNA replication but the rate of mutations can occur because of?
Mutagens
What are mutagens?
Chemical, physical or biological reagent causing mutation.
Genes can be regulated by a number of different factors (Protein synthesis) -
Transcriptional - turned on or off
Post transcriptional - mRNA can be modified which regulated translation and the proteins produced
Translation - stopped or started
Post-translation
Post-translational - Proteins can be modified after synthesis
Operon -
A group of genes that are under control of the same regulatory mechanism and are expressed at the same time. Far more in common in prokaryotes than eukaryotes.
Lac operon is a group of three genes -
Lac z, Lac y and Lac a
What are the genes involved in the lac operon?
Involved in the metabolism of lactose which is a structural gene as they code for three enzymes.
What 3 enzymes does the regulatory gene of lac operon code for?
Beta galactosidase, lactose permease and transacetylase. (transcribed onto a long single molecule of mRNA)
Order of lac operon 1.
Regulatory gene - operator - promoter - structural gene x3 at this point a repressor protein is attached to the operator.
The regulatory gene is located closest to and what does the thing its next to do?
The operator codes for the repressor proteins which.
What does the repressor protein do on the operator -
Prevents transcription of the structural gene in the absence of lactose.
The RNA polymerase cannot bind to the promotor due to -
Repressor protein. Called down regulation
When lactose is present in the lac operon what happens -
It binds to the repressor protein causing it to change shape and cannot complementary fit on the operator, as a result there is space for the promotor region and allows RNA polymerase to bind to it transcribing the structural genes and the enzymes are synthesised.
The process of transcription is relatively slow from the process of the RNA polymerase the required quantity of enzymes produces efficiently is also achieved by another protein binding -
cAMP.
Post-transcriptional factors of RNA processing -
A cap is added to the 5’ end and a tail is added to the 3’ end. Which can be used to stabilise the mRNA and delay the degredation in the cytoplasm.
RNA editing -
The nucleotide of some mRNA can also be changed through the base addition, deletion or submission, this can result in a different range of proteins that can be produced from a single mRNA strand.
Translational control (processes which can be used to regulate processes of protein synthesis) -
Degradation of mRNA - more resistant the molecule the longer it will last in the cytoplasm
