Chapter 19 - Genetics of living systems (Module 6) Flashcards
What is a mutation and what does it disrupt
- change in the sequence of bases in DNA
- Protein synthesis
19.1
What are the 3 different point mutations
substitution, deletion, insertion
19.1
What is a substitution mutation, how can it change an amino acids primary structure and why may it also not.
- changing a base with a different base causing a different sequence in the codon
- can cause a different amino acid to be formed which will affect the R-group interactions within the protein as it may have a different R-group, therefore it will have a different primary structure and can’t function
- the code is degenerate so the new codon may code for the same amino acid
19.1
What are insertion and deletion mutations and why are they called ‘frameshift mutations’
- insertion is when a base is inserted into the sequence and deletion is when a base is taken away from a sequence
- this causes each base to shift meaning every successive codon from the point of mutation may have a different three base sequence
19.1
3 ways a mutations can be silent and have no effect
- occur in non-coding region (intron)
- code same amino acid (degenerate)
- don’t change the overall primary structure
19.1
What is a nonsense mutation and what does it cause
- when a mutations codes for a stop codon
- results in a non-functional protein being synthesised
19.1
what is a missense mutations and what is the difference between conservative and non-conservative mutations
- the incorrect amino acid is synthesised into the primary structure
- conservative : amino acid is similar to original so not severe
- non-conservative : amino acid affects primary structure so has a large effect
19.1
When do mutations commonly occur and what are mutagens
- during DNA replication
- chemical, physical or biological agents which cause mutations
19.1
How does depurination/depyrimdination cause mutation and how do free radicals cause mutation (what negates the effects of free radicals)
- the loss of a purine or pyrimidine base leads to insertion during DNA replication
- free radicals affect the structure of nucleotides so disrupt base paring during DNA replication ( Vitamins A,C and E)
19.1
What is an example of a beneficial mutation
- protein caused by a mutation present in the cell membrane of humans and reject the binding of HIV
19.1
What is a chromosome mutation and what are 4 ways it can occur
- affects the whole chromosome or multiple chromosomes
- Deletion - part breaks off
- Duplication - section is duplicated
- Translocation - section breaks of and rejoins on a different non-homologous chromosome
- Inversion- section breaks of, flips over and rejoins
19.2
What do housekeeping genes and tissue-specific genes code for and why do tissue-specific genes show that gene regulation is required
- enzymes required for metabolic pathways
- protein-based hormones required for growth and development
- gene regulation is required so can control when the genes are expressed as the tissue-specific genes are only required by certain cells at certain times
19.2
What are 3 additional reasons gene regulation is required (2/3)
- each cell with a nucleus has the entire genome including genes not required so regulation is needed so only the genes required by that cell are expressed and not all of them
- this prevents vital resources from being wasted
- in eukaryotes they have to respond to changes in both the external and internal environment so regulation allows cells to specialise and work in a coordinated way
19.2 - Transcriptional control
What is chromatin remodelling ( Heterochromatin and euchromatin ) and how does it allow proteins to be synthesised before cell division
- Heterochromatin - DNA is wound tightly around the histones so DNA can not be transcribed
-Euchromatin - DNA is wound loosely around the histones so the DNA can be transcribed
Euchromatin is present during interphase which allows the essential proteins for cell division to be synthesised in time
19.2 - Transcriptional control
Why does DNA coil around histones and what does acetylation/phosphorylation and methylation cause with the DNA and histones
- histones are positively charged and DNA negatively charged
- acetylation/phosphorylation reduces the positive charge of histones so therefore reducing the attraction and the DNA doesn’t coil as tightly
- methylation - makes the histones more hydrophobic so the histones bind more tightly and therefore DNA coils more tightly
19.2 - Transcriptional control
What is an operon, why is it commonly found in prokaryotes and why is it efficient for saving products
- group of genes under control of the same regulatory mechanism and therefore expressed at the same time
- small and simple structure
- if a certain product isn’t needed then all genes for production can be switched of at the same time
19.2 - Transcriptional control - Lac operon
How does LacI prevent the transcription of the three genes, LacY, LacZ and LacA and therefore prevent the metabolism of lactose in E. coli (4)
1 - LacI codes for a repressor protein
2 - In the absence of lactose this binds to the operator of the lac operon
3 - This prevents RNA polymerase from binding to the promotor of the lac operon
4 - The three genes can not be transcribed by the RNA polymerase
19.2 - Transcriptional control
how does the presence of lactose allow these three genes to be transcribed
- lactose binds to the repressor protein causing it to change shape and therefore stop binding to the operator. This allows RNA polymerase to bind to the promotor and therefore the genes can be transcribed
19.2 - Transcriptional control
How does cAMP affect the rate of transcription of the 3 genes in the lac operon and why does glucose reduce the levels of cAMP
- cAMP allows for the binding of CRP to bind which increases the rate of transcription however is only possible by being bound to the secondary messenger cAMP
- glucose is the preferred substrate of the E.coli so therefore glucose reduces the levels of cAMP and then less lactose is metabolised as transcription is reduced
19.2 - Post transcriptional control
What is mRNA called after transcription compared to before it binds to a ribosome
- pre mRNA and mature mRNA
19.2 - Post-transcriptional control
What 3 things occur at RNA processing, the function of each and where do they occur
- a cap is added to the 5’ end - delays degradation in the cytoplasm as the mRNA is more stable and aids binding to a ribosome
- a tail is added to the 3’ end - delays degradation in the cytoplasm
- Splicing occurs (RNA is cut at specific points) - removes the introns (non-coding sections) and the exons are joined together
19.2 - Post transcriptional control
What occurs during RNA editing and what is the benefit of this
- the nucleotide sequence can be changed through base addition, substitution or deletion
- this increases the range of proteins that can be created by each strand of mRNA
19.2 - Translational control
What 3 factors help regulate the process of protein synthesis (2 slow it down and 1 aids it)
- binding of inhibitory proteins to mRNA prevents it from binding to ribosomes and therefore synthesis of proteins
- degradation of mRNA in the cytoplasm
- initiating factors aid the binding of mRNA to ribosomes - in many organisms eggs make lots of mRNA which are not required but they activate the initiation factors
19.2 - Translational control
What are protein kinases and how do they help regulate cell activity
- enzymes that catalyse the addition of phosphate groups to proteins
- the addition of a phosphate group often activates many enzymes through changing the tertiary structure which therefore can control when enzymes are activated and control reactions
