DNA & Genetics - Outcome 2 Flashcards
what are the different forms of RNA made in eukaryotic cells?
- mRNA
- tRNA
- rRNA
- snRNA
what is the function of tRNA?
carries anticodons complementary to mRNA sequence and an amino acid specific to the anticodon
what is the function of rRNA?
- brings tRNA and mRNA together
- site of protein production
what is the function of snRNA?
- involved in splicing pre-mRNA to mature mRNA
- has catalytic activity
what is transcription?
process of transferring the genetic information held in the DNA base sequence to mRNA
what is the template DNA strand called in transcription?
antisense strand
how many daughter strands are formed during transcription?
only 1
what is the enzyme that carries out transcription called?
RNA polymerase
what are the 3 stages of transcription?
- initiation
- elongation
- termination
what happens during the initiation phase of transcription?
- one subunit of RNA polymerase attaches to a specific DNA sequence located before the start of the gene (promoter)
- promoter places enzyme at correct place on antisense strand
- affinity between promoter and RNA polymerase subunit is related to frequency with which the gene is transcribed and protein produced
what happens during the elongation phase of transcription?
- RNA polymerase holoenzyme unwinds and ‘unzips’ DNA and builds a strand of mRNA that is complimentary to the antisense strand using free ribonucleotides
- ribonucleotides align alongside complementary nucleotides in DNA strand (hydrogen bonds hold ribonucleotides in place)
- RNA polymerase catlayses phosphodiester bond between ribonucleotides to from RNA strand
what is active RNA polymerase called?
holoenzyme
what are examples of free ribonucleotides?
- rATP
- rUTP
- rGTP
- rCTP
what happens during the termination stage of transcription?
- transcription stops at a specific transcription termination sequence oh the DNA at the 5’ end of gene
- when transcription complete, mRNA transcript detaches from RNA polymerase and forms DNA template strand
- RNA polymerase detaches from DNA - reforms double-helical structure
state the difference between an exon and an intron
- exons are coding regions
- introns are non-coding regions
describe the process of splicing
- a primary transcript of mRNA is processed in the nucleus to remove introns
- further modifications at each end of the primary transcript take place to assist the ribosome in attaching and detaching from the mRNA
- 5’ cap and 3’ poly A tail are added to produce mature mRNA that will exit nucleus and be used in translation in cytoplasm
what is the difference between a promoter with a strong affinity versus a promoter with a weak affinity?
- strong promotes will transcribe more efficiently
- weak promoter will have difficulty attaching to RNA polymerase
what are transcription factors?
- proteins that can bind to DNA in a promoter sequence and increase/decrease likelihood of gene expressing
what is an operon?
a cluster of related DNA
what is the lac operon used for in E. coli?
controlling lactose metabolism
describe what happens in the lac operon if there is an absence of lactose
- repressor gene produces repressor protein
- repressor protein (RP) binds to the operator
- due to RP being bound to operator - RNA polymerase cannot bind to promoter
- structural genes are not transcribed by RNA polymerase
describe what happens in the lac operon if lactose is present
- repressor gene produces repressor protein
- lactose binds to repressor protein, changing conformation so it can no longer bind to the operator
- RNA polymerase binds to promoter
- RNA polymerase transcribes mRNA
- structural proteins are translated from mRNA
what is the inducer molecule of the lac operon?
lactose
describe the action and effect of a transcription factor
- transcription factor binds to promoter and then an enhancer binds on to the transcription factor
- this allows mRNA to be more increasingly transcribed
what are the advantages of an operon?
- saves energy and resources
- increases efficient of transcription
- all related genes under one point of control
what is epigenetic?
study of changes in organisms caused by the modification of gene expression rather than the alteration of the genetic code itself
what factors can influence epigenetics?
- diets
- stress
- exposure to toxins
- pollution
- exercise
- trauma
what are the two main systems involved in causing epigenetic change?
- DNA methylation
- Histone modification
what is the effect on gene expression in the human epigenome if a cytosine ring one DNA is methylated?
- gene expression is repressed/switched off
- methylation prevents transcription from occuring
what is a histone?
- highly alkaline protein
- major component is chromatin
what is the function of a histone?
- package and order DNA
- DNA is wound round histones to form a nucleosome
what happens if histones are acetylated?
histones become less tightly bound to DNA
what happens if histones are deacetylated?
DNA becomes tightly bound to the histone
describe the outcome of epigenetics in twin studies?
- twins exposed to different environmental factors may have different epigenetic tags
- leads them to expressing/repressing different genes
- tag alters phenotype
