Transcription/translation Flashcards
How many hydorgen bonds between G-C
3
How mnay hydrogen bonds between A-T
2
what is at the 5’ end?
Phosphate group
What is at the 3’ end?
OH group
What are the two strands of DNA?
Antiparallele
Which way are new dna or rna molecules ALWAYS synthesised?
5’-3’
promoter sequence
Region at the start of the gene
terminator seqeunce
stop signal to indicate end of the gene
structural genes
code for proteins that are involved in structre and function
introns
non-coding sections within a gene
exons
coding sections within a gene
What is transcrpition?
Synthesis of RNA from a DNA template
What is translation
Synthesis of a polypeptiide/protein whose specfiic seqeunce of amino acids is determined by the mRNA base sequence.
What does a three base sequence of DNA code for?
Triplet
What des a three base sequence m-RNA code for
codon
What does a three base sequence of tRNa code for
anticodon
What are introns and exon
The coding regions of genes
what happens to exons?
They are both transcribed and translated
What happens to introns
they are only transcribed.
Do bacteria posses introns?
no
What are flanking regions?
regions of DAN on either side of the cooding region of a gene
What are the two flanking regions
Upstream region
Downstream Regiono
Upstream region
Section of DNA befre the start of the coding region (includes promotor sequence
Downstream Region
Located after the end of the coding region of a gene. Includes the end transcrption signal which terminates transcription
What is a promotor?
Control region of upstream region that exists to switch gene on or off
What do promotors have in them
TATA box
What initiates transcription?
RNA polymerase binds to the promoter region
What are promotors like in prokayrotes
- Two essential sequences
- One is recognised by RNA polymerase
- Second is that TATA box where DNA begins to seperate
What is DNA transcribed into
mRNA
Why is it that an organism must make a mobile copy of genetic instructuions?
DNA cannot move outside of the nucleus
where does transcription occue
Euk-Nucleus
Prok-Cytoplasm
Explain the steps in transcription
- RNA polymerase attaches to promotor region (upstream region)
- DNA unwound by RNA polymerase, breaks weak hydrogen bonds now unpaird bases are exposed
- RNA polymerase contructs pre mRNA by collecting free RNA nucleotides
- DNA reforms to make a double helix
What does pre-mRNA contain?
Introns and exons
What direct is RNA transcript assembeled in?
5’-3’
Explain post transcription modification
Enzymes cut out introns from the pre-mRNA and the remaining exons are joined together and a methly cap is adde and a poly-A-tail to the other.
Where does the mRNA go?
Leaves the nucleus via a nuclear pore to perform its functiion at the ribosomes.
What is a codon
three base sequence of mRNA
What number of bases is mRNA translated in
3
What is the start codon for translation?
AUG
When does translation end?
The entire protein is coded for by many codons untill a stop codon is reached
Where are the amino acids needed to make up the protein found?
In the cytosol
Explain the process of translation
mRNA codon is translated the tRNA with the complementary anticodon will pair with the mRNA codon via base pairs
When this happens an amino acid is deposited and a peptide bind forms between the amino acid and the growing polypeptide chain
What is a tRNA molecules
- coiled RNA molecules
- 3-base sequneces
- one end an anticodon and at the other is a region that attaches to one specfic amino acid.
Explain gene regulation in eukaryotes
Cell needs to control which genes are turned off an on at any one time.
Explain gene regulation in bacteria
Repressor proteins prevent the binding of RNA polymerase to keep the upstream flanking region of a gene, therefore keeping the gene turned off.
What is an operon
Functioning unit of genomic DNA containing a cluster of genes under the control of a single regulatory signal or promoter.
Briefly explain the operation of lac operon
- Bacteria use lactose as a food source
- iif there is no lactose present within the cell the repressor proteinn atttaches to the operator sequence and blocks transcriiption
- if lactose enters the cell then it removes the repressor protein and the RNA polymerase can bind to the promotor.
What are homeotic genes?
Regulator genes that play an important role in the embryotic developemtn of vertebrates and insects.
what can adding a double stranded RNA molecule do?
Cause a gene to be slienced
How does RNA inferencing work?
- Add a long dsRNA to the cell
- Enxyme cuts it into short fragment
- These fragments combine with particular proteins to form a RNA-induced silencing complex
- Target mRNA broken down
- By breaking mRNA down the protein encoded by the gene cannot be produced
