RNA, DNA, and Transcription
Promoter
A specific nucleotide sequence in DNA that binds RNA polymerase and indicates where to start transcribing RNA.
Polyadenylation
- 250 consecutive A-ribonucleotides, also known as Poly(A) - Added to end of mRNA transcript -Poly(A) Tail - Stabilizes mRNA and helps it from being degraded - The hydroxyl group (-OH) on the 2nd carbon of the sugar ring likes to react with other molecules, making RNA unstable compared to DNA
5' Cap
- 7-methylguanosine (a nucleotide) - Ribosome recognizes 5' cap - Without it, translation will not happen - Stabilizes mRNA
Elongation
- Addition of amino acids to the polypeptide chain - Continues until it reaches a stop codon
Between which molecules in a DNA strand are hydrogen bonds formed?
- Guanine and Cytosine - Adenine and Thymine
CFTR gene
- Is located on chromosome 7 - Contains 188,703 nucleotides long - Contains 27 exons - Codes for a 1480 amino acid protein - Mutations in CFTR result in cystic fibrosis
What is a nucleic acid composed of?
- Phosphate group - Nitrogen containing base - 5-carbon sugar
Transcription Step 3: Termination
- RNA polymerase reaches the terminator - RNA polymerase molecules detach from RNA strand - mRNA detaches from DNA
Transcription
- RNA synthesizes from 5' to 3' end of RNA - Reads DNA 3' to 5' - Error rate= 1 in 10,000 nucleotides
Alternative splicing
- Removal of different introns leads to different proteins produced from one original transcript - This is necessary to have a large diversity of proteins
Sugars
- Ribose (RNA) - Deoxyribose (DNA)
Complementary base pairing
- The association between specific nitrogenous bases of nucleic acids stabilized by hydrogen bonding. - Adenine pairs with thymine ( in DNA) or Uracil ( in RNA) - Guanine pairs with cytosine - The two strands of a DNA molecule have complementary base pairs - The nucleotide sequence of each strand automatically supplies the information needed to produce its partner.
RNA processing
- The modification of mRNA before it leaves the nucleus that is unique to eukaryotes.
Transcription Step 1: Initiation
- Tools: - RNA polymerase - Transcription factors - Where? - Promoter - Eukaryotes (TATA Box) - Separation of the DNA strand forms a transcription bubble
RNA polymerase
-Enzyme similar to DNA polymerase that binds to DNA and separates the DNA strands during transcription - Restores the original DNA strand
A strand of DNA is found to have 30% Cytosine. What % of Guanine does the strand contain?
30% G% must equal C A% must equal T
What would the complementaryRNA transcript message be for 3'-GAG TCT ATT AGC-5'?
5' -CUC AGA UAA UCG -3'
A portion of an exon in the CFTR gene has the sequence:3' GAC TCA CCT CCA GTT CGT 5' What is the correct transcribed mRNA sequence?
5' -CUG AGU GGA GGU CAA GCA -3'
Modification #2
5' Cap
What is the common sequence in the eukaryotic promoter?
5'-TATAAA-3' (TATA box)
If one strand of a DNA molecule has the sequence of bases 5'ATTGCA3', the other complementary strand would have the sequence ________.
5'TGCAAT3'
Transcription factors
Additional proteins that bind DNA and assist RNA polymerase with transcription
Purines
Adenine and Guanine
Nitrogenous bases
Adenine, guanine, cytosine, thymine, uracail
Ribosomal RNA (rRNA)
Aid in translation, found in ribosomes (a protein)
Ribozyme
Any RNA molecule that can act as a catalyst to increase the rate of a chemical reaction
Where does transcription start?
At the promoter DNA (TATA box)
Transfer RNA (tRNA)
Carry individual amino acids into the protein translation complex so they can be added to a growing polypeptide chain
Where does translation occur?
Cytoplasm
Pyrimidines
Cytosine, thymine, uracil
What is the sugar in DNA?
Deoxyribose
What is meant by antiparallel strands of DNA?
Describes the opposite orientation of nucleic acid strands that are hydrogen bonded to one another, with one strand running in the 5' —> 3' direction and the other in the 3' —> 5' direction
Ribosome
Enzyme responsible for protein synthesis
Slipceosome
Enzyme that removes introns
Where does transcription take place?
Inside the nucleus
Why is RNA less stable than DNA?
It has an extra Hydroxyl Group making it more susceptible to hydrolysis
What happens once RNA has been spliced and modified?
It leaves the nucleus and goes to the cytoplasm for translation
A gene in an anteater cell acquired a mutation in the TATA box such that transcription factors (TFs) cannot bind to it. Will transcription take place?
No, because TFs binding to the TATA box initiate transcription in eukaryotes
Introns
Noncoding regions
How does polymerase know when to stop?
Once RNA polymerase sequences through the Poly(A) sequence, it will eventually fall off of the RNA
Modification #3
Polyadenylation
Why does promoter location matter?
Promoter location determines which strand is transcribed
Exons
Protein coding segments of eukaryotic DNA.
Basal transcription factors
Proteins, present in all eukaryotic cells, that bind to promoters and help initiate transcription.
Regulatory RNA
Regulatory role where they can inhibit translation or destroy a RNA transcript
Splicing
Removal of introns
Transcription Step 2: Elongation
Ribonucleotides are added to the 3' end of the growing mRNA strand
What is the sugar in RNA?
Ribose
Eukaryotic transcription and translation is separated in_________
Space and time
Modification #1
Splicing
Hydrolysis
Splitting one molecule into 2 using water
What happens when nucleotides bond together to form a single stranded DNA?
The 3' carbon of the first nucleotide forms a covalent bond with the phosphate group of the next nucleotide
When nucleotides bond together to form a single stranded DNA, which of the following is correct?
The 3' carbon of the first nucleotide forms a covalent bondwith the phosphate group of the next nucleotide
The CFTR gene contains 188,703 nucleotides; the final CFTR mRNA that codes for protein contains 4440 nucleotides. Which of the following do NOT occur to create the final CFTR mRNA?
The spliceosome binds to the CFTR pre-mRNA transcript in the cytoplasm
What pyrimidine does not exist in RNA?
Thymine
Condensation
Two molecules form a bond to become one and water is a product