Cell Bio Final_Exam 3 Essay_2019 Flashcards
Please describe what is a promoter and what function a promoter possess.
A region of DNA that locates prior to the transcription start site of a gene
- Contains information that determines which of the two DNA strands will be used as the template and where transcription will begin
- Initiates transcription
Please describe what the functions are for the 5’ - cap and 3’ - poly(A) tail.
Function of the 5’-cap:
- Prevents the 5’-end of mRNA from being digested by enzymes
- Aids in transport of the mRNA out of the nucleus
- Plays an important role in the initiation of translation
Function of 3’ poly (A) tails:
- Protect the mRNA from premature degradation by enzymes
Please list the mutations that can occurring the DNA molecule, and briefly explain
what happens for each mutation.
- Ionizing radiation: DNA double-strand break
- Common chemicals: change base of a DNA molecule
- UV radiation: form pyrimidine dimer
- Thermal energy from normal metabolism: Disassociation of A and G from the sugar
List enzymes required for DNA replication and their functions
- Primase: synthesizes of RNA primer
- Helicase: Unwinds the DNA double helix
- Topoisomerase: Changes the supercoiled state of the DNA duplex
- DNA polymerase: Synthesizes new DNA strand
Single stranded DNA binding protein plays critical role during DNA replication.
Please describe what functions it can play.
Function of SSB proteins:
- Prevents reannealing
- Protects ssDNAfrom degradation
- Remove secondary structure from the DNA to allow other enzymes to function effectively
Describe the steps and events of translation procedure in mitotic cells
Initiation
- 43S complex binds to the 5’ end of mRNA complex and scan for the AUG start codon
- Large subunit (60S) joins the complex after 43S complex reaches the appropriate AUG codon
Elongation
The elongation cycle is the process of adding each subsequent amino acid to the growing polypeptide chain.
1. Aminoacyl-tRNAselection
- With the charged amino acid in the P site, the next aminoacyl-tRNAbinds to the vacant A site is the first step for elongation
2. Peptide bond formation
- Catalyzed by peptidyl transferase, Amine nitrogen of the amino acid bound to the A site tRNAlinked to carboxyl carbon of the amino acid bound to the P site tRNAfor the formation of peptide bond
3. Translocation
- Translocation refers to the procedure that ribosome moves three nucleotides (one codon) in the 5’ to 3’ direction on the mRNA molecule
4. Releasing the deacylated tRNA
- The deacylated tRNAleaves the ribosome and empty the E site of the ribosome
Termination
- Termination occurs at one of the three stop codons: UAA, UAG, or UGA
John works in a biological lab where his research if focused on investigating the mechanism of DNA damage repair in mammalian cells. One day he expose the HCT116 cells ( a kind of colorectal cane cells) to the ionizing radiation for 2 minutes, which is long enough to generate DNA damage for the cells. Could you predict: 1) what kind of DNA damage he will observe in the cells; 2) what kind of DNA repair mechanism the cells will use to repair the specific DNA damage?
1) Ionizing radiation (X-ray or gamma rays): which causea a double strand break
2) There are two DSB repair mechanisms: Nonhomologous end joining (NHEJ) , not a faithful repair, and Homologous recombination, a more accurate pathway (HR)
You have set up a cell - free transcription system is a test tube. By mixing DNA, RNA polymerase, sigma factors, ribionuclotides and other essential substances, you are able to make mRNAs identical to those made under a variety of conditions the cells from which these components were isolated. What would happen if you were able to remove the sigma factor first added to the tube and replace it with another sigma factor?
A different set of rRNAs will likely be produced