Cell Bio Exam 3 Flashcards
Explain what “crossing over” is in relation to the gene and the chromosome. How is the frequency of a “crossing over” event determined?
The positions of the genes along the chromosome (loci) can be mapped in order along the length of chromosomes based on the crossing over rate. The longer the distance between two loci, the HIGHER the crossing over rate.
The building blocks of a nucleotide are?
A pentose sugar, a phosphate group, and a nitrogenous base.
Where does the information encoded in a DNA nucleotide reside in?
The DNA Base Sequence.
What are different versions of a gene called?
Alleles
A single gene can encode a number of related proteins as a result of a process called…
Alternative splicing
Single-stranded DNA molecules are capable of re-associating with correct base pairing when temperature decreases gradually. What is this property referred to as?
DNA renaturation
What enzyme is responsible for synthesizing mRNAs in the eukaryotic organisms?
RNA polymerase II
What is NOT a normal property of eukaryotic mRNAs?
They reside in the nucleus.
The macromolecular complex that associates with each intron and splices it is called…
Spliceosome
There is only one factor that possesses enzymatic activity in the preinitiation complex for RNA polymerase II. The factor is?
TFIIH
A mature mRNA DOES NOT contain…
Introns
A tRNA has an anticodon with the sequence 5-AUG-3. What would be the sequence of the complementary codon to the normal base pair rule?
3’-UAC-5’
Based on the interchangeability of the nucleotide in the third position. Francis Crick proposed that the same tRNA may be able to recognize more than one codon. What was his proposal called?
The Wobble Hypothesis
What enzyme is responsible for the activation of amino acids?
Aminoacyl-tRNA synthetase
Which of the following is not required for protein synthesis?
Gerneral Transcription Factors
The amino acid bound to the A site tRNA linked to carboxyl carbon of the amino acids are bound to the P site tRNA through?
Peptidyl bonds
What is the significance of the variability of the third nucleotide in a codon?
The same tRNA can recognize more than one codon.
Where does the tRNA bind to during the initiation of protein synthesis?
During initiation of protein synthesis, initiation tRNA binds to “P site” of the ribosome.
The specific site on the bacterial chromosome at which replication begins is called the?
Origin
Replication moves outward from the origin in “___” directions and is said to be “_______”.
1) both
2) Bidirectional
What DNA molecule could serve as an effective template for DNA synthesis?
a partially double-stranded DNA
All DNA polymerases lay down nucleotides in a “______” direction and move along the template in a “_______” direction.
1) 5-3
2) 3-5
The DNA strand growing toward the replication fork grows “________” in a 5-3 direction as the replication fork advances and is called the “_________”.
1) continuously
2) leading strand
During replication, DNA is constructed in small segments call “_______” that are rapidly linked to longer pieces of DNA synthesized earlier.
Okazaki fragments
Strand initiation during replication is carried out by an enzyme that makes a short RNA molecule that is used as a primer; the enzyme is a distinct type of RNA polymerase called?
Primase
Which of the following may be a further advantage of using RNA primers during initiation of a stand in a replication?
Using primers may decrease mistakes; such errors as mismatched…
What proteins bind selectively to single-stranded DNA and are responsible for keeping it extended and preventing it from being rewound?
Single-standed DNA binding (SSB) proteins
What is the function of the 5----3 exonuclease activity of DNA polymerase?
It removes the RNA primer laid down by the primase at the 5` end of the Okazaki fragment.
What is the advantage of transcription-coupled repair?
It ensures that the genes of the greatest importance to the cell receive the highest priority on the repair list.
What must the mismatch repair system be able to distinguish in order to tell which nucleotide of a mismatched pair to replace?
It must be able to distinguish the newly made strand from the parental strand.
Describe what a promoter is and what function it possesses.
A promoter is a region of DNA located upstream of the transcription start site. It has 2 functions:
1) It determines which DNA strand will serve as the template and where transcription will begin
2) It initiates transcription.
List the contents of Mendel’s Law.
Law of Segregation: states that allele pairs separate or segregate during gamete formation, and randomly unite at fertilization
Law of Independent Assortment: states that the alleles of two (or more) different genes get sorted into gametes independently of one another. In other words, the allele a gamete receives for one gene does not influence the allele received for another gene.
Please describe what the functions for the 5 cap and 3 poly A tails.
5’ Methylguanosine cap functions:
- prevents 5’ end of mRNA from being digested by enzymes
- plays an important role in initiating translation
- aids in transporting mRNA out of the nucleus
3’ Poly A tail functions:
- Protects the mRNA from premature degradation by enzymes
List the mutations that can occur in codons.
- A single nucleotide mutation
1) Synonymous: DNA mutation does not change the amino acid sequence
2) Non-synonymous: DNA mutation causes an amino acid substitution
3) Nonsense: DNA mutation creates a premature termination codon - Insertion or deletion mutation:
1) one or more nucleotide(s)
2) A frameshift DNA mutation alters the normal frame of the mRNA
List enzymes required for DNA replication and their functions.
DNA Helicase: Unwinds the DNA double helix
DNA Primase: synthesizes RNA primer
DNA Polymerase: Synthesizes new DNA strand
DNA Ligase: joins fragmented DNA together
DNA Topoisomerase: Changes the supercoiled state of the DNA duplex
According to Watson-Crick Proposal, DNA possesses specific properties. Please list at least 6 properties that were proposed in that proposal. (There are 11 in total to pick from)
- DNA is made of two chains of nucleotides
- The two chains spiral around each other to form a pair of right-handed helices
- The two chains are ANTIPARALLEL (they run in opposite directions)
- The sugar-phosphate backbone is found on the outside of the molecule and the bases are inside the helix
- The double helix is 2 nm wide
- The DNA chains are held together by hydrogen bonds between each base
- Pyrimidines are always paired with purines
- Only A-T and C-G pairs fit within the double helix
- DNA molecule has a major groove (wider) and a minor groove (more narrow)
- The double helix makes a complete turn every 10 residues (3.4 nm)
- The two chains are COMPLEMENTARY to each other
Describe the key steps and the key events of each step in the translation procedure of eukaryotic cells.
Translation happens in three steps:
1) Initiation
- 43S Complex (small subunit) binds to 5’ end of mRNA complex and scans for the AUG start codon
- The 60S (large subunit) joins in after 43S complex reaches the appropriate AUG codon
2) Elongation
- Aminoacyl-tRNAs are selected
- Peptide bonds are formed
- Translocation (the procedure where the ribosome moves of one codon in the 5’ to 3’ direction on the mRNA) happens
- The deacetylated tRNA is released
3) Termination
- happens when one of three stop codons appear
- needs release factor eRF1 to recognize the stop codons
- accompanied by the disassociation of the mRNA from the ribosome and the disassembly of ribosome
