Genetics second exam university of Delaware
How do you determine the number of nucleotides required to encode a given number of amino acids?
-20 amino acids found in proteins. -Need at least three sequential nucleotides to encode an amino acid. Each group of three nucleotides encodes one amino acid. Since there are 64 combinations of 4 nucleotides taken three at a time and only 20 amino acids, the code is degenerate
How does replication of the leading and lagging strand differ?
-Leading strand - template continuously copied -Lagging strand - template discontinuously copied in short segments -Lagging Strand synthesis is opposite direction of moving fork.
What is the impact of DNA polymerase's ability to only synthesize DNA in the 5' to 3' direction?
-copies DNA into DNA -Enzymatic activity synthesizes DNA in 5' to 3' direction. -requires a primer -RNA synthesized by Primase -Replication is initiated at defined spots termed origins of replication (ori).
One mole of a double stranded DNA molecule contains 0.2 moles of adenine. How many moles of guanine will be present in the sample?
0.3 moles
The DNA sequence below is an origin of replication: 3' C G A G T A C C T A G G C T G C A 5' The underlined T indicates the position where RNA primase will begin synthesizing RNA. What sequence will be synthesized?
5' A U C C G A C G U 3'
One mole of the RNA extracted from a single-stranded RNA virus contains 0.2 moles of adenine. How many moles of guanine will be present in the sample?
Cannot determine from information provided
What are enhancers and how can they regulate genes that are located up to 100kb away from enhancers
Cis-acting DNA sequences that can increase the transcription of genes. They regulate genes that are located up to 100kb away by forming chromatin loops to bring the enhancer and target gene into proximity
How are codons arranged in a mRNA?
Codons in an mRNA are read during translation, beginning with a start codon and continuing until a stop codon is reached. mRNA codons are read from 5' to 3',
Telomerase is responsible for:
Completing DNA synthesis of the portion of the daughter strand that was the product of the lagging strand synthesis
You identify a novel mutation in which bacteria retain the Okazaki fragments of the lagging strand. The most likely gene harboring the mutation encodes?
DNA ligase
Why is RNA primase required for DNA replication?
DNA polymerase can only only add nucleotides to an existing 3' end of a strand
What enzymatic activity destroys the transforming principle?
DNAase
Define enhancer, proximal control elements, promoter, exon, intron, poly-A signal sequence
Enhancers: are cis-regulatory elements that enable precise spatiotemporal patterns of gene expression during development and are notable for being able to function at large distances from their target genes. •Promoter -attract RNA polymerase -specific site --typically 5' of coding region -Exon - portion of the genome that is found in the mature RNA -Intron - portion of the genome that is transcribed in the precursor RNA, but removed from the mature RNA by splicing.
Why does telomerase need to be active in germ cells?
Germ cells require telomerase to keep chromosomes intact for the next generation
You identify a strain of bacteria in which DNA polymerase lacks 3' to 5' exonuclease activity. This strain is likely to:
Have a significantly increased spontaneous mutation rate.
The transforming principle was demonstrated by:
Heat treating virulent Streptococcus pneumonia and using the extracted material to convert non-virulent S. pneumonia to a virulent strain
Why do telomeres shorten in somatic cells over the course of an individual's lifespan?
In most somatic tissues, telomerase is expressed at very low levels or not at all -- as cells divide, telomeres shorten
What are the consequences of a mutation that eliminates a splice donor or acceptor
Mutations in these sequences may lead to retention of large segments of intronic DNA by the mRNA, or to entire exons being spliced out of the mRNA.
An isolated human population is found that practices cannibalism. Individuals eat the brains of deceased, believing it passes on wisdom of the dead. These individuals typically die in their early thirties. Autopsy reveals patients have severely necrotic cerebellums. A brain extract from affected humans fed to mice causes similar symptoms in the mice. The extract was individually treated with DNAase, RNAase, protease or lipase. Both protease and lipase destroy the agent causing necrosis. The causative agent is likely to be comprised of:
Only protein and lipid.
What is the function of the anticodon and the wobble position of the anticodon?
Pairing of the 5' position of the anticodon is "sloppy" permitting non-canonical pairing with the 3' position of the codon
In the Hershey-Chase experiment, virus T2 was labeled with either radioactive sulfur or radioactive phosphate. They concluded the genetic material must be DNA because:
Phage ghosts still contain radioactive sulfur, while radioactive phosphate was found inside the bacterial cell
What are the roles of primase, helicase, single stranded binding protein and topoisomerase in DNA replication?
Primase catalyzes the synthesis of a short RNA (or DNA in some living organisms) segment called a primer complementary to a ssDNA (single-stranded DNA) template •Helicase - Separate annealed (bound) double stranded DNA - permit access of Primase and DNA polymerase •Single Stranded DNA Binding protein (SSB) binds and stabilized single stranded DNA and prevents reannealing. •Gyrase (Topoisomerase) relieves torsional stress induced by unwinding of DNA •DNA ligase - to covalently bond DNA synthesized to replace RNA primer.
The function of a promoter is to:
Recruit RNA polymerase and direct proper initiation of transcription
The process of synthesizing new DNA from a parental DNA strand is:
Replication
What is the function of ori sequences?
Replication starts at defined regions on the chromosomes called: Ori (origin of replication)
What is the outcome when telomeres reach a critical short length in somatic cells?
Short telomeres may be a signal for cells to senesce
What is the outcome when telomeres reach a critical short length in somatic cells?
Short telomeres may be a signal for cells to senesce (stop dividing)
What is a potential consequence of reactivating the telomerase gene in somatic cells?
Somatic cells that reactivate telomerase in vitro or in vivo become immortal.
RNA polymerase:
Synthesizes RNA in the 5' to 3' direction
Which one of the following statements correctly describes "telomerase"?
Telomerase is an RNA dependent DNA polymerase
What is the origin of the problem for completely synthesizing linear chromosomes? How does telomerase solve this problem?
Telomerase solves the problem of a linear chromosome, preventing the loss of DNA from the 3" end of the chromosome.
What is the function of the mRNA cap and poly A tail.
The 5' cap and 3' poly(A) tail of mRNA are known to synergistically regulate mRNA translation and stability.
What is the process of transcription and what is the directionality associated with transcription?
The DNA encoding gene products are transcribed by protein complexes containing RNA polymerase activity
What is the function of the TATA sequence, and what mechanical role might that sequence play in transcription initiation?
The TATA sequence indicates where a genetic sequence can be read and decoded. The mechanical role the TATA sequence is defines the direction of transcription and also indicates the DNA strand to be read prokaryotes -10 eukaryotes -30
Chargaff's rules state that:
The amount of purines=amount of pyrimidines, the amount of thymine=amount of adenine, amount of guanine=amount of cytosine, amount of A+T does not equal amount of G+C
The lac operon contains three genes encoding enzymes responsible for:
The cleavage of disaccharide lactose into glucose and galactose
If two mutations affecting the same phenotype complement each other then:
The mutations are in different genes
What is the structure of a bacterial operon including the promoter, operator and structural genes?
The operon structure is composed of three elements: the regulatory region, the structural genes, and the terminator.
What is the role of the splice donor and acceptor in splicing?
The splice donor site includes an almost invariant sequence GU at the 5' end of the intron, within a larger, less highly conserved region. The splice acceptor site at the 3' end of the intron terminates the intron with an almost invariant AG sequence.
How do snRNas control splicing?
The spliceosome is composed of particles made up of both RNA and protein. These particles are called small nuclear ribonucleoprotein
What is the role of splice donor and acceptor in splicing
The splicing process itself is controlled by the given sequences, known as splice-donor and splice-acceptor sequences, which surround each exon
Why do telomeres shorten in somatic cells over the course of an individual's lifespan?
as cells divide, telomeres shorten
What is a potential consequence of reactivating the telomerase gene in somatic cells?
cells become immortalized
How can different snRNAs affect gene products
change splicing pattern of mRNA
What is the impact of RNA editing?
changes in the nucleotides of a RNA following transcription
What is the origin of the problem for completely synthesizing linear chromosomes?
chromosomes get shorter with every replication, endless loop of RNA not being copied into DNA of RNA primer
What is the function of sigma factor in bacterial gene regulation?
directs RNA polymerase to genes that its going to transcribe
1. What is the significance of the following attributes of DNA to its function as the genetic material: a. Double stranded and antiparallel b. 5' and 3' ends c. GC and AT base pairing d. The ribose-phosphate backbone e. Hydrogen bonding & hydrophobic interactions
double stranded= stabilizes dna molecule and doubles information in genome Antiparallel= establishes direction and confers directionality ribose phosphate backbone = stitches together dna hydrophilic H bonding =drives base pairing stabilizes dna molecule
What are the different types of RNAs found in eukaryotic cells and what are their functions?
mRNA codes for protein snRna codes for splicing rRNA codes for translation tRNA codes for translation
What is the consequence of a mutation that eliminates a splice donor or acceptor?
prevents splicing
What complex controls splicing and what is "alternative splicing" and what is the overall significance of splicing.
spliceosome During the process of splicing, introns are removed from the pre-mRNA by the spliceosome and exons are spliced back together. If the introns are not removed, the RNA would be translated into a nonfunctional protein.
What is the role of tRNA in translation and what controls the specificity of the amino acids that are bound to their cognate tRNAs?
the tRNA brings amino acids to ribosome the synthase controls specificity and right amino acid is on tRNA
How can alternative promoters, alternative splice sites and alternative poly A sites expand the repertoire of gene products available to a eukaryotic cells
these give rise to different mRNA. change the protein altering 5' and 3' splicing changes protein and how rapidly it is translated
What is the function of the 5'noncoding and 3' noncoding region of an mRNA?
they both affect the half life of RNA and how well ribosome binds to it
How do sRNAs control splicing
they control it by lining up the donor and acceptor site.
How do antigen presenting cells transfer their telomeres to T-cells and what is the impact on the T-cells?
they interact with t cells by cutting telomers wrap them up in membranes spit them out and t cells incorporate them in their telomers extending t cell lifetime
What is happening during the phases of transcription (initiation, elongation, termination, degradation) and how are these manifested in bacteria?
•Prokaryotic -RNA polymerase •Promoter -attract RNA polymerase -specific site --typically 5' of coding region •Elongation -RNA synthesized 5' to 3' •Termination Specific signals for RNA polymerase to stop
Where do the promoters for RNA POL 1, RNA POL II and RNAPOL III reside with respectto the gene?
•RNA polymerase I - synthesizes rRNA •RNA polymerase II - synthesizes mRNA •RNA polymerase III -synthesize tRNA;snRNAs
What is splicing?
•Removal of sequences from internal portions of RNA.
What four nucleotides are used to synthesize ribonucleic acid (RNA)?
•Uracil base replaces Thymine in RNA. •Uracil basepairs with Adenine when DNA is acting as a template directing synthesis of RNA. U,A,C,G
