Unit 6 review
What functional group defines the 3' end of DNA?
A free hydroxyl group defines the 3' end of DNA.
What functional group defines the 5' end of DNA?
A free phosphate group defines the 5' end of DNA
What is a promoter region? Are promoter regions upstream or downstream of the gene?
A promoter region is the site of transcription. It is upstream of the gene
An mRNA sequence reads: 5'- CGAUGCAGA- 3'. Translate this sequence (Assume you are downstream of the start codon. )
Arg, Cys, Arg
List 3 differences between DNA and RNA.
DNA is deoxyribonucleic acid, double stranded, in the double helix shape, and adenine bond to thymine and guanine binds to cytosine. RNA is ribonucleic acid, single stranded, and adenine binds to uracil and guanine binds to cytosine.
Is DNA positively or negatively charged? How could you tell just by looking at a strand of DNA?
DNA is negatively charged because each phosphate group making up the backbone of DNA contains a negatively charged oxygen atom
If an error occurs in DNA replication, how is it fixed?
DNA polymerase will first proofread the DNA bases, If errors still persist, mismatch repair will take place and enzymes will remove and replace the incorrect nucleotides. If segments of DNA are damaged, nuclease can remove segments of nucleotides and DNA polymerase and ligase can work together to correct the errors.
In which stage of the cell cycle does DNA replicate?
DNA replicates in the S phase of the cell cycle.
True or false: the genetic code is read in groups of two nucleotides at a time called the doublet code.
False
Describe step-by-step how DNA is replicated.
First, DNA replication begins when the DNA is opened at an origin of replication. Next, helicase will unzip DNA strands at the replication fork and single stranded binding proteins will bind to the DNA to keep it open. The enzyme topoisomerase will prevent supercoiling and strain of the replication fork ahead of helicase. Primase will begin adding RNA primers to the parental DNA, which serves as a foundation for where DNA synthesis can begin. Next, DNA polymerase III will attach to the primers on the parental DNA and move in a 3' to 5' direction and add new nucleotides to the new strand in the 5' to 3' direction. Since DNAP III moves in the opposite direction as helicase on the lagging strand, Okazaki fragments will be synthesized, whereas the leading strand is synthesized in a continuous segment. Finally, DNA polymerase I will replace the primers with free DNA nucleotides. DNA ligase will connect the Okazaki fragments.
What does it mean that DNA strands are antiparallel?
If DNA strands are antiparallel, it means that one strand runs from 3' to 5' direction and the other strand runs in the opposite direction, from 5' to 3'
Describe the consequences of a chemical that prevents the 5' cap and poly-A tail from forming on eukaryotic mRNA?
If a chemical prevents the 5' cap and poly-A tail from forming on eukaryotic mRNA, then mRNA will likely undergo degradation.
What would be the immediate effect to transcription if a cell was exposed to a drug that mutated the promoter region?
If the promoter region was mutated, RNA polymerase may not be able to bind there, and if that happened, transcription would not occur. If transcription does not occur, then translation is not occurring.
Why do introns exist if they are just spliced out of the mRNA during pre-mRNA modifications?
Introns play an important role in the process of alternative splicing. This is when an mRNA is spliced to form different protein variants
The DNA from a certain plant species is analyzed. The DNA contains 22% thymine. Determine the percent of the other bases.
It would be 22% adenine, 28% cytosine, and 28% guanine.
Think back to Unit 1. Identify the major classes of macromolecules and then identify their monomers and polymers.
Lipid, proteins, nucleic acids, carbohydrates are the four classes of macromolecules. Lipids' monomers are glycerol and fatty acids, and they are not considered to have true polymers. Proteins' monomers are amino acids, and their polymers are polypeptides. Nucleic acids' monomers are nucleotides, and their polymers are RNA and DNA. Carbohydrates' monomers are monosaccharides, and their polymers are polysaccharides
Differentiate between purines and pyrimidines.
Purines are nucleotides with a double ring structure of one six carbon ring fused to a five-carbon ring. Adenine and guanine are purines. Pyrimidines have a single ring structure and include cytosine, uracil, and thymine.
Why is redundancy in the genetic code important?
Redundancy in the genetic code helps to minimize harmful effects that incorrectly placed nucleotides can have on translation/protein synthesis
Describe the Meselson and Stahl experiment that supported the semi-conservative model of DNA replication.
The Meselson and Stahl experiment consisted of three stages. First bacteria were cultured with a heavy isotope called N15. Then the bacteria were transferred to the medium with N14, a light isotope, and was permitted to replicate. The DNA was then centrifuged and analyzed after each replication. When the bacteria were analyzed, it produced a pattern. G0 only produced bacteria with N15 DNA. G1 also only produced N15 bacteria. However, in G2, the bacteria produced were 100% intermediate, further supporting the semiconservative model
What is the backbone of DNA composed of?
The backbone of DNA is composed of sugar and phosphate
What is the center of DNA composed of?
The center of DNA is composed of paired nucleotides that run antiparallel to one another.
If one DNA strand reads: 3'- ACTAG -5' what would the other strand read?
The complementary strand would read 5'-TGATC-3'
The very first tRNA will enter at which site on the ribosome (A, P, or E)?
The first tRNA will enter at the P site.
If the tRNA anticodon reads 3'- CUU -5' then what does the mRNA codon read that it can bind to? Knowing this, what amino acid will the tRNA be carrying? (Remember: the amino acid the tRNA carries is based on the mRNA codon.)
The mRNA codon reads 5'- GAA - 3'. The tRNA will be carrying Glutamic acid.
Summarize the purpose of translation in 1-2 sentences
The purpose of translation is to translate the sequence of mRNA and synthesize it into proteins.
Referring to question 3, which amino acid does this tRNA carry?
The tRNA carries the amino acid methionine.
Referring to question 3, what is the codon that the tRNA binds to?
The tRNA will bind to the codon AUG.
List and describe the steps of transcription.
There are three stages in transcription. First is initiation. Initiation begins when RNA polymerase attaches to a promoter region of the DNA (in eukaryotes the promoter region is called the TATA box and in prokaryotes, it can bind directly to the promoter region.) Next, elongation occurs when RNA polymerase opens the DNA and reads the triplet code of the template strand. RNA polymerase moves downstream, and the mRNA strand peels away from the DNA template strand. Finally, termination occurs. In prokaryotes, transcription proceeds through a termination sequence in which RNA polymerase detaches and mRNA transcript is released to translation without any type of modification. In eukaryotes, RNA polymerase transcribes a sequence of DNA called the polyadenylation sequence and releases the pre-mRNA from the DNA. It must then undergo modifications before it can be translated. The modifications that pre-mRNA must go through are the addition of a 5' cap, the addition of a poly-A tail, and RNA splicing.
In eukaryotic cells where does transcription occur?
Transcription occurs in the nucleus for eukaryotic cells
Where does translation occur?
Translation occurs at the ribosomes in the cytoplasm for both prokaryotes and eukaryotes, and also at the ribosomes on the RER in eukaryotes.
True or false: only the template strand of DNA is transcribed during transcription.
True
Using a codon chart determine what UAU codes for?
UAU codes for the amino acid Tyr, tyrosine
Fill in the blanks: tRNA has an ________ region which is complementary and antiparallel to _______.
anticodon , mRNA
Fill in the blank: the mRNA nucleotide triplets are called _________. These code for ________ _________.
codons , amino acids
A section of the template strand of DNA reads: 5'-CAACACTAA- 3'. Determine the mRNA sequence and translate it. (Assume you are downstream of the start codon.)
mRNA: 5' - UUAGUGUUG - 3', translated: Leu, Val, Leu. **Remember mRNA is read 5' to 3' so you first have to flip the directionality of the template DNA strand (aka just read it backwards).
Fill in the blanks: protein synthesis occurs in two stages _______ and _________.
transcription , translation
The process of ________ converts DNA to RNA. The process of ______ turns RNA into proteins.
transcription , translation
True or false: plasmids replicate separately from chromosomal DNA.
true
