MCAT Biology Exam Questions and Answers 100% CorrectMCAT Biology Exam Questions and Answers 100% CorrectMCAT Biology Exam Questions and Answers 100% CorrectMCAT Biology Exam Questions and Answers 100% CorrectMCAT Biology Exam Questions and Answers 100% Co
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Central Dogma - ANSWER - DNA → RNA → Protein
Purines
- which bases?
- how many rings? - ANSWER -
Pyrimidines
- which bases?
- how many rings? - ANSWER - Remember: "Pyrimidine" has a "y" in it; so does "cytosine" and "thymine."
MCAT Biology Exam Questions and
Answers 100% Correct
Central Dogma - ANSWER - DNA → RNA → Protein
Purines
- which bases?
- how many rings? - ANSWER -
Pyrimidines
- which bases?
- how many rings? - ANSWER - Remember: "Pyrimidine" has a "y" in it; so does
"cytosine" and "thymine."
Phosphodiester Bond - ANSWER - Joins one nucleotide to the next; between the 3rd
C of one ribose and the 5th C of the other to create the sugar-phosphate backbone
Directionality of DNA (convention) - ANSWER - 5' → 3'
(but strands are antiparallel, so other strand is opposite)
3' of DNA attached to ... - ANSWER - OH
5' of DNA attached to ... - ANSWER - Phosphate group
DNA composition - ANSWER - 1. Phosphate group
2. 5-Carbon sugar
3. Nitrogenous base (A, T, G, C)
Which nitrogenous bases form 2 hydrogen bonds? - ANSWER - A, T
,Which nitrogenous bases form 3 hydrogen bonds? - ANSWER - G, C
Replisome - ANSWER - Proteins that govern the replication process
Promoter - ANSWER - Required for transcription. Sequence of DNA nucleotides that
signals beginning point for transcription.
Primer - ANSWER - Required for DNA replication
Consensus sequence - ANSWER - Most common promoter sequences; closer the
DNA nucleotides are to the consensus sequence, the more tightly the RNA
polymerase can bind, which leads to more frequent transcription (and vice versa)
Origin of replication - ANSWER - Where replication begins. Prokaryotes have 1;
eukaryotes have many on each chromosome
DNA synthesis: direction of synthesis - ANSWER - 5' → 3'
(the DNA is read 3' → 5')
Steps of replication (5) - ANSWER - 1. Helicase unzips double helix
2. RNA polymerase builds a primer
3. DNA polymerase adds leading/lagging strands
4. Primers removed
5. Okazaki fragments joined
RNA vs. DNA: differences - ANSWER - RNA:
- C2 is oxygenated (has OH)
- Single stranded
- Uses uracil instead of thymine
- Can move through nuclear pores out of nucleus
,DNA
- C2 is deoxygenaged (has H)
- Double stranded (double helix)
- Uses thymine
- Stuck in the nucleus
Transcription - ANSWER - Process of making RNA (rRNA, mRNA, tRNA)
RNA polymerase - ANSWER - Synthesizes RNA in transcription
Transcription: Steps - ANSWER - 1. Initiation - transcription factors, transcription
initiation complex (including RNA pol) finds promoter
2. Elongation - Template/antisense DNA strand is read and complementary RNA
synthesized in 5' → 3' direction (same as DNA synthesis); DNA is read in 3' → 5'
(also same as DNA synthesis)
3. Termination - temination sequence marks end, special proteins dissociate RNA pol
from DNA
Gene regulation - ANSWER - Most occurs at transcription via repressors and
activators, which bind near promoter and affect activity of RNA polymerase
Operon - ANSWER - Entire transcript in a prokaryote; includes multiple genes
(polycistrionic). I.e., lac operon - operator, repressor, genes, promoter, etc.
RNA post-transcriptional processing - ANSWER - pre-mRNA altered in 3 ways:
1. addition of nucleotides
2. deletion of nucleotides
3. modification of nitrogenous bases
5' cap - ANSWER - Added to mRNA as an attachment site in protein synthesis and
protection against degradation by exonucleases. Done with GTP.
, 3' poly A tail - ANSWER - Added to mRNA to protect from exonucleases.
snRNPs - ANSWER - Recognize introns and snip them out
Intron - ANSWER - Non-coding region of mRNA. Is removed by snRNPs (and
spliceosome complexes) and then degraded in nucleus.
Exon - ANSWER - Coding region of mRNA. Remains after activity of snRNPs and
spliceosome. Then exits the nucleus for translation.
DNA denaturation: conditions, effects - ANSWER - Conditions:
1. Salt solution
2. High pH (basic) solution
3. High temperature
Effects:
- Double helix separates because hydrogen bonds are disrupted
- DNA with more G-C pairs (G-C forms 3 H bonds, while A-T has only 2) has a greater
Tm, so takes more energy to melt
Restriction Enzymes - ANSWER - - method bacteria use to protect themselves from
viruses is to cut viral DNA w/these (bacterial DNA is methylated, so differentiated)
- can form recombinant DNA (artificially) using these
Cloning DNA - ANSWER - Recombinant DNA can be placed in bacteria using a vector
(plasmid or virus), then grown. Screened by including an antibiotic resistance gene
and a lacZ gene to find which colonies actually took up the vector.
cDNA - ANSWER - Complementary DNA. Used often in cloning because has no
introns (and therefore is active). Produced in RT PCR from mRNA.
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