MCAT BIOLOGY: COMPLETE REVIEW & STUDY
GUIDE
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
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)
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)
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
GUIDE
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
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)
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)
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
