MEDICAL COLLEGE ADMISSION TEST (MCAT)
LIFE SCIENCES AND MEDICAL PREPARATION
BIOLOGICAL AND BIOCHEMICAL FOUNDATIONS OF LIVING SYSTEMS
BIOLOGY PRACTICE EXAMINATION 2026
SPRING SEMESTER EXAM [2025/2026]
Origin of replication
Where replication begins. Prokaryotes have 1; eukaryotes have many on each chromosome
DNA synthesis: direction of synthesis
5' → 3'
(the DNA is read 3' → 5')
Steps of replication (5)
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
1
RNA vs. DNA: differences
Page
, 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
Process of making RNA (rRNA, mRNA, tRNA)
Promoter
Required for transcription. Sequence of DNA nucleotides that signals beginning point for transcription.
Primer
Required for DNA replication
Consensus sequence
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)
2
Page
, RNA polymerase
Synthesizes RNA in transcription
Transcription: Steps
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
Most occurs at transcription via repressors and activators, which bind near promoter and affect activity
of RNA polymerase
Operon
Entire transcript in a prokaryote; includes multiple genes (polycistrionic). I.e., lac operon - operator,
repressor, genes, promoter, etc.
RNA post-transcriptional processing
pre-mRNA altered in 3 ways:
1. addition of nucleotides
2. deletion of nucleotides
3. modification of nitrogenous bases
3
Page
5' cap
, Added to mRNA as an attachment site in protein synthesis and protection against degradation by
exonucleases. Done with GTP.
3' poly A tail
Added to mRNA to protect from exonucleases.
snRNPs
Recognize introns and snip them out
Intron
Non-coding region of mRNA. Is removed by snRNPs (and spliceosome complexes) and then degraded in
nucleus.
Exon
Coding region of mRNA. Remains after activity of snRNPs and spliceosome. Then exits the nucleus for
translation.
DNA denaturation: conditions, effects
Conditions:
1. Salt solution
2. High pH (basic) solution
3. High temperature
Effects:
4
Page
- Double helix separates because hydrogen bonds are disrupted
LIFE SCIENCES AND MEDICAL PREPARATION
BIOLOGICAL AND BIOCHEMICAL FOUNDATIONS OF LIVING SYSTEMS
BIOLOGY PRACTICE EXAMINATION 2026
SPRING SEMESTER EXAM [2025/2026]
Origin of replication
Where replication begins. Prokaryotes have 1; eukaryotes have many on each chromosome
DNA synthesis: direction of synthesis
5' → 3'
(the DNA is read 3' → 5')
Steps of replication (5)
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
1
RNA vs. DNA: differences
Page
, 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
Process of making RNA (rRNA, mRNA, tRNA)
Promoter
Required for transcription. Sequence of DNA nucleotides that signals beginning point for transcription.
Primer
Required for DNA replication
Consensus sequence
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)
2
Page
, RNA polymerase
Synthesizes RNA in transcription
Transcription: Steps
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
Most occurs at transcription via repressors and activators, which bind near promoter and affect activity
of RNA polymerase
Operon
Entire transcript in a prokaryote; includes multiple genes (polycistrionic). I.e., lac operon - operator,
repressor, genes, promoter, etc.
RNA post-transcriptional processing
pre-mRNA altered in 3 ways:
1. addition of nucleotides
2. deletion of nucleotides
3. modification of nitrogenous bases
3
Page
5' cap
, Added to mRNA as an attachment site in protein synthesis and protection against degradation by
exonucleases. Done with GTP.
3' poly A tail
Added to mRNA to protect from exonucleases.
snRNPs
Recognize introns and snip them out
Intron
Non-coding region of mRNA. Is removed by snRNPs (and spliceosome complexes) and then degraded in
nucleus.
Exon
Coding region of mRNA. Remains after activity of snRNPs and spliceosome. Then exits the nucleus for
translation.
DNA denaturation: conditions, effects
Conditions:
1. Salt solution
2. High pH (basic) solution
3. High temperature
Effects:
4
Page
- Double helix separates because hydrogen bonds are disrupted
