STUFF TO KNOW BIO FINAL - WEST

Chargaff's rule

A = T, C = G, purines = pyrimidines (A + G = T + C)

Base percentage rules

%A = %T, %C = %G, total = 100%

Complementary base pairing

A pairs with T, C pairs with G

Antiparallel DNA strands

One strand runs 5'→3', other runs 3'→5'

5' end

Phosphate group

3' end

Hydroxyl (-OH)

DNA synthesis direction

Always 5'→3'

High GC content effect

Increases DNA melting temperature

GC bonds

3 hydrogen bonds (stronger)

AT bonds

2 hydrogen bonds (weaker)

Helicase

Unwinds DNA strands

SSB proteins

Stabilize single-stranded DNA

Primase

Makes RNA primers

DNA polymerase III

Adds nucleotides during replication

DNA polymerase I

Replaces RNA primers with DNA

Sliding clamp

Holds DNA polymerase in place

Leading strand

Continuous DNA synthesis

Lagging strand

Discontinuous synthesis in Okazaki fragments

Okazaki fragments

Short DNA segments on lagging strand

Why Okazaki fragments form

DNA polymerase only works 5'→3' on antiparallel strands

Telomerase

Enzyme that extends chromosome ends

Mismatch repair

Fixes replication errors

Excision repair

Removes damaged DNA bases

PCR formula

copies = initial DNA × 2ⁿ

Denaturation (PCR)

DNA strands separate (~95°C)

Annealing (PCR)

Primers bind (~50-65°C)

Extension (PCR)

DNA is synthesized (~72°C)

RNA polymerase

Makes RNA from DNA template

RNA synthesis direction

5'→3'

Coding strand

DNA strand matching RNA (T replaced with U)

Transcription initiation

RNA polymerase binds promoter

Transcription elongation

RNA strand is built

Transcription termination

Stop of RNA synthesis

Rho-independent termination

Hairpin loop stops transcription

Rho-dependent termination

Rho protein detaches RNA

Operon

Cluster of genes controlled together (prokaryotes)

Polycistronic mRNA

One mRNA codes for multiple proteins

5' cap

Protects eukaryotic mRNA

Poly-A tail

Stabilizes eukaryotic mRNA

Alternative splicing

One gene produces multiple proteins

Ribosome A site

Incoming tRNA binds

Ribosome P site

Growing peptide chain

Ribosome E site

tRNA exits

Codon

mRNA triplet coding for amino acid

Anticodon

tRNA sequence matching codon

Wobble

Flexibility at 3rd codon base

Aminoacyl-tRNA synthetase

Loads amino acids onto tRNA

Peptidyl transferase

Forms peptide bonds

Release factor

Stops translation at stop codon

Protein direction

N-terminus → C-terminus

Origin of replication

Start of DNA replication

Promoter

Start site of transcription

Start codon

AUG

Point mutation

Single base substitution

Transition mutation

Purine↔purine or pyrimidine↔pyrimidine

Transversion mutation

Purine↔pyrimidine

Insertion

Extra base added

Deletion

Base removed

Frameshift mutation

Indel not divisible by 3

Silent mutation

No amino acid change

Missense mutation

Amino acid changes

Nonsense mutation

Early stop codon

Chromosome deletion

Loss of DNA segment

Chromosome duplication

Segment repeated

Chromosome inversion

Segment flips orientation

Chromosome translocation

Segment moves to another chromosome

Spontaneous mutation

DNA replication errors or tautomer shifts

Induced mutation

Caused by UV, chemicals, radiation

Somatic mutation

Not inherited

Germline mutation

Inherited mutation

Sigma factor

Directs RNA polymerase to promoter

Operon parts

Promoter, operator, structural genes

lac operon

ON with lactose, OFF without

trp operon

ON without tryptophan, OFF with tryptophan

Negative regulation

Repressor blocks transcription

Positive regulation

Activator increases transcription

DNA methylation

Turns genes OFF

Histone acetylation

Turns genes ON

X-inactivation

One X chromosome silenced via Xist

miRNA

Blocks translation or degrades mRNA

siRNA

Degrades target mRNA

Deletion

Chromosome segment lost

Duplication

Segment repeated

Inversion

Segment flips orientation

Translocation

Segment moves to another chromosome

Spontaneous mutations

DNA replication errors or tautomer shifts

Induced mutations

Caused by UV light, chemicals, radiation

Somatic mutation

Mutation in body cells, not inherited

Germ-line mutation

Mutation in gametes, inherited

Mutation before replication

Both daughter strands inherit mutation

Mutation during replication

Only one daughter cell inherits mutation

DNA → RNA → Protein → Trait

Flow of genetic information

Amino acid change effect

Can change protein shape or function

Active site mutation

Can cause loss of enzyme function

Stop codon mutation

Creates truncated protein

Silent mutation

No change in amino acid sequence

Sigma factor

Directs RNA polymerase to promoters

-35 region

Sigma binding site

-10 region (Pribnow box)

DNA unwinding site

Operon

Cluster of genes controlled together in prokaryotes