17 final easy

Proteins

Links between genotype (DNA) and phenotype (traits)

Beadle & Tatum

Exposed bread molds to X-rays; led to 'one gene - one enzyme' hypothesis

One gene - one enzyme hypothesis

Each gene codes for a single enzyme or protein

Gene splicing

Genes code for products by joining exons and removing introns

Transcription

Synthesis of RNA using DNA as a template

Translation

Synthesis of a polypeptide using RNA as a template

RNA vs DNA

RNA: ribose, single-stranded, A/G/C/U; DNA: deoxyribose, double-stranded, A/G/C/T

RNA polymerase

Enzyme that pries DNA apart and synthesizes RNA

Promoter

DNA sequence where RNA polymerase binds to start transcription

Terminator

Sequence signaling the end of transcription (in bacteria)

Transcription unit

DNA segment being transcribed

Stages of Transcription

Initiation → Elongation → Termination

TATA box

Eukaryotic promoter crucial for initiation complex formation

Transcription factors

Chemicals that help RNA polymerase bind to DNA

Transcription initiation complex

RNA polymerase + transcription factors bound to promoter

Primary transcript

Initial RNA copy produced from DNA

RNA Editing (prokaryotes)

mRNA translated immediately after transcription

RNA Editing (eukaryotes)

Primary RNA transcript is processed (introns removed, exons joined)

Introns

Non-coding RNA sequences

Exons

Coding RNA sequences; expressed in proteins

RNA splicing

Introns removed, exons joined to make continuous mRNA

Spliceosome

Protein + snRNP complex that removes introns

5' cap

Modified guanine nucleotide added to 5' end of mRNA

Poly-A tail

50-250 adenines added to 3' end of mRNA

Functions of 5' cap & Poly-A tail

Protect mRNA, help export, help ribosome binding

Ribozymes

Catalytic RNA molecules that can splice RNA

Alternative RNA splicing

One gene can produce multiple proteins by using different exons

Domain

Discrete functional region of a protein

Exon shuffling

Mixing exons to create new proteins

Codon

3-nucleotide sequence coding for an amino acid

Start codon

AUG

Stop codons

UAA, UAG, UGA

Genetic code is redundant

Some amino acids have multiple codons

Genetic code is not ambiguous

One codon codes for only one amino acid

mRNA

RNA carrying genetic code of a protein

tRNA

RNA that carries amino acids to ribosome; has anticodon

Anticodon

tRNA sequence complementary to mRNA codon

Ribosome function

Matches tRNA anticodons with mRNA codons to synthesize proteins

Ribosome composition

rRNA + proteins

P site

Holds tRNA with growing polypeptide

A site

Holds tRNA with next amino acid

E site

Exit site for discharged tRNA

Translation stages

Initiation → Elongation → Termination

Initiation of translation requires

mRNA, initiator tRNA, ribosomal subunits

Steps of initiation

Small subunit binds mRNA + initiator tRNA → finds AUG → large subunit joins

Elongation steps

Codon recognition → peptide bond formation → translocation

Termination of translation

Stop codon reaches ribosome A site → translation ends

Polyribosome (polysome)

Multiple ribosomes translating one mRNA

Post-translation modifications

Proteins cleaved or combined; example: fibrin, collagen

Golgi apparatus

Modifies polypeptides after synthesis

Free ribosomes

Make cytosolic proteins

Bound ribosomes

Make ER/secreted proteins

Polypeptide synthesis begins

In cytosol

Polypeptide synthesis ends

In cytosol unless directed to ER

Signal peptide

Marks polypeptides for ER or secretion

Signal-recognition particle (SRP)

Binds signal peptide, brings ribosome to ER

Point mutations

Change in a single DNA base

Base-pair substitutions

Silent, missense, or nonsense mutations

Silent mutations

No effect on amino acid

Missense mutations

Wrong amino acid

Nonsense mutations

Changes amino acid to stop codon → nonfunctional protein

Mutagens

Physical or chemical agents causing mutations