Ch. 11.4 & 11.5: Transcription & Translation

Objectives: • Explain one-gene-one polypeptide

hypothesis.

• Describe the process of transcription.

• Explain how RNA is edited.

• Describe how RNA is translated into a protein.

• Describe how amino acids are coded.

• Summarize protein synthesis.

Vocab.: Transcription, RNA (ribonucleic acid), mRNA, RNA polymerase, intron, extron,

RNA splicing

Translation, tRNA, codon, anticodon, Codon, rRNA

One Gene, One Polypeptide

Genotype: sequence of nucleotides bases in DNA.

Phenotype: Organism traits; based on proteins & protein fxns

Beadle & Tatum: Research leads to “One gene, one enzyme”

Beadle & Tatum Experiment: 9:57 min http://www.youtube.com/watch?v=vP_h08cT5jw

•Expose bread mold to X-rays (Mutation = Damaged DNA).

•Essential enzyme/amino acid cannot be made from damaged DNA.

•Mutated mold won’t grow on “minimal” medium that lacks enzyme/amino acid it can’t make.

“one enzyme” - not accurate. 1 gene = 1 poly-peptide (part of 1 enzyme/protein)

RNA carries DNA instructions to Ribos.

Ribosomes make PROTEINS.RNA: Ribonucleic AcidSingle strand nucleotide1. 5-C Sugar: Ribose2. Phosphate3. Nitrogen base

(A, U, G, C)U = Uracil; Replaces TA binds to U; G binds to C

Transcription: DNA --> mRNA • DNA cannot leave

nucleus.• DNA nucleotide sequence

is converted into mRNA (messenger RNA).

• mRNA leaves nucleus --> directs protein synthesis @ ribo. in cytoplasm.

http://www.youtube.com/watch?v=983lhh20rGY&feature=related

http://www.youtube.com/watch?v=41_Ne5mS2ls

Transcription: RNA Polymerase• Enzyme that links

RNA nucleotides together (like DNA polymerase)

• Transcribes specific segments of DNA.

RNA SPLICING: Editing mRNA

Splicing: In eukaryotes mRNA is modified before it leaves nucleus.

1. INTRONS removed/spliced

• non-coding sequences (junk)

• Do not code for amino acids

2. EXONS:

• Coding sequences

• Translate into amino acids (expressed)

Modifying mRNA

Translation: mRNA --> proteins• Based on CODON “language”

• 3-bases translate into a CODE for specific amino acids.

• Amino acids build polypeptides.

Nucleic acids --> Proteins

TRANSLATIONEach codon codes for 1 amino acid.

Start codons:

AUG (start translating)

Stop codons:

UAA, UAG, UGA

Same codes for almost ALL organisms!

Translation

Required• ATP• mRNA• Ribosomes• tRNA

tRNA: Transfer RNA• Translates codon of mRNA into amino acids.• “Fetches” correct amino acid• Attatches to correct codon.• Has “anti-codon” complement to attatch to codon.

Translation: rRNA (Ribosome)

rRNA: ribosome (organelle)

• 2 subunits snap together.

• mRNA and tRNA join each other in RIBOSOME.

2 tRNA binding sites where translation happens:

P site: Growing polypeptide chain.

A site: new amino acid binds

Translation: Elongation

Polypeptide chain grows.• Translation begins (AUG) codon• Amino acids are added by tRNA

(based on mRNA codons).• Translation ends (UAA, UAG, UGA);

stop codon.• Polypeptide released (Goes to E.R. and

Golgi for modification)

Translation Summary