ch 13 Gene expression

Transcription

occurs in nucleus,

synthesis of RNA,

information for the process: a segment of one DNA strand,

product: one RNA molecule (e.g. mRNA, tRNA, rRNA),

Major Enzyme or structure involved in the process: RNA polymerase

type of base paring required: RNA with DNA- RNA bases pair with the DNA bases as an RNA molecule is synthesized

Translation

occurs in the cytoplasm

synthesis of protein

information for the process- mRNA,

product- one protein molecule,

major enzymes or structure involved in the process- ribosomes (also requires tRNA),

type of base paring required- mRNA with tRNA- a codon in mRNA forms base pairs with anticodon in tRNA

What is transcription?

transcription if a gene produces an mRNA with a nucleotide sequence complementary to one of the DNA strands

What is translation?

translation of the mRNA produces a protein with an amino acid sequence determined by the nucleotide sequence of the mRNA

Steps in translation

1. unwind DNA and one strand serves as a template to make RNA ,

2. complimentary base paring occurs, attaching RNA nucleotides => mRNA rolls off (e.g. TCAGATCT—AGUCUAGA)

3. mRNA is processed = edited,

4. Completed mRNA leaves nucleus for translation

Players involved for translation

1. mRNA- “messenger” RNA, carries a transcript gene,

2. Amino acid= building blocks (monomer) of protein,

3. Ribosome= make protein, attach amino acids together,

4. tRNA= Transfer RNA, brings amino acids to the ribosomes,

5. rRNA= ribosomal RNA, main component of ribosomes.

Steps in translation (mRNA-- protein)

1. initiation- “players arrive”- ribosomes attaches to the mRNA (at START codon) and the tRNA brings the 1st amino acid.

2. Elongation- “play game”- next tRNA brings an amino acid, and the ribosomes attaches amino acid, etc. building a protein,

3. termination- “game’s over”- ribosomes reaches a STOP codon, everything is released—> protein is made

Consequences of mutation

deletion and insertion mutation both result in a frameshift

• (e.g. THE CAT ATE – THE eCAT ATE --- THE eCA Tat E – insertion),

  • a different sequence of amino acids = nonfunctional proteins

nucleotide substitution- substitution-> changes mRNA codon-> different amino acid -

• e.g. sickle cell anemia,

silent mutation- substitution -> changes codon-> same animo acid

• e.g. normal, functional protein.

Nonsense substitution -> STOP codon

• e.g. nonfunctional, incomplete protein

DNA vs RNA

DNA

• 2 strands

• nucleotide

  • phosphate

  • nitrogenous base

    • A,T, C, G

RNA

• 1 strand

• nucleotide

  • phosphate'

  • ribose

    • A, U, C, G *no thymmine, uracil instead