MOLECULAR GENETICS

Polypeptide Synthesis Protein Structure

Sequence of amino acids

Nucleotide ConnectionSequence of nucleotides in the gene

determines the sequence of amino acids in the protein.

Fig. 24.10

Polypeptide SynthesisSynthesis Components

RNA (Ribonucleic acid) Structure

Phosphate Group Ribose Sugar Nucleotide Bases Types A, G, C, Uracil

DEOXYRIBONUCLEIC ACID (DNA)

RIBONUCLEIC ACID (RNA)

RNA (Ribonucleic acid)

TypesRibosomal (rRNA)

Structure RNA that is wrapped with proteins to

form ribosomes.Purpose

Synthesis of primary protein structure

RNA (Ribonucleic acid)

TypesMessenger (mRNA)

Structure Single strand of RNA nucleotides complementary to a gene on the DNA coding strand.Purpose

Carry protein-building instructions to ribosome.

RNA (Ribonucleic acid)

TypesTransfer (tRNA)

Structure 3-looped structure of about 80 nucleotides. Purpose

Bind and deliver specific amino acids to ribosomes.

POLYPEPTIDE SYNTHESIS

Mechanism Transcription

Definition Synthesis of a single-stranded mRNA using a DNA template and

conservative replication.

Fig. 24.10

Fig. 25.6

Transcription

StepsI. DNA Strand Separation DNA helicase unwinds the DNA double

helix at the promoter site creating a “Replication Fork”.

Fig. 25.6

Fig. 25.5

DNA HELICASE

TranscriptionSteps

II. Complementary Base Pairing RNA nucleotides pair with complementary nucleotides on one DNA strand (coding strand).

COMPLEMENTARY BASE PAIRING

CODING STRAND

NONCODING STRAND

Transcription Steps

III. Nucleotide Joining RNA polymerase joins the phosphodiester backbone of two adjacent RNA nucleotides to form

the polymer.

RNA POLYMERASE

3’ 5’

Transcription Steps IV. DNA Helix Reformation

DNA rewinds as transcription is completed (conservative replication).

Conservative Replication

TranscriptionSteps

V. RNA Modification Primary mRNA is chemically

modified to remove introns using a spliceosome resulting in continuous exons in the mature mRNA.

Fig. 25.4a

Transcription Steps

VI. Messenger RNA Transport RNA passes out of the nucleus

through nuclear pores to cytoplasm.

mRNA TRANSPORT

EXERCISE 5PG. 55

EXERCISE 5PG. 55