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MOLECULAR GENETICS
Polypeptide Synthesis
Protein Structure
Sequence of amino acids
Nucleotide Connection
Sequence of nucleotides in the gene
determines the sequence of amino acids
in the protein.
Fig. 24.10
Polypeptide Synthesis
Synthesis 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)
Types
Ribosomal (rRNA)
Structure
RNA that is wrapped with proteins to
form ribosomes.
Purpose
Synthesis of primary protein structure
RNA (Ribonucleic acid)
Types
Messenger (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)
Types
Transfer (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
Steps
I. 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
Transcription
Steps
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
Transcription
Steps
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 5
PG. 55
EXERCISE 5
PG. 55