Central Dogma
Big Idea 3: Living systems store,
retrieve, transmit, and respond to
info essential to life processes.
Essential Knowledge
• 3A1: DNA, and in some cases RNA, is the
primary source of heritable information.
Central Dogma!
Protein Synthesis
• Genetic info flows from
nucleotide sequence in a
gene to amino acid sequence
in a protein
Fig. 5-26-1
DNA
1 Synthesis of
mRNA in the
nucleus
mRNA
NUCLEUS
CYTOPLASM
Fig. 5-26-2
DNA
1 Synthesis of
mRNA in the
nucleus
mRNA
NUCLEUS
CYTOPLASM
mRNA
2 Movement of
mRNA into cytoplasm
via nuclear pore
Fig. 5-26-3
DNA
1 Synthesis of
mRNA in the
nucleus
mRNA
NUCLEUS
CYTOPLASM
mRNA
2 Movement of
mRNA into cytoplasm
via nuclear pore
Ribosome
3 Synthesis
of protein
Polypeptide
Amino
acids
Types of RNA Involved
• mRNA: Carries info from DNA to
ribosome
Types of RNA Involved
• tRNA: Bind specific amino acids and allow info
in the mRNA to be translated into a linear
peptide sequence.
Types of RNA Involved
• rRNA: functional building blocks of
ribosomes (site of translation)
Types of RNA Involved
• RNAi: RNA
interference molecules
that inhibit gene
expression; sometimes
destroy mRNA.
• 2 molecules involved:
microRNA and siRNA
(small interfering RNA)
that regulate gene
expression.
Transcription Occurs
Here!
Translation Occurs
Here!
Transcription
• DNA  mRNA,
made by RNA
polymerase II
• RNA polymerase
binds on promoter
(nucleotide), reads
DNA from 3’ to 5’
• 3 stages:
Initiation,Elongation,
Termination
RULE!
• A on DNA complements U on RNA
• RNA has no T base!
Initiation
• Promoters: start RNA synthesis, TATA box
is one in eukaryotes
• Transcription factors: help binding of RNA
polymerase
• Completed assembly called a transcription
initiation complex
Fig. 17-8
1
Promoter
A eukaryotic promoter
includes a TATA box
Template
5
3
TATA box
Start point
2
Transcription
factors
3
5
Template
DNA strand
Several transcription factors must
bind to the DNA before RNA
polymerase II can do so.
5
3
3
5
3
Additional transcription factors bind to
the DNA along with RNA polymerase II,
forming the transcription initiation complex.
RNA polymerase II
Transcription factors
5
3
3
5
5
RNA transcript
Transcription initiation complex
Elongation
• Transcription progresses at a rate of 40
nucleotides per second in eukaryotes
Termination
• In bacteria: polymerase stops transcription at end
of terminator (nucleotide sequence)
• In eukaryotes: polymerase continues transcription
after pre-mRNA is cut  polymerase eventually
falls off DNA
RNA Processing
• Enzymes modify mRNA
• Ex: Addition of poly-A tail on 3’ end and a GTP 5’
Cap
• Helps export mRNA and protect from degrading
hydrolytic enzymes
RNA Processing
• RNA splicing: removes introns
(noncoding), joins exons (coding)
Translation
Occurs at Ribosomes
• 2 ribosomal subunits (large and small) are made of
proteins and ribosomal RNA (rRNA)
Ribosomes
• Either free floating in cytoplasm
Ribosomes
•Or Attached to Rough Endoplasmic Reticulum
P Site: holds tRNA that carries growing
polypeptide chain
A Site: holds next tRNA that will
add a. acid to chain
E Site: holds exit tRNA that
doesn’t have an a. acid
Ribosomes
Initiation of Translation
• mRNA interacts w/ rRNA of ribosome at start codon
AUG
• mRNA is read in triplets called codons, which encodes a
specific amino acid.
• tRNA carries the amino acid to the mRNA and ribosome
Termination of Translation
• Amino acids join to make a peptide chain
• Stop codon stops process, release of new peptide
chain.
Amino Acid Sequences
mRNA and Transcription
Big green thing = RNA polymerase
Protein Synthesis Videos
• NOVA: DNA
Secret of
Life
Prokaryotic Protein Synthesis
Phenotypes are determined through
protein synthesis!