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
mRNA
Synthesis ofmRNA in thenucleus
DNA
NUCLEUSCYTOPLASM
1
Fig. 5-26-2
mRNA
Synthesis ofmRNA in thenucleus
DNA
NUCLEUS
mRNA
CYTOPLASM
Movement ofmRNA into cytoplasmvia nuclear pore
1
2
Fig. 5-26-3
mRNA
Synthesis ofmRNA in thenucleus
DNA
NUCLEUS
mRNA
CYTOPLASM
Movement ofmRNA into cytoplasmvia nuclear pore
Ribosome
AminoacidsPolypeptide
Synthesisof protein
1
2
3
Types of RNA Involved
• mRNA: Carries info from DNA to ribosome
• 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.
Types of RNA Involved
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. 17-8A eukaryotic promoterincludes a TATA box
3
1
2
3
Promoter
TATA box Start point
Template
TemplateDNA strand
535
Transcriptionfactors
Several transcription factors mustbind to the DNA before RNApolymerase II can do so.
5533
Additional transcription factors bind tothe DNA along with RNA polymerase II,forming the transcription initiation complex.
RNA polymerase IITranscription factors
55 53
3
RNA transcript
Transcription initiation complex
Elongation• Transcription progresses at a rate of 40
nucleotides per second in eukaryotes
• 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
Termination
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 splicing: removes introns (noncoding), joins exons (coding)
RNA Processing
Translation•m
RN
A m
essa
ge g
ets
trans
late
d in
to a
pro
tein
w/
help
of t
rans
fer
RN
A (t
RN
A)
Occurs at Ribosomes
• 2 ribosomal subunits (large and small) are made of proteins and ribosomal RNA (rRNA)
Ribosomes
• Either free floating in cytoplasm
•Or Attached to Rough Endoplasmic Reticulum
Ribosomes
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
• Amino acids join to make a peptide chain• Stop codon stops process, release of new peptide
chain.
Termination of Translation
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!