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!