central dogma - university of arizonaeebweb.arizona.edu/courses/ecol223/protein synthesis...

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Cytoplasm

Nucleus

DNA

DNA is the genetic material within the nucleus.

Central Dogma

RNA

Protein

Replication

The process of replication creates new copies of DNA.

TranscriptionThe process of transcription creates an RNA using DNA information.

TranslationThe process of translation creates a protein using RNA information.


Transcription• DNA is used as a template for creation

of RNA using

• the enzyme RNA polymerase.DNA

5’

3’

5’

3’

G T C A T T C G G

C A G T A A G C C


Transcription• RNA polymerase reads the nucleotides

on the

• template strand from 3’ to 5’ and creates an RNA

• Molecule in a 5’ to 3’ direction that looks like the coding strand.G T C A T T C G G

C A G T A A G C C


Transcription• The new RNA molecule is formed by incorporating

• nucleotides that are complementary to the template strand.

DNA coding strand

DNA template strand

DNA

5’

3’

5’

3’

G T C A T T C G G

C A G T A A G C C

G

RNA

5’

GG U C A U U C

3’


Two types of nucleic acids•RNA

•Usually single-stranded

•Has uracil as a base

•Ribose as the sugar

•Carries protein-encoding information

•Can be catalytic

•DNA

•Usually double-stranded

•Has thymine as a base

•Deoxyribose as the sugar

•Carries RNA-encoding information

•Not catalytic


Two types of nucleic acids

# of strands

kind of sugar

bases used


rRNA is part of ribosome, used to translate mRNA into protein


tRNA is a connection between anticodon and amino acid


TATA binding protein

Initiation of transcription

DNA GG TATA CCC

Transcription begins

Promoter Gene sequenceto be transcribed

TATA box

Transcription begins at the 3’ end of the gene in aregion called the promoter.

When a complete transcription complex is formed RNA polymerase binds and transcription begins.

The promoter recruits TATA protein, a DNA binding protein, which in turn recruits other proteins.

Transcription factor


• Noncodingsegments called introns are spliced out

• A cap and a tail are added to the ends to protect against degradation in the cytoplasm

10.10 Eukaryotic RNA is processed before leaving the nucleus

Figure 10.10

DNA

RNAtranscriptwith capand tail

mRNA

Exon Intron IntronExon Exon

TranscriptionAddition of cap and tail

Introns removed

Exons spliced together

Coding sequenceNUCLEUS

CYTOPLASM

Tail

Cap


Fig. 10.20


• Virtually all organisms share the same genetic code

• All organisms use the same 20 aa

• Each codon specifies a particular aa

10.8 The genetic code is the Rosetta stone of life

Figure 10.8A


• Three codons do not code from an aa

• Rather they are found at the end of the coding sequence

• Tell a ribosome to stop translation and release the protein

10.8 The genetic code is the Rosetta stone of life

Figure 10.8A


• Tryptophan and Methionine have only 1 codon each

• All the rest have more than one

• AUG has a dual function

• 3 stop codons that code for termination of protein synthesis

• Redundancy in the code but no ambiguity

Figure 10.8A


Translation• The process of reading the RNA sequence of an

mRNA and creating the amino acid sequence of a protein is called translation.

Transcription

Codon Codon Codon

Translation

DNA

T T C A G T C A G

DNAtemplatestrand

mRNA

A A G U C A G U C MessengerRNA

Protein Lysine Serine ValinePolypeptide(amino acidsequence)


• In the cytoplasm, a ribosome attaches to the mRNA and translates its message into a polypeptide

• The process is aided by transfer RNAs

10.11 Transfer RNA molecules serve as interpreters during translation

Figure 10.11A

Hydrogen bond

Amino acid attachment site

RNA polynucleotide chain

Anticodon


A codon of three nucleotides determines choice of amino acid


Translation is composed of three steps

• Initiation translation begins at start codon(AUG=methionine)

Elongation the ribosome uses the tRNAanticodon to match codons to amino acids and adds those amino acids to the growing peptide chain

Termination translation ends at the stop codonUAA, UAG or UGA


• mRNA, a specific tRNA, and the ribosome subunits assemble during initiation

Figure 10.13B

1

Initiator tRNA

mRNA binding site

Startcodon Small ribosomal

subunit

2

P site

LargeRibosomalsubunit

A site


Translation initiation

Leadersequence

mRNA5’ 3’

mRNA

A U GU U C G U C G G A C G AU G U A A G A

Small ribosomal subunit

Assembling to begin translation

Met

U A C

Initiator tRNA


Translation Elongation

CU A

Met

mRNA5’ 3’

Amino acidLarge ribosomal subunit

C C U

tRNA

Ribosome

Gly

U U U CG G G G GGA A A A A

P A



CU A

Met

mRNA5’ 3’

C C U

Gly


AAC

Cys

P A



mRNA5’ 3’

CC

U

MetGly

CU U

Lys

Lengtheningpolypeptide(amino acid chain)

A AC

Cys


P A



mRNA5’

U U U CG G G G GGA A A A A U A A

Stop codon

C UG

Arg

CU U

Lys

MetGly

Cys

Releasefactor

A

AC

P

A


Translation Termination

mRNA5’

CU U

Met Gly CysLys

Stop codonRibosome reaches stop codon

C UG

Arg

U U U CG G G G GGA A A A A U A A

ReleasefactorP

A


Translation Termination

UU U C

G G G G GGA

A A A A U A A

C UG

Met GlyCys

LysArg

ReleasefactorP

Once stop codon is reached, elements disassemble.

A


Levels of protein structurePrimary structure sequence of amino

acidsSecondary structure shapes formed with

regions of the protein (helices, coil, sheets)

Tertiary structure shape of entire folded protein due to interactions between particular peptides

Quaternary structure structures formed by interaction of several proteins togethere.g. Functional hemoglobin istwo alpha-hemoglobin proteins andtwo beta-hemoglobin proteins


10_14d.jpg


Levels of protein structure


Misfolding of protein impairs function

•Misfolded prion protein disrupts functions of other normally folded prion proteins. •Aberrant conformation can passed on propagating likean “infectious” agent.


10_18.jpg

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