Transcript From Gene to Protein Chapter 17. Defining a gene… “Defining a gene is challenging because… gene RNA •tRNA •rRNA protein •mRNA polypeptide 1 combine w/ other polypeptides The “Central Dogma”  How do we move information from DNA.

From
Gene
to Protein Chapter 17.
Defining a gene…
“Defining a gene is challenging because…
gene
RNA
•tRNA
•rRNA
protein
•mRNA
polypeptide 1
combine w/
other
polypeptides
The “Central Dogma”

How do we move information from
DNA to proteins?
transcription
DNA
replication
translation
RNA
protein
From nucleus to cytoplasm…

Where are the genes?


Where are proteins synthesized?


genes are on chromosomes in nucleus
proteins made in cytoplasm by ribosomes
How does the information get from nucleus to
cytoplasm?

messenger RNA
nucleus
RNA


ribose sugar
N-bases






uracil instead of thymine
A
C
G
single stranded
mRNA, rRNA, tRNA
transcription
DNA
RNA
Transcription

Transcribed DNA strand = template / coding strand


Untranscribed DNA strand = noncoding / nonsense strand
Enzyme

RNA polymerase
Carbon Numbers in nucleic acids
Enzymes involved in many steps

Enzymes are special proteins




Involved in making and breaking of
bonds (promote chemical reactions)
They interact with molecules and
increase the speed of chemical
reactions that would occur too slow
to sustain life.
They are not changed or used up in
the interactions.
Re-useable.
Transcription
RNA
Transcription begins with
INITIATION:

RNA polymerase enzymes




Recognizes specific promoter sequence on the DNA
Promoter located “before” the gene
Each gene has a promoter [analogy = address]
Role of promoter:
1. Locates where to start “copying” ;
2. Determines which DNA strand to “read” (the TEMPLATE /
CODING strand)
Transcription continues with
ELONGATION:
RNA polymerase
 moves down DNA strand
 adds RNA nucleotides
complementary to DNA
 adds to the new RNA
strand and it continues to
grow longer
Transcription ends with
TERMINATION:
RNA polymerase
 reaches a stop / termination sequence [end of
gene]
 Stops building
 Releases the RNA
DNA reforms helix
Explore these animations

University of Nebraska @ Lincoln
http://www-class.unl.edu/biochem/gp2/m_biology/animation/gene/gene_a2.html

St. Olaf College
http://www.stolaf.edu/people/giannini/flashanimat/molgenetics/transcription.swf

The University of Utah – Genetics Science Center
http://learn.genetics.utah.edu/units/basics/transcribe/
Translation
From gene to protein
transcription
DNA
a
a
a
polypeptide
a
mRNA
mRNA leaves
nucleus through
nuclear pores
nucleus
translation
a
a
a
a
a
a
a
ribosomea
cytoplasm
a
a
a
a
Translation
Codons

blocks of 3 mRNA
nucleotides
converted into
a sequence of
amino acids (a
polypeptide)
mRNA codes for polypeptides in
triplets
TACGCACATTTACGTACGCGG
DNA
mRNA
AUGCGUGUAAAUGCAUGCGCC
?
protein
Met Arg Val Asn Ala Cys Ala
The code

For ALL life!

strongest support for a
common origin for all life
Important Features?

Start codon



AUG
methionine [A.A.]
Stop codons

UGA, UAA, UAG
How are the codons matched to
amino acids?
DNA
mRNA
3'
5'
5'
3'
TACGCACATTTACGTACGCGG
AUGCGUGUAAAUGCAUGCGCC
codon
3'
tRNA
UAC
amino
acid
Met
5'
GCA
Arg
CAU
Val
anti-codon
aa
aa
aa
cytoplasm
transcription
translation
aa
aa
aa
aa
aa
protein
aa
aa
aa
nucleus
Translation Animations



University of Nebraska - Lincoln
Virtual Cell Animation
McGraw-Hill (more technical that you need to know, but an excellent
explanation)

You Tube – Translation video (very simplistic overview,
but well done)




ST. Olaf College
Biostudio.com
The U of Utah – Genetics Science Center
Wiley - animations
tRNA structure

“Clover leaf” structure


anticodon on “clover leaf” end
amino acid attached on 3' end
Charging tRNA

Enzyme bonds an amino
acid to tRNA
uses ATP – energy carrying
/ storage molecule in cells
 energy stored in
tRNA-amino acid bond



unstable
Releases amino acid at ribosome
Ribosomes (made of rRNA)

P site


A site


holds tRNA carrying growing polypeptide chain
holds tRNA carrying next amino acid to be added
to chain
E site (exit site)

empty tRNA
leaves ribosome
Building a polypeptide

Initiation


Elongation


Ribosome subunits clamp down on
mRNA and begin to read code.
Build polypeptide
Termination

Complete and release mRNA,
polypeptide, ribosome separates
Termination: release polypeptide

Release factor [stop codon]

“release protein” bonds to A site
Now what happens to the polypeptide?
Put it all
together…
Any Questions??