Download From Genes to Proteins What do genes code for?

Protein Synthesis Notes
1/11/2017
From Genes
to Proteins
What do genes code for?
PROTEINS
 Regulatory functions
 Other stuff?

DNA
proteins
EVERY trait of the organism!
Skiles, AP BIO
1
Protein Synthesis Notes
1/11/2017
The “Central Dogma”
The flow of genetic information in a cell
DNA
RNA
replication
protein
trait
Retroviruses transcribe RNA into DNA through the use of an enzyme
called reverse transcriptase: RNA → DNA → RNA → protein
Some very primitive viruses use only RNA → proteins
Prions are proteins directly replicating themselves by making
conforma onal changes in other proteins, Protein → Protein (SCARY)
BUT retroviruses, primitive viruses, and prions are technically not
considered "alive”
Do any organisms violate the
central dogma?
a
Protein Synthesis: From gene to protein
a
a
a
trait
a
nucleus
a
a
DNA
transcription
mRNA
translation
a
a
protein
a
a
a
cytoplasm
Skiles, AP BIO
2
Protein Synthesis Notes
1/11/2017
RNA
• Monomers = nucleotides
• Ribose sugar
• Nitrogen Bases
• uracil instead of
thymine
• U bonds with A
• C bonds with G
• Single stranded
• Location:
• Nucleus or cytoplasm
RNA
Types of RNA
• Ribosomal RNA (rRNA)
• Major component of ribosomes
• Transfer RNA (tRNA)
• Folded upon itself
• Carries the amino acids to the mRNA at ribosome
• Messenger RNA (mRNA)
• Sequence of nucleotides that determines the sequence of amino
acids
• Made in the nucleus from copying a DNA section: transcription
• Small-nuclear RNA (snRNA or “snurps”)
• Forms the “spliceosomes” which are used to cut out introns
from pre-mRNA
• Small-interfering RNA (siRNA)
• targets specific mRNA and prohibits it from being expressed
Skiles, AP BIO
3
Protein Synthesis Notes
1/11/2017
Transcription: DNA info copied to mRNA
• Location: Nucleus
• RNA polymerase:
(gene)
• AND
a DNA section
direction
in 5’to 3’
• mRNA Leaves the
nucleus through the
nuclear pores to find a
ribosome
http://content.dnalc.org/content/c16/16905/16905_
transcription_advanced.jpg
Coding strand = this side of DNA actually has the nucleotide
sequence that ‘spells out’ the protein needed, a.k.a. the “sense
strand”
Template strand (noncoding) = the opposite side of the DNA,
used to build the mRNA, a.k.a. the “anti-sense strand”
WHY USE THE OPPOSITE SIDE???
Skiles, AP BIO
4
Protein Synthesis Notes
1/11/2017
How is Transcription Started?
Transcription Factors
• Cell signal to transcribe
• Bind to promoter region
• The “TATA Box”
• Other TF’s bind
• RNA polymerase can
now bind
• Turns gene on OR off
Modifying the Transcript
Splice animation
Exons =
• expressed / coding DNA
Introns = non-coded section
• in-between sequence
Spliceosomes cut out introns with snRNAs
intron = noncoding (inbetween) sequence
eukaryotic DNA
exon = coding (expressed) sequence
Skiles, AP BIO
5
Protein Synthesis Notes
1/11/2017
Alternative Splicing
• Not all the exons may make it to the final product
• Intron presence can determine which exons stay or go
• Increases efficiency and flexibility in making proteins
Final mRNA processing for Eukaryotes
• Need to
cytoplasm
mRNA!)
mRNA moving to
(enzymes in cytoplasm will attack
• add 5 GTP cap
• add poly-A tail
3'
A
mRNA
5'
Skiles, AP BIO
G
P
P
P
6
Protein Synthesis Notes
1/11/2017
Summing Up Transcription:
Understanding the Genetic Code
DNA code is almost universal amongst all
organisms (evolutionary heritage)
• Each CODON of mRNA is 3 nucleotides (EX: CCG, AUG)
• Each 3 nucleotides “spells out” a specific amino
acid
• 64 different codon combinations possible
• Only 20 amino acids exist in the human body
• Some codons code for the same amino acids (degenerate or
redundancy)
mRNA sequence = amino acid sequence of
protein
• (ex: Protein: AUG-CCG is NOT the same as CCG-AUG!)
Skiles, AP BIO
7
Protein Synthesis Notes
1/11/2017
CODON CHART
• You don’t need to
memorize the
codons*, we have a
chart for that

Start codon



AUG
methionine
Stop codons

UGA, UAA, UAG
*except for start and
stop- know those
ones..
mRNA codes for proteins in triplets
DNA
TACGCACATTTACGTACGCGG
codon
mRNA
AUGCGUGUAAAUGCAUGCGCC
?
protein
Skiles, AP BIO
MetArgValAsnAlaCysAla
8
Protein Synthesis Notes
1/11/2017
TRANSLATION:
Reading the code from
mRNA to build an amino
acid sequence (protein)
Translation Needs
RIBOSOMES
• Made of rRNA and
proteins
• Function: Facilitates
bonding of correct
tRNA anticodon to
mRNA codon to
build the protein
Skiles, AP BIO
E P A
9
Protein Synthesis Notes
1/11/2017
Translation: Transfer RNA
• Contains anticodon
• tRNA anticodons bind
to mRNA codons
• Some tRNA may bind with more
than one codon (Supports
redundancy)
• “Wobble” hypothesis is that
anticodon with U in third position
can bind to A or G
Translation purpose: mRNA to Protein
• Location: cytoplasm
1. Initiation - start codon found (AUG)
2. Elongation – amino acids are joined
3. Termination – a STOP codon is reached
Skiles, AP BIO
10
Protein Synthesis Notes
1/11/2017
RNA polymerase
DNA
Can you tell
the story?
amino
acids
exon
pre-mRNA
intron
tRNA
5' GTP cap
mature mRNA
poly-A tail
large ribosomal subunit
polypeptide
5'
small ribosomal subunit
3'
tRNA
E P A
ribosome
Protein Synthesis in Prokaryotes
• Transcription & translation are simultaneous
in bacteria
• no mRNA
editing
• ribosomes
read mRNA
as it is being
transcribed
Skiles, AP BIO
11
Protein Synthesis Notes
1/11/2017
Prokaryote vs. Eukaryote
Protein Synthesis Differences
• Prokaryotes
• DNA in cytoplasm
• circular
chromosome
• naked DNA
• no introns
• No splicing
• Promoter &
terminator
sequence
• Smaller ribosomes
Skiles, AP BIO
• Eukaryotes
• DNA in nucleus
• linear chromosomes
• DNA wound on
histone proteins
• introns and exons
• “TATA” box
promoter
• Transcription factors
present
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