Download Les 6b RNA Transcription and Translation

Protein Synthesis
The Molecule of Life:
Transcription and Translation
Transcription and Translation
 Transcription begins the process of protein
synthesis
 Translation results in the end protein
molecule
 Several organelles in the cell are involved
Cell Organelles Involved in Protein
Synthesis (186)
Transcription:
Start of Protein Synthesis
 Where?
 Nucleus in Eukaryotes
 Cytoplasm in Prokaryotes
 What?
 Many cell organelles involved
 RNA Polymerase plus some minor proteins
 DNA code becomes encoded in mRNA
Transcription:
Start of Protein Synthesis
 When?
 When RNA is needed
 Why?
 RNA’s serve many important functions in
cells
 RNA encodes protein sequences
 How?
Transcription Defined
 Transcription: to transfer a code into
another code

ie. To rewrite one language into another
Where are we?
http://blog.coturnix.org/2008/05/01/lithium_circadian_clocks_and_b_2/
Transcription
 How?
 mRNA made 5’3’ directionality
 DNA unzips only at a specific gene
sequence for a specific protein
 Usually only one strand of DNA is read to
form a complementary copy of the mRNA
Transcription

Uses Base-pairing but U instead of T pairs
with A.



RNA nucleotides “float” into place with the aid
of RNA polymerase and complementary base
pairing occurs
There are nonsense codes at the end of the
gene that terminate mRNA synthesis.
mRNA breaks off and moves out of the nucleus
into the ribosomes of the cytoplasm
 Same idea as with DNA replication
 Transcription Animation
 Transcription & translation - fast
Transcription: Layout
 5’ end
RNA
 3’end
RNA
mRNA Enters Cytoplasm
http://www.dnatutorial.com/RNATranscriptionAnimation.shtml
Translation
 What?
 mRNA Protein molecule
 Where?
 Cytoplasm
 Ribosomes are main organelles
Translation
 When?

When proteins are need, after mRNA is made
 Why?

Proteins are vital for cells
 Enzymes, tissues, hormones, cell structure all
require proteins
The Genetic Code
Translation: Defined
 Translation: to interpret a code into
meaning.
 In biology: The process by which
messenger RNA directs the amino acid
sequence of a growing polypeptide
during protein synthesis.
Proteins: Structure and
Function
 Amino acids connect to form small
chains called peptides, which get larger
and form polypeptides.
 There are 20 amino acids useful to
humans
 We consume these in our diet, our body
makes a few
Proteins: Structure and
Function
 In anabolism, our body needs to
assemble these amino acids into
specific protein structures. A missing
amino acid means an entire protein
cannot be made—the RNA cannot “fill”
the hole left by its absence
 A.A. allow the protein molecule to form
its necessary structure
 Proteins have many structures/shapes
Peptide Bond Formation:
Dehydration Synthesis
From Amino Acid to Protein
Structure
The Big Question?
How do amino acids
assemble themselves
correctly?
Translation
 How?
 Ribosomal Subunits
 Small subunit
 Large subunit
 Codon on mRNA
 Triplet nucleotide code used
 Each triplet codes for a specific tRNA
attached to a specific amino acid
Translation
 How?
 mRNA, tRNA, & rRNA are all used
A couple definitions
 CODON:
 a triplet of nucleotides on the mRNA
 Triplet codes for a specific tRNA
complementarity
 The codon is the genetic code
 ANTICODON:
 A triplet of nucleotides on the bottom of the
tRNA
 Triplet anticodon complements the mRNA
codon
 tRNA brings a specific amino acid
The Genetic Code
Test for Understanding the
code
 A DNA sequence has the
following bases: T A C - A G
A-TTA-GGG-ATT
What amino acids does it
code for? (You'll need to use
the codon chart)
mRNA CODONS
AUG UCU AAU CCC UAA
Met–ser – asn – pro-stop
AUG usually is “START”
UAA is “STOP”
Amino acid sequence is actually
SER-ASN-PRO
tRNA each has one specific
amino acid and this is how
amino acids “know” the
sequence of attachment !
Recall tRNA
 Anticodon attaches to
codon
 Amino acid valine is
attached to this specific
tRNA
 Valine will always
attach to tRNA with the
same anticodon
 Amino acid binding site
is amino acid specific
Summary
 Translation
 DNA Rap
 protein synthesis
 Protein
Transport
http://www.biologycorner.com/bio4/notes/gene-expression.php
Why is this important?
 Genetic Engineering

Gene Splicing
 Mutations
 Cloning
 http://www.johnkyrk.com/DNAtranscription.html
 Castle Analogy
Mutations
 Point Mutations


Single base change
Base-pair substitution

Silent mutation
 No AA change

Missense
 AA change

Nonsense
 Stop codon change
 When do mutations
affect the next
generation?
A Mutations leads to Sickle Cell Anemia
 What kind of mutation?
Sickle Cell Anemia
Mutations
 Frameshift

Shift in reading
frame


Insertion


Changes everything
“downstream”
Adding a base(s)
Deletion

Losing base(s)
 Which is more
harmful – point or
frameshift?