Quiz tiiiiime
• What 3 things make up a nucleotide?
• What molecule is used as a “battery” to allow the connection of
nucleotides to happen?
• What enzyme is in charge of unzipping and unwinding DNA in
replication?
• Why are telomeres important
• What does the “m” in mRNA stand for?
• What is a codon?
• What is the name of the box that acts as a promoter for
transcription?
• What is transcription?
• What type of molecule are DNA Polymerase, RNA polymerase, and
topoisomerase? How do you know?
Protein Synthesis
General Information
• Also called gene
expression
• DNA provides the
blueprints for the
building of
proteins
General Information
• Involves two
processes:
• Transcription- copying
DNA into mRNA
• Translation- translates
the code from nucleic
acid into amino acid
at the ribosome
Evolutionary Advantage of
Transcription and Translation
• DNA is protected inside the nucleus
• Using an RNA intermediate allows multiple
copies of a protein to be made at once
because many mRNA molecules can be made
from one gene, then translated repeatedly
Prokaryotes vs. Eukaryotes
Prokaryotes
• Only one compartment (no
nucleus)
• Transcription and
Translation occur
simultaneously
Prokaryotes vs. Eukaryotes
Eukaryotes
• Transcription occurs in the
nucleus
• The primary transcript is
then modified (RNA
processing) before leaving
the nucleus
• Translation occurs in the
cytoplasm at the ribosome
The Genetic Code
• Triplet Code- the flow if information from gene (DNA)
to protein is written in the DNA as non-overlapping,
three-nucleotide segments
• Template Strand:
• The mRNA is complimentary to the template strand
• The DNA is read in the 3’ to 5’
• The mRNA is synthesized and read from 5’ to 3’
The Genetic Code
• Codons- each three base sequence on the
mRNA strand
• Each codon codes for a specific amino acid
Redundant but not Ambiguous
• Redundant- multiple
codons can code for the
same amino acid
• Not Ambiguous- no
codon codes for more
than one amino acid
Special Codons
• AUG= start
• UAA, UAG, UGA= stop
Transcription
Initiation
• RNA polymerase binds to the promoter
• The promoter is a specific sequence that tells the
RNA polymerase where to bind and determines
what DNA strand will serve as the template
• In eukaryotes, specific proteins called
transcription factors assist the RNA polymerase in
binding and forming the transcription initiation
complex
Initiation
Elongation
• RNA polymerase adds
nucleotides to the 3’ end
of the growing RNA
molecule
• Complimentary base
pairing occurs
• The new RNA molecule
peals away from the DNA
template and the DNA
reforms
Termination
• In prokaryotes, the RNA polymerase detaches
after the termination signal is transcribed
• In eukaryotes, the RNA polymerase
transcribes the polyadenylation signal
sequence then the mRNA is cut off of the RNA
polymerase
RNA Processing
EUKARYOTIC
CELLS ONLY
Using pages 334 and 335…
• Describe RNA processing…
– What is it?
– What are two examples?
– What is the purpose of RNA processing?
• Describe Introns and Exons using Figure 17.10
Altering of the Ends of the mRNA
• 5’ cap- modified guanine molecule added on the 5’ end
• Poly-A-tail- 50-250 adenine nucleotides are added to
the 3’ end
•
•
•
•
Functions:
Facilitate export from the nucleus
Protect the mRNA from degradation by enzymes
Assist the ribosomes in attaching in the cytoplasm
RNA Processing
RNA Splicing
• Removal of large portions of the mRNA
• snRNPs (“snurps”) recognize and cut out areas of
the mRNA
• Introns- the portions of the mRNA that are
removed
• Exons- the portions of the mRNA that exit the
nucleus
Translation- Important Components
Transfer RNA, tRNA
• Translates nucleotides
into amino acids
• One end has an
anticodon,
complementary to the
mRNA codon
• The other end is bound to
an amino acid
• Excellent example of how
structure fits function
Ribosomes
• Contain three sites for holding tRNA:
• P site- holds the growing polypeptide
chaing
• A site- holds the tRNA that is carrying
the next amino acid in the chain
• E site- where the tRNA leaves the
ribosome
• Exit Tunnel= where the polypeptide
leaves the ribosome
Translation- The Process
Initiation
• Small ribosomal subunit binds the mRNA and
the initiator tRNA
• Subunit scans the mRNA until it reaches the
start codon, establishing the correct reading
frame as the tRNA hydrogen bonds to the
start codon
Initiation
• Translation initiation complex forms- the large
ribosomal subunit attaches with the
assistance of initiation factors and an
expenditure of energy
Elongation
Elongation
• The ribosome reads the mRNA in the 5’ to 3’ direction
• Anticodon of the incoming tRNA hydrogen bonds to
the mRNA codon in the A site
• The peptide bond forms between the amino acid on
the tRNA of the A site and the growing polypeptide
chain in the P site
• Translocation of the tRNA shifts the A site tRNA to the
P site and the P site tRNA to the E site so it can exit
Termination
• Release factor:
– Added when stop codon is reached
– Causes the addition of a water molecule to the
end of the polypeptide
• The polypeptide is released
Forming a Functional Protein
Protein Folding
• Folding occurs as the protein is being synthesized
• Folding is dependent on
– The properties of the peptide chain
– The physical and chemical properties of the environment
WHY MIGHT THIS BE A PROBLEM???
Chaperonins
• Proteins that assist in the proper folding of
other proteins by shielding them form the cell
environment
Post-Translational Modification
• Chemical modification by the attachment of
sugars, lipids, phosphate groups, or other
components
• Enzymes may remove one or more amino
acids from the N-terminus
• Single polypeptides may by cut into two or
more smaller pieces
Denaturation
• The changes in a protein’s native
conformation that renders it biologically
inactive
•
•
•
•
Factors that cause denaturation:
Change in the environment
Change in temperature
Change in pH
Changes in Environment
• If moved from an aqueous environment to a
nonpolar organic solvent, the protein will turn
inside out
• Chemicals can disrupt disulfide and hydrogen
bonds that stabilize secondary and tertiary
structure
Changes in Temperature
• Excessive heat can cause movement to
overpower sensitive hydrogen bonds
• Excessive cold will slow the protein down
substantially
Changes in pH
• All proteins have an optimal pH at which they
function
• Optimal pH is not necessarily 7