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