Gene- a series of nucleotides found on a strand of DNA that codes for a particular proteinProtein Synthesis- when the info stored on a gene is “read” and then used to make a protein3 Parts to Protein Synthesis:

1. Transcription- creating RNA from DNA (occurs in the nucleus)2. Processing- When RNA is trimmed of its non-protein-coding nucleotides, made small enough that it can exit the nucleus3. Translation- The RNA assembles a specific sequence of amino acids to make the desired protein (occurs on the ribosome)

The Big Picture!!• There are 3 macromolecules

involved in Protein Synthesis • DNA makes RNA•RNA codes for proteins•Proteins carry out ALL of the cell’s important functions and activities

Recall: There are Two Types of Nucleic Acids

DNA – Deoxyribonucleic Acid

RNA – Ribonucleic Acid Similarities:

1. Nucleic acids2. Store genetic material3. Made up of strands of

nitrogen bases4. Follow some type of

Base Pairing Rules

Differences Between RNA/DNA

DNA:Double-strandedCytosine-GuanineAdenine- Thymine5-carbon sugar =

deoxyriboseNever leaves

Nucleus

RNA:Single-StrandedCytosine –GuanineAdenine- Uracil5-carbon sugar =

riboseCan leave nucleus

RNA types Three major types: (to be discussed

further)1. Messenger (mRNA)2. Ribosomal (rRNA)3. Transfer (tRNA)

mRNATemporary copy of a gene that

encodes for a protein; Provides the pattern that

determines the order and types of amino acids making that protein.

Very unstable, cell WILL try to break it down unless it is processed

Contain codons (3-base sequence) Precursor mRNA – exists in nucleusMature mRNA – genes to be copied

by ribosome (has been processed) exists in cytoplasm

rRNAMakes up 80% of RNA in

cellsUsed to make portions of

ribosomes in cells in combination with proteins.

Can be free floatingOr attached to Endoplasmic

reticulum (RER)

tRNAFree floating in cellEnzyme attaches ONE

tRNA to ONE amino acid(charged tRNA)

tRNA ‘carries’ the amino acid to ribosome to add to the growing polypeptide (protein) chain

Contains an anti-codon sequence (3-bases as bottom of tRNA), which is complementary to each codon

•  The nucleotides serve as the four “letters” of the DNA “alphabet” (A,C,G, & T)• 3 nucleotides make a Codon (ex. AAG)• Codons code for an Amino Acid (AAG codes for

lysine)• Amino Acids are the building blocks for proteins• Since there are 4 nucleotides, when three are

grouped together, there are 64 possible triplet combinations (43 = 64)• However, there are only 20 amino acids so some

amino acids have more than one codon (ex. GGA, GGC, and GGG all code for glycine)

The Genetic Code-

Summary:DNA = permanent copy (like your hard

drive)RNA = Temporary copy (similar to floppy

copy)Leads up to two of the most important

processes: Transcription and Translation

animation

Part 1: TranscriptionThe building of mRNA, tRNA, and rRNA (takes

place in the NUCLEUS)STEPS:  Initiation: RNA polymerase binds to the gene’s promoter

on the template strand of DNA(a specific sequence of the DNA that acts as a “start signal” for transcription)

RNA polymerase unwinds and separates the two strands of the DNA.

Elongation: RNA polymerase adds and then links complementary RNA nucleotides as it “reads” the gene”.

Termination: A “stop” signal on the DNA tells the RNA polymerase to detach from the DNA and release the RNA molecule.

Tutorial/Quiz

Part 2: RNA ProcessingBefore leaving the nucleus……..1.A cap (methyl-guanine or mG) is added by enzymes to the starting end of the mRNA molecule2.A poly-A tail is added to the end of the mRNA3.The molecule is spliced. Introns are removed (non-coding nucleotides) and exons remain.

RNA Processing Animation

Part 3: TranslationTutorialThe assembly of a protein (occurs on the ribosome in the cytoplasm)1.mRNA leaves the nucleus through the nuclear pore and forms a functional ribosome with two ribosomal subunits, and a tRNA2.Initiation: The mRNA “start” codon AUG is oriented in a region of the ribosome called the P site where the tRNA molecule carrying methionine can bind to the start codon.

Translation- cont. (another animation)3. The codon in the area of the ribosome

called the A site is ready to receive the next tRNA.

4. Elongation: Both the A site and the P site are holding tRNA molecules- each carrying a specific amino acid. A peptide bond forms between the adjacent amino acids

5. The tRNA in the P site detaches and leaves its amino acid behind

6. The tRNA in the A site moves to the P site. The tRNA carrying the amino acid specified by the codon in the A site arrives.

7. Termination: Steps 4-6 are repeated until a stop codon is reached.

Translation animationOne more Translation animation

If a segment of DNA is: TAC AAA GTA ACT

The mRNA strand would be: AUG UUU CAU UGA

This would code for the following amino acids:

Met Phe His Stop

Types of MutationsPoint Mutation- a change of one or just a few nucleotides in a gene. 3 Main Types of Point Mutations:

•Substitution- one nucleotide is replaced by

another.•Insertion –

an extra nucleotide is added.•Deletion-

a nucleotide is omitted.

Mutations can be “Silent”When a substitution mutation in a base pair

does not result in a change in the sequence of amino acids in a protein

Mutations can be “Neutral”A change in a base pair results in an amino acid

change, but the new amino acid has the same chemical properties as the old amino acid. (ie hydrophobic to hydrophobic; acidic to acidic)

Mutations can be “Missense”

a mutation results a change in an amino acid where the new amino acids has a different property than the old amino acid. The protein with the new primary structure may have reduced or no activity.

Mutations can be “Nonsense”

A mutation results in a new “stop” translation condon formed before the naturally occurring one. Translation is stopped prematurely and a shortened protein is made.

Mutations can result in “Frameshifts”

A deletion or insertion of one base results in a change in the translational reading frame