Genomics to

Proteomics

DNA

Replication

Protein Synthesis

DNA Double HelixFebruary 28, 1953…

Watson and Crick created a model of DNA by using Franklin’s and Wilkins’s DNA diffraction X-ray

Deoxyribonucleic Acid

Nucleotides: building blocks of DNA (and RNA)

1. a 5-carbon deoxyribose sugar

2. a phosphate group

3. one of four nitrogenous bases: adenine (A), guanine (G), cytosine (C), or thymine (T).

DNA Nucleotides and Complementary Bases

• Bonds Hold DNA Together– Nucleotides are linked by covalent bonds. – Complementary NBs are bonded by hydrogen

bonds

• Hydrogen bonding between the complementary base pairs, G-C and A-T, holds the two strands of a DNA molecule together.

Complementary Base Pair Rules

A—T

T—A

G—C

C—G

Practice…

• Strand A

ATGCTAGCTATTC

• Strand B?

(compliment)TACGATCGATAAG

DNA Replication

• process by which DNA is copied in a cell before a cell divides

• When?– Remember the cell cycle?

• Interphase– S phase

» Synthesis of DNA is making a copy or replication!

How DNA Replication Occurs

Steps of DNA Replication

1. Replication begins with the separation of the DNA strands by helicases.

2. Then, DNA polymerases form new strands by adding complementary nucleotides to each of the original strands.

DNA Replication & Enzymes

1. Primer—RNA/enzyme starter

2. Helicase• “Unzipper”

3. DNA Polymerase• “Putter-on-er”

4. Ligase• Glues fragments on

the 1 side of DNA

DNA Replication

Each new DNAmolecule is madeof one strand ofnucleotides fromthe original DNAmolecule and onenew strand.

Prokaryotes vs. Eukaryotes

DNA Errors in Replication

• Changes in DNA are called mutations. • Enzymes proofread and repair prevent

many replication errors.– From 1/100,000,000 (from DNA

polymerase) errors1/1 billion errors• DNA Replication and Cancer

– Unrepaired mutations that affect genes that control cell division can cause diseases such as cancer.

And now a review…

DNAi replication/transcription

Protein SynthesisFrom DNA to Protein

How Protein Synthesis Works…

• DNARNAprotein.

• The sequence of nucleotidesThe sequence of nucleotides in DNA contain information

• information put to work through the production of proteins.

• Proteins fold into complex, 3-D shapes to become key cell structures and regulators of cell functions.

Enzymes

– breaking downbreaking down glucose molecules in cellular respiration, digesting food, or making spindle fibers during mitosis.

– enzymes control all the chemical enzymes control all the chemical reactions of an organism.reactions of an organism.

– Thus, by encoding the instructions for making proteins, DNA controls cellsDNA controls cells.

• The sequence of nucleotides in each gene contains information for assembling the string of amino acids that make up a single protein.

RNA

• 3rd: 4 nitrogenous bases

A U G C– Uracil forms a base pair with

adenine in RNA, just as thymine does in DNA.

RNA—nucleic acid

RNA differs from DNA in 3 ways

• 1st: RNA is single stranded—it looks like one-half of a zipper

• 2nd: The sugar in RNA is ribose

Types of RNA

1. messenger RNA (mRNA)

2. ribosomal RNA (rRNA)

3. transfer RNA (tRNA)

3 Types…3 Functions1. mRNA carries the genetic “message” from

the nucleus to the cytoplasm.

2. rRNA is the makes up most of the ribosome.

3. tRNA carries specific amino acids, helping to form proteins.

During transcription, DNA acts as a template for directing the synthesis of RNA.

Transcription

1 side of DNA is the template w/ the gene needed

1. RNA polymerase unwinds/"unzips" the DNA by breaking the hydrogen bonds between complementary nucleotides

2. RNA nucleotides are paired with complementary DNA bases.

3. RNA sugar-phosphate backbone forms with assistance from RNA polymerase.

4. Hydrogen bonds of the untwisted RNA+DNA helix break, freeing the newly synthesized RNA strand.

5. If the cell has a nucleus, the RNA is further processed and then moves through the small nuclear pores to the cytoplasm.

Translation: From mRNA to Protein

The process of converting the Info in a

sequence of nitrogenous bases in mRNA

into a sequence of amino acids in protein

is known as translation.Translation takes place at

the ribosomes in the cytoplasm.

!!! In prokaryotic cells, which have no nucleus, the mRNA is made in the cytoplasm!!!

So DNA can’t leave the nucleus…

• Eukaryotic cells: mRNA is made in the nucleus and travels to the cytoplasm

• In cytoplasm, a ribosome attaches to the strand of mRNA like a clothespin clamped onto a clothesline.

• This is the role of transfer RNA.

tRNA

Each tRNA

molecule

attaches to

only one

type of

amino acid

Amino acid

Chain of RNA nucleotides

Transfer RNA molecule

Ribosome

mRNA codon

tRNA

AnticodonAmino acid

tRNA anticodon

Methionine

TRANSLATE THIS!

CODON: TAC ACA GAC UAU GGG ACU

Start and stop

• Usually, the first codon on mRNA is AUG, which codes for the amino acid methionine.

• AUG signals the start of protein synthesis.

• When this signal is given, the ribosome slides along the mRNA to the next codon.

…or this one

TRY THESE:

AUG

CGA

AUU

Stop codon

Amino Acid Chain

• Introduction to Molecular Genealogy

And now a review…

DNAi replication/transcription

• DNA and RNA• Protein Synthesis