DNA – Deoxyribonucleic Acid

Nucleic Acids

Nucleotides

DNA&

RNA

Deoxyribonucleic Acid

• Double Helix connected by N-bases.

DNA Replication

• …Resulting in two molecules, each identical to the parent, and to each other.

DNA• Information is contained in the

Sequence of N-bases found along the DNA molecule – GENES!

• Transferring that information into an Amino Acid Sequence (a PROTEIN) is the trick.

A G C C T A G G G A T A GT C G G A T C C C T A T C

A 2-step Process

1. Transcription

DNA RNA

A 2-step Process

2. Translation

RNA Protein

Ok, Lets take a step back…

Cell Division

• Cells come from pre-existing cells…

• Cells need to reproduce!– Single-celled organisms -- asexual reproduction.– Multi-celled organisms – growth.

• Cell Division = Cytokinesis

• Nuclear Division =

Karyokinesis

Prokaryotes – Binary Fission

• Simple

Eukaryotes – more complex

• Chromosomes• Chromosome Structure

– Chromatin + Histones– Unduplicated– Duplicated

• Chromosome Number– Diploid

• Somatic cells (body cells)

– Haploid• Germ cells (sex cells)

Cell Cycle

Chromosome Duplication

• During S-phase = “Synthesis”

Why?....

• So that later, the sister chromatids can separate into different (new) cells!

Karyokinesis

• Mitosis– Somatic cells (body cells)– “Cloning” of genetic information – exact

copies made and distributed to new cells.– Chromosome # is retained (stays the same).

• Meiosis– Germ cells (sex cells)– Genetic information is shuffled – new cells are

each different.– Chromosome # is cut in half.

Mitosis

• Prophase

• Metaphase

• Anaphase

• Telophase

Prophase•Nuclear Envelope Disappears•Nucleolus Disappears•Chromosomes Condense

•Chromatin Chromosomes

•Spindle Fibers (Microtubules) •Attach to Centromeres•Attach to M.T.O.C.s

Metaphase

•Chromosomes line up on the ‘Metaphase Plate’

•pushed & pulled by the spindle fibers

•Spindle Apparatus well developed.

Anaphase

•Chromosomes each broken at their centromeres

•spindle fibers on each side shorten

•New (unduplicated) chromosomes move toward the M.T.O.C.s

Telophase•Chromosomes stop moving when they reach the spindle poles (at the M.T.O.C.s)•Nuclear Envelope re-forms (2x)•Nucleolus re-forms (2x)•Spindle fibers disappear•Cytokinesis

Cytokinesis

Cleavage Furrowdivides the cells

Cell Plate divides the cells

Meiosis

• Associated with Sex!

• Sexual Reproduction involves– 2 parents– Mixing of genetic information– Life cycles, with MEIOSIS & FERTILIZATION

Life Cycles

DIPLOID

HAPLOID GAMETIC

Meiosis

• Mixing of Genetic Information

• Germ Cells (Sex Cells)

• Reduction in Chromosome Number– Diploid Haploid

• 2 Divisions– Meiosis I --- P,M,A,T– Meiosis II --- P,M,A,T

• Results in 4 cells

Meiosis I

• Prophase I

• Metaphase I

• Anaphase I

• Telophase I

• Pairing and separation of Homologous Chromosomes

• Crossing Over

• Independent Assortment

• 2n1nVARIATION!

Meiosis I

Meiosis II

• Prophase II

• Metaphase II

• Anaphase II

• Telophase II

• Separation of sister chromatids

• 1n1n

• Results in 4 DIFFERENT cells.

Meiosis II

MEIOSIS -- Spermatogenesis

MEIOSIS -- Oogenesis

Stimulated by Fertilization

MITOSIS vs MEIOSIS

Ok,…back to the molecular level…

1. Transcription

• Complimentary Base Pairing.

• DNA RNA

G - C

C - G

T - A

A - U

3 Types of RNA

• mRNA = Messenger RNA– The “blueprint”

• rRNA = Ribosomal RNA– The “workbench”

• tRNA = Transfer RNA– The “truck”

mRNA – messenger RNA

• The “message” – the blueprint for the production of a polypeptide – a protein.

2. Translation

• Problem: there are only 4 N-bases, and 20 amino acids to make a protein!

• We need a TRANSLATION!

• What’s the code?

The Genetic Code

• Triplet Base Code.

• Every 3-letter word in the RNA Transcript is a CODON.

The Genetic Code

• Each CODON codes for a single Amino Acid.

The Genetic Code

See p. 207

2. Translation

• A meeting of ALL 3 types of RNA:

– mRNA – the blueprint.– rRNA – the workbench.– tRNA – the supply truck.

2. Translation• Initiation - All 3 types of RNA come together:

mRNA, rRNA, & tRNA

2. Translation• Elongation – Amino Acids are added with

the help of elongation factors (proteins).

1. Codon meets Anticodon at the ‘A’ binding site.

2. A Peptide Bond Forms between adjacent Amino Acids

Summary