Transcript DNA – Deoxyribonucleic Acid

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!
A G C C T A G G G A T A G
T C G G A T C C C T A T C
• Transferring that information into an
Amino Acid Sequence (a PROTEIN) is the
trick.
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 Furrow
divides 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
HAPLOID
DIPLOID
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
• 2n1n
VARIATION!
Meiosis I
Meiosis II
•
•
•
•
Prophase II
Metaphase II
Anaphase II
Telophase II
• Separation of sister
chromatids
• 1n1n
• 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