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Mitosis and
Protein Synthesis
Cell Division
Occurs in humans and other organisms
at different times in their life.
 Cell Division differs depending on type
of organism:

– Eukaryotic organisms undergoing growth,
development, repair, or asexual
reproduction divide by mitosis.
• EXAMPLE: new hair, nails, skin, liver, cells,
etc… are produced.
Interphase
 95%
of cell cycle in interphase
 Cells replicate their DNA
Mitosis
Mechanism
used by cells to
replicate DNA and produce
identical cell copies.
5% of cell cycle is mitosis
Happens in all cells
Mitosis

It is broken down into 5 major stages:
– Prophase
– Metaphase
– Anaphase
– Telophase
Prophase
1st phase of Mitosis
 Nucleolus breaks down &
Nuclear membrane disappears
 Chromosomes condense –
sister chromatids stay
attached by the centromere
 Kinetochore fibers form

Metaphase
2nd phase of Mitosis
 The kinetochore fibers move the
Chromosomes to the equator (middle)
– Each chromatid is attached to the
fibers at the centromere.

Anaphase
3rd phase of Mitosis
 Centromeres split
 Sister chromatids are pulled apart to opposite
poles of the cell
 After chromatids separate, they are
considered to be individual chromosomes.

Telophase
4th phase of Mitosis
 Chromosomes begin to uncoil back into
chromatin state.
– Cytokinesis
• Cytoplasm divides
• Two new daughter cells are now separate
 2 nuclear membranes form around each set of
chromosomes.
 Nucleolus forms in
each of the newly
formed cells.

Mitosis Animation
PROTEIN
SYNTHESIS
 Protein
synthesis involves two
types of nucleic acids:
DNA (deoxyribonucleic acid)
RNA (ribonucleic acid)
Differences Between DNA and
RNA
DNA
double-stranded
RNA
single-stranded
sugar = deoxyribose
sugar = ribose
bases = A,T,C,G
bases = A,U,C,G
(uracil takes the
place of thymine)
RNA

RNA, like DNA, is a polymer formed by
a sequence of nucleotides
Free
Nucleotide
DNA
Replication
DNA Replication
DNA copies
itself exactly
(Occurs within the nucleus)
 Any mistake in copying =
mutation
Basic Facts of DNA Replication
Complementary
base pairing
makes replication
possible
C-G
A-T
Basic Facts of DNA Replication
One side of DNA
molecule is a
template for
making the other
side (strand)
DNA Replication
Step 1:
 Uncoil & unzip DNA
molecule
 This occurs because of a
weak hydrogen bond
between the bases.
DNA Replication
Step 2:
Enzyme brings in complementary N-bases
DNA Replication
Each new DNA
molecule contains
one old strand &
one new strand
DNA Replication Animation
Protein Synthesis
involves two processes:
1.
Transcription: the copying of the genetic
instructions (DNA) into a molecule of mRNA
2.
Translation: mRNA is used to assemble an
amino acid sequence into a polypeptide
(protein)
Pathway to Making a
Protein
DNA
Transcription
mRNA
Translation
Protein
Transcription
Process in which genetic instructions
are transcribed (rewritten) to form an
RNA molecule.
 occurs in the nucleus of eukaryotic cells
 Transcription occurs in 3 major steps:

Step 1:
 RNA polymerase (enzyme) binds to the
promoter.
– Promoter – a specific nucleotide sequence of
DNA that initiates transcription. (“START”
sequence)

DNA strand unwinds and separates
Step 2:
 RNA polymerase adds free RNA
nucleotides that are complementary to
the nucleotides on one of the DNA
strands.
Complementary Pairings:
EXAMPLE:
DNA
RNA
A
=
U
T
=
A
C
=
G
G
=
C
A
=
U
C
=
G
Step 3:
 RNA polymerase reaches the
“termination signal” sequence of
nucleotides that marks the end of
transcription.
 RNA polymerase releases both the DNA
strand and the newly formed RNA
strand.

The RNA made during transcription can
be any of the three types of RNA:
1. messenger RNA (mRNA)
2. transfer RNA (tRNA)
3. ribosomal RNA (rRNA)
Transcription Animation
Translation (Protein Synthesis)
RNA  protein
Translation
occurs in the cytoplasm of the cell, at
the ribosome
 All RNAs needed in translation

– mRNA, tRNA, and rRNA
Messenger RNA (mRNA)

Carries coded instructions for protein
synthesis (translation)
– From the DNA in the nucleus to the
ribosome
The genetic code

Codons
– instructions for making a
protein, a series of three nucleotides
on the mRNA
– Each codon signifies
start, stop, or an amino acid
The genetic code
Transfer RNA (tRNA)
Brings amino acids to the ribosome so it
can build proteins
 It has Anticodons

– 3 nucleotide sequence
complementary to the mRNA
codon
Ribosomal RNA (rRNA)

Makes up ribosomes
Translation
Step 1:
mRNA from nucleus Through cytoplasm
to the ribosome
mRNA start codon AUG signals beginning
of protein

Translation
Step 2:

tRNA with the complementary anticodon
carries amino acid (a.a.) to bind to the
codon
Translation
Step 3:

Enzymes help form peptide bonds
between amino acids
Peptide bond
Translation
Step 4:
This continues until a stop codon is
reached
 Protein is released into the cell

Translation Animation