Mitosis andProtein 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 interphaseCells replicate their DNA

Mitosis

Mechanism used by cells to replicate DNA and produce identical cell copies.

5% of cell cycle is mitosisHappens 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

PROTEINSYNTHESIS

Protein synthesis involves two types of nucleic acids:

DNA (deoxyribonucleic acid)

RNA (ribonucleic acid)

Differences Between DNA and RNA

DNA RNAdouble-stranded 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

FreeNucleotide

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 - GA - 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 moleculeThis occurs because of a weak hydrogen bond between the bases.

DNA ReplicationStep 2:Enzyme brings in complementary N-bases

Each new DNA molecule contains one old strand &

one new strand

DNA Replication

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 Pathway to Making a ProteinProtein

DNADNA

mRNAmRNA

ProteinProtein

Transcription

Translation

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

TranslationStep 1: mRNA from nucleus Through cytoplasm

to the ribosome

mRNA start codon AUG signals beginning of protein

tRNA with the complementary anticodon carries amino acid (a.a.) to bind to the codon

TranslationStep 2:

Enzymes help form peptide bonds between amino acids

TranslationStep 3:

Peptide bond

TranslationStep 4: This continues until a stop codon is

reached Protein is released into the cell

Translation Animation