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 1 st phase of Mitosis Nucleolus breaks down & Nuclear membrane disappears Chromosomes condense – sister chromatids stay attached by the centromere Kinetochore fibers form

Metaphase 2 nd phase of Mitosis The kinetochore fibers move the Chromosomes to the equator (middle) –Each chromatid is attached to the fibers at the centromere.

Anaphase 3 rd 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 4 th 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 DNARNA double-strandedsingle-stranded sugar = deoxyribosesugar = ribose bases = A,T,C,Gbases = 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 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

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 Protein DNAmRNAProtein 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

Translation Step 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 Translation Step 2:

Enzymes help form peptide bonds between amino acids Translation Step 3: Peptide bond

Translation Step 4: This continues until a stop codon is reached Protein is released into the cell

Translation Animation