Cell Life Cycle

1. Cell Life Cycle • Cells have two major periods • Interphase • Cell grows • Cell carries on metabolic processes • Cell division • Cell replicates itself • Function is to produce more cells for growth and repair processes

2. DNA Replication • Genetic material is duplicated and readies a cell for division into two cells • Occurs toward the end of interphase • DNA uncoils and each side serves as a template

3. DNA Replication Figure 3.14

4. Events of Cell Division • Mitosis—division of the nucleus • Results in the formation of two daughter nuclei • Cytokinesis—division of the cytoplasm • Begins when mitosis is near completion • Results in the formation of two daughter cells

5. Stages of Mitosis • Prophase • First part of cell division • Centrioles migrate to the poles to direct assembly of mitotic spindle fibers • DNA appears as double-stranded chromosomes • Nuclear envelope breaks down and disappears

6. Stages of Mitosis • Metaphase • Chromosomes are aligned in the center of the cell on the metaphase plate

7. Stages of Mitosis • Anaphase • Chromosomes are pulled apart and toward the opposite ends of the cell • Cell begins to elongate

8. Stages of Mitosis • Telophase • Chromosomes uncoil to become chromatin • Nuclear envelope reforms around chromatin • Spindles break down and disappear

9. Stages of Mitosis • Cytokinesis • Begins during late anaphase and completes during telophase • A cleavage furrow forms to pinch the cells into two parts

10. Centrioles Spindlemicrotubules Centrioles Chromatin Centromere Centromere Formingmitoticspindle Plasmamembrane Chromosome,consisting of twosister chromatids Fragments ofnuclear envelope Spindlepole Nuclearenvelope Nucleolus Interphase Early prophase Late prophase Stages of Mitosis Figure 3.15, step 3

11. Nucleolusforming Metaphaseplate Spindle Cleavagefurrow Nuclearenvelopeforming Daughterchromosomes Sisterchromatids Metaphase Anaphase Telophase and cytokinesis Stages of Mitosis Figure 3.15, step 6

12. Protein Synthesis • Gene—DNA segment that carries a blueprint for building one protein • Proteins have many functions • Building materials for cells • Act as enzymes (biological catalysts) • RNA is essential for protein synthesis

13. Role of RNA • Transfer RNA (tRNA) • Transfers appropriate amino acids to the ribosome for building the protein • Ribosomal RNA (rRNA) • Helps form the ribosomes where proteins are built • Messenger RNA (mRNA) • Carries the instructions for building a protein from the nucleus to the ribosome

14. Transcription and Translation • Transcription • Transfer of information from DNA’s base sequence to the complimentary base sequence of mRNA • Three-base sequences on mRNA are called codons

15. Transcription and Translation • Translation • Base sequence of nucleic acid is translated to an amino acid sequence • Amino acids are the building blocks of proteins

16. Nucleus(site of transcription) Cytoplasm(site of translation DNA ) mRNA specifyingone polypeptideis made onDNA template Amino acids mRNA leavesnucleus andattaches toribosome, andtranslationbegins Correct aminoacid attachedto each speciesof tRNA by anenzyme mRNA Nuclear pore Nuclear membrane Synthetaseenzyme Growing polypeptide chain As the ribosomemoves along themRNA, a new aminoacid is added tothe growing proteinchain Met Gly Incoming tRNArecognizes acomplementarymRNA codon callingfor its amino acid bybinding via itsanticodon to thecodon Ser Phe Ala Peptide bond Released tRNAreenters thecytoplasmicpool, ready tobe rechargedwith a newamino acid tRNA “head” bearinganticodon Large ribosomal subunit C G G U U C G C C A U A G U C U A C Portion ofmRNA alreadytranslated Codon Direction of ribosomeadvance; ribosome movesthe mRNA strand alongsequentially as each codonis read Small ribosomalsubunit Protein Synthesis Figure 3.16