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

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

DNA Replication Figure 3.14

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

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

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

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

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

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

Stages of Mitosis Figure 3.15, step 3 Centrioles Plasma membrane Interphase Early prophase Late prophase Nucleolus Nuclear envelope Spindle pole Chromatin Forming mitotic spindle Centromere Chromosome, consisting of two sister chromatids Fragments of nuclear envelope Spindle microtubules Figure 3.15, step 3

Stages of Mitosis Figure 3.15, step 6 Metaphase Anaphase Telophase and cytokinesis Daughter chromosomes Sister chromatids Nuclear envelope forming Nucleolus forming Spindle Metaphase plate Cleavage furrow Figure 3.15, step 6

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

Role of RNA Transfer RNA (tRNA) Ribosomal RNA (rRNA) 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

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

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

Nucleus (site of transcription) Cytoplasm (site of translation Protein Synthesis Nucleus (site of transcription) DNA mRNA specifying one polypeptide is made on DNA template mRNA leaves nucleus and attaches to ribosome, and translation begins Synthetase enzyme Amino acids Cytoplasm (site of translation ) Correct amino acid attached to each species of tRNA by an enzyme Growing polypeptide chain Nuclear pore Nuclear membrane mRNA As the ribosome moves along the mRNA, a new amino acid is added to the growing protein chain Released tRNA reenters the cytoplasmic pool, ready to be recharged with a new amino acid Direction of ribosome advance; ribosome moves the mRNA strand along sequentially as each codon is read Small ribosomal subunit Portion of mRNA already translated tRNA “head” bearing anticodon Large ribosomal subunit Peptide bond Incoming tRNA recognizes a complementary mRNA codon calling for its amino acid by binding via its anticodon to the codon Codon Ala Phe Ser Gly Met C G U A Figure 3.16