Cell division requires DNA replication • Before cells can divide, DNA must be replicated! – One identical copy of mother cell’s genes to both daughters produced – They each need the genetic code (DNA) to make their proteins later in life
• Why do cells divide? – Body growth, development – Tissue repair • Some divide often: skin, intestines • Some divide slowly: liver • Some don’t divide: nervous, muscle (skeletal and cardiac) • Cell cycle phases – Interphase: cell division prep • G 1 (→G 0 ) • S- phase… make DNA copy • G 2 – M phase: division • Mitosis: nuclear • Cytokinesis: cytoplasm The cell cycle
– DNA polymerase makes new polymer by complementary base pairing • Covalently binds free nucleotides from nucleoplasm • Only adds nucleotides in 1 direction, produces 1. Continuous leading strand 2. Discontinous lagging strand - Okasaki fragments – DNA ligase: connects Okasaki fragments • Enzymes needed!! – DNA helicase unwinds, separates DNA strands from histones • DNA replication begins at replication fork • Old strands= templates DNA replication in S-phase
DNA replication DNA replication • Two identical DNA molecules formed from original DNA • Semi-conservative replication : 1 old and 1 new strand/ final DNA molecule • New DNA rewinds around histone proteins • Important that new DNA is not damaged or broken!
Mitosis • After G 2 • Separates the duplicated DNA into two identical nuclei – Daughter cells have same DNA as mother • Phases: PMAT – Prophase – Metaphase – Anaphase – Telophase Self-study
Mitosis and cytokinesis Cleavage furrow: actin microfilaments in contractile ring Self-study
• Cell destiny 1. To remain alive and function without dividing 2. To grow and divide 3. To die • Killed by harmful agents or mechanical damage • Self-destruct via apoptosis – programmed cell death, cell self-implodes, no mess made • In normal adult tissue= balance between cell division and cell loss/destruction Fates of new daughters…… Self-study
Normal cell division Depends on: • Cell cycle checkpoints and integrity of DNA • Many chemicals: growth factors and regulatory and repair proteins • Telomere shortening leads to aging • Genes : balance between stimulating and inhibiting cell division – Proto-oncogenes : favor cell division – Repressor genes: (i.e. p53) inhibit cell division – Mutations? Self-study
Abnormal cell division/growth • Tumors : cells fail to follow cell cycle rules, - uncontrolled cell division – Benign tumor: have capsule, confined to original location, surgically remove – Malignant tumor (cancer): no capsule, invade surrounding tissue, • Metastasis : malignant cells break off and travel to distant tissue Self-study
Chapter 3 Part II Protein synthesis DNA is needed to make proteins!
Overview: From DNA to protein • DNA directs its own replication (we just saw that!) • DNA directs protein synthesis (we will see this now!) • DNA : genetic instructions – Gene : segments of DNA code for RNA → protein • DNA → mRNA ( transcription ) – Nucleus • mRNA → protein ( translation ) – Cytoplasm, ribosomes
Let’s start with the BIG picture!!!
- Fall '16
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