Lecture 2 Cell COVID (3) PDF

Structure of DNA Double stranded Structural units: nucleotides Each nucleotide is composed of: Watson & Crick ̶deoxyribose (5 C sugar) ̶inorganic phosphate (PO4) ̶1 of 4 nitrogen bases:  2 purines: Adenine (A) & Guanine (G) ...

Structure of DNA Double stranded Structural units: nucleotides Each nucleotide is composed of: Watson & Crick ̶deoxyribose (5 C sugar) ̶inorganic phosphate (PO4) ̶1 of 4 nitrogen bases:  2 purines: Adenine (A) & Guanine (G)  2 pyrimidines: Thymine (T) & Cytosine (C) Ribonucleic Acid (RNA) Similar to DNA (few differences): RNA DNA Strands Single Double Sugar Ribose Deoxyribose Pyrimidine Uracil (U) Thymine (T) 3 types: base ̶ messenger RNA (mRNA) ̶ transfer RNA (tRNA) ̶ ribosomal RNA (rRNA) Protein Synthesis Transcription: ̶copies instructions from DNA to mRNA (in nucleus) Translation: ̶ribosome reads code from mRNA (in cytoplasm) ̶assembles amino acids into polypeptide chain Processing: ̶by RER and Golgi apparatus produces protein Transcription of mRNA Step 1: gene activation Step 2: building mRNA Step 3: RNA editing Step 1: Gene Activation Uncoils DNA, removes histones Start and stop codes on DNA mark location of gene DNA strands: ̶coding strand: coding for protein ̶template strand: template for mRNA Step 2: Building mRNA RNA polymerase transcribes DNA: ̶binds to start sequence ̶reads DNA code for gene ̶binds nucleotides to form mRNA ̶mRNA duplicates DNA coding strand ̶Uracil replaces thymine Step 3: RNA Editing At stop signal, mRNA detaches from DNA: code is edited (RNA processing):  non coding regions (introns) removed  coding regions (exons) spliced together  DNA NUCLEUS mRNA mRNA moves out of the nucleus through a nuclear pore Translation Translation Step 1:  mRNA moves to a ribosome in cytoplasm Step 2:  mRNA binds to ribosomal subunits  tRNA delivers amino acids to mRNA Step 3:  tRNA anticodon binds to mRNA codon  1 mRNA codon translates to 1 amino acid Step 4:  enzymes join amino acids with peptide bonds  polypeptide chain has specific sequence of amino acids Step 5:  at stop codon, components separate Genetic Code Chemical language of DNA instructions: d e o C sequence of bases A, T (U), C, G e t c id l = 1 a i p o Tr es in a s am b 3 Mutation Change in the nucleotide sequence of a gene May change gene function abnormal protein Causes: exposure to chemicals exposure to radiation mistakes during DNA replication Transport Across Cell Membrane Overcoming the Cell Barrier Cell membrane is a barrier, but: ̶nutrients must get in ̶waste products must get out Membranes & Permeability Permeability determines what moves in and out of a cell Types of membranes: impermeable: lets nothing in or out freely permeable: lets anything pass selectively permeable: restricts movement Cell membrane Permeability Cell membrane is selectively permeable: allows some materials to move freely restricts other materials Factors affecting selectivity: size shape electrical charge lipid solubility Transport through Cell Membrane Passive: no energy required Active: requires energy and ATP 3 Categories of Transport Diffusion (passive) Carrier-mediated transport (passive or active) Vesicular transport (active) 3 Categories of Transport Diffusion (passive) Carrier-mediated transport (passive or active) Vesicular transport (active) Diffusion Passive transport Molecules mix randomly Solute spreads through solvent Concentration Gradient Concentration: amount of solute in a solvent Concentration gradient: more solute in 1 part of a solvent than another solute moves down a concentration gradient diffusion eliminates concentration gradient Factors Affecting Diffusion Rates Factors Affecting Diffusion Rates Distance the particle has to move Molecule size: smaller is faster Temperature: more heat faster motion Concentration gradient: higher gradient faster diffusion Electrical forces: opposite charges attract, similar charges repel Diffusion Across Cell Membrane Simple diffusion Channel-mediated diffusion Osmosis Simple Diffusion Materials diffuse through cell membrane: lipid-soluble compounds:  alcohols, fatty acids, and steroids  lipid-soluble drugs (e.g. halothane) dissolved gases:  oxygen and carbon dioxide Channel-Mediated Diffusion Channels: transmembrane proteins Materials pass through channels: water soluble compounds Ions Factors affecting channel-mediated diffusion: size electrical charge interaction with the channel Osmosis Diffusion of water across the cell membrane 1 Two solutions containing 2 At equilibrium, the solute 3 Osmosis can be prevented by different solute concentrations concentrations on the two sides resisting the change in volume. The are separated by a selectively of the membrane are equal. The osmotic pressure of solution B is permeable membrane. Water volume of solution B has equal to the amount of hydrostatic molecules (small blue dots) increased at the expense of that pressure required to stop the begin to cross the membrane of solution A. osmotic flow. toward solution B, the solution with the higher concentration of Volume Applied solutes (large pink dots) increased force A B Volume Original Volumes decreased level equal Water molecules Solute molecules Selectively permeable membrane How Does Osmosis Work? More solute molecules, lower concentration of water molecules Membrane must be: freely permeable to water Selectively not permeable to solutes Permeable Osmosis & Water Movement Water molecules diffuse across membrane toward solution with more solutes Volume increases on the side with more solutes Osmotic & Hydrostatic Pressures Osmotic pressure: force of a concentration gradient of water Hydrostatic pressure: force needed to block osmosis Both pressures are: opposite in direction equal in force Osmolarity & Tonicity Osmolarity: total solute concentration in an aqueous solution Tonicity: (tonos = tension) osmotic effect of a solute on a cell 2 fluids may have equal osmolarity, but different tonicity Isotonic Solution Has equal number of solutes (iso = same) Does not cause osmotic flow of water in or out of a cell A cell in an isotonic solution: ̶neither gains nor loses water ̶retains shape (biconcave red blood cells) Hypotonic Solution Has less solutes (hypo = below) Loses water through osmosis A cell in a hypotonic solution: gains water swells ruptures (hemolysis of red blood cells) Hypertonic Solutions Has more solutes (hyper = above) Gains water by osmosis A cell in a hypertonic solution: loses water shrinks (crenation of red blood cells) 3 Categories of Transport Diffusion (passive) Carrier-mediated transport (passive or active) Vesicular transport (active) Carrier-Mediated Transport Transport of ions and organic substrates across the cell membrane by binding to integral proteins (carriers) Characteristics: ̶specificity: 1 carrier protein, 1 set of substrates ̶saturation limits: rate depends on transport proteins, not substrate ̶regulation: cofactors such as hormones Cotransport & Countertransport Cotransport: = symport 2 substances move in the same direction Countertransport: = antiport 2 substances move in opposite directions Types of Carrier-Mediated Transport Facilitated diffusion (passive) Active transport (active) Secondary active transport (active) Facilitated Diffusion Carrier proteins transport molecules too large to fit through channels (e.g., glucose, amino acids): ̶ molecule binds to receptor site on carrier ̶ receptor is specific to certain molecules ̶ carrier changes shape molecules pass through Active Transport Requires energy from ATP Active transport proteins: move substrates against concentration gradient ion pumps move ions (Na+, K+, Ca+, Mg2+) exchange pump countertransports 2 ions at the same time Sodium-Potassium Exchange Pump Active transport (countertransport) Na+-K+ ATPase enzyme moves: ̶Na+ out ̶K+ in ̶1 ATP moves 3 Na+ & 2 K+ Secondary Active Transport i l i ta Fac Na+ concentration gradient drives glucose ted o transport (cotransport) u s i ATP energy pumps Na+ back out D i ff n ti v e Ac p n s Tra ort 3 Categories of Transport Diffusion (passive) Carrier-mediated transport (passive or active) Vesicular transport (active) Vesicular Transport Active transport Types: endocytosis (endo = into) exocytosis (exo = out of) Endocytosis A substance gains entry into a cell 3 categories: Phagocytosis (= Cell Is Eating) Pseudopodia (psuedo = false, podia = feet) Engulf large objects in phagosomes Digested by lysosomal enzymes Pinocytosis (= Cell Is Endosomes “drink” extracellular Drinking) fluid Receptor-Mediated Endocytosis Receptors bind ligands Coated vesicle (endosome) carries ligands and receptors into the cell e.g., cholesterol, Fe2+ Exocytosis A substance exits a cell within a vesicle Reverse of endocytosis Which of these 2 processes is called facilitated diffusion? A B Cell Life Cycle Cell Life Cycle Most of a cell’s life is spent in a non-dividing state (interphase): G-zero phase: cell functions only G1 phase: cell growth, organelle duplication, protein synthesis S phase: DNA replication and histone synthesis G2 phase: finishes protein synthesis and centriole replication G = Gap – S = Synthesis Cell Life Cycle Most of a cell’s life is spent in a non-dividing state (interphase): G-zero phase: cell functions only G1 phase: cell growth, organelle duplication, protein synthesis S phase: DNA replication and histone synthesis G2 phase: finishes protein synthesis and centriole replication Types of Cell Division Mitosis Meiosis Site e somatic cells sex cells m Daughter cells ga s somatic cells ova or sperms te # 46 (diploid) 23 (haploid) chromosomes For mitosis to start, loosely coiled Chromatin network changes into tightly coiled Chromosomes 3 Stages of Mitotic Division DNA replication: duplicates genetic material Mitosis: divides genetic material equally Cytokinesis: divides cytoplasm and organelles into 2 daughter cells 3 Stages of Mitotic Division DNA replication: duplicates genetic material Mitosis: divides genetic material equally Cytokinesis: divides cytoplasm and organelles into 2 daughter cells DNA Replication 1 2 DNA strands unwind 4 3 5 DNA polymerase attaches 8 7 6 9 complementary nucleotides Result: 2 double stranded DNA: Segment 2 each has 1 old strip + 1 new strip DNA nucleotide 6 Segment 1 7 8 1 2 KEY 3 4 5 DNA polymerase Adenine Guanine Cytosine DNA polymerase Thymine 3 Stages of Mitotic Division DNA replication: duplicates genetic material Mitosis: divides genetic material equally Cytokinesis: divides cytoplasm and organelles into 2 daughter cells Mitosis Nuclear division Divides duplicated DNA into 46 chromosomes Each chromosome: ̶consists of 2 chromatids ̶centromere: connects the 2 chromatids ̶kinetochore: protein complex around the centromere Stages of Mitosis Prophase Metaphase Anaphase Telophase Duration of Stages of Mitosis Stage 1: Prophase Centrioles Astral rays and Chromosome (two pairs) spindle fibers with two sister chromatids Early: ̶nucleoli and nuclear envelope disappear ̶each centriole moves to a cell pole ̶spindle fibers (microtubules) extend between the 2 centrioles Late: Early prophase Late prophase ̶spindle fibers attach to kinetochores Stage 2: Metaphase Chromosomal Metaphase microtubules plate Chromosomes align in a central plane (metaphase plate) Metaphase Stage 3: Anaphase Two daughter chromosomes pulled apart and drawn to opposite ends of the cell along the spindle Microtubules pull chromosomes apart apparatus. Daughter chromosomes are pulled towards opposite poles near centrioles Anaphase Stage 4: Telophase Cleavage furrow Nuclear envelopes reform Chromosomes uncoil Nucleoli reappear Cell has 2 complete nuclei Telophase 3 Stages of Mitotic Division DNA replication: duplicates genetic material Mitosis: divides genetic material equally Cytokinesis: divides cytoplasm and organelles into 2 daughter cells Cytokinesis Daughter Cytoplasm divides cells Cleavage furrow around metaphase plate Membrane closes two daughter cells Cytokinesis The stage of mitosis where the chromosomes align in the equator of the cell is called A. Prophase B. Metaphase C. Anaphase D. Telophase E. Cytokinesis The stage of mitosis where the chromosomes align in the equator of the cell is called A. Prophase B. Metaphase C. Anaphase D. Telophase E. Cytokinesis Cell Diversity & Differentiation All cells carry complete DNA instructions for all body functions Cells specialize or differentiate: by turning off all genes not needed by that cell Cell Division & Tumors Tumor (neoplasm): abnormal cell growth and division cell mass Types of tumors: benign tumor:  localized  not life threatening malignant tumor:  Invasive  may spread new tumors (metastasis)  can be fatal Oncogenes: mutated genes that cause tumors Summary Structures and functions of cells: cell membrane cytoplasm & organelles:  membranous - nonmembranous nucleus Gene activation and protein synthesis Transport across the cell membrane Cell life cycle and mitosis