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PowerPoint® Lecture Slides prepared by Janice Meeking, Mount Royal College CHAPTER 3 Cells: The Living Units: Part A Copyright © 2010 Pearson Education, Inc. Generalized Cell • All cells have some common structures and functions • Human cells have three basic parts: • Plasma membrane—flexible outer boundary • Cytoplasm—intracellular fluid containing organelles • Nucleus—control center Copyright © 2010 Pearson Education, Inc. Chromatin Nucleolus Nuclear envelope Nucleus Smooth endoplasmic reticulum Mitochondrion Cytosol Lysosome Centrioles Centrosome matrix Cytoskeletal elements • Microtubule • Intermediate filaments Copyright © 2010 Pearson Education, Inc. Plasma membrane Rough endoplasmic reticulum Ribosomes Golgi apparatus Secretion being released from cell by exocytosis Peroxisome Figure 3.2 Plasma Membrane • The plasma membrane separates the intracellular fluid (ICF) from extracellular fluid (ECF) • The plasma membrane is semi-permeable which means that some things can cross the membrane and some things cannot Copyright © 2010 Pearson Education, Inc. Extracellular fluid Intracellular fluid Copyright © 2010 Pearson Education, Inc. Figure 3.3 Types of Membrane Transport • Passive Transport • No cellular energy (ATP) required • Substance moves down its concentration gradient • Active Transport • Energy (ATP) required • Substances are moved or“pumped” against their gradient Copyright © 2010 Pearson Education, Inc. Passive Transport • What determines whether or not a substance can passively permeate (cross) a membrane? 1. Lipid solubility of substance 2. Size of the molecule that is passing PLAY http://www.youtube.com/watch?v=JShwXBWGMyY Copyright © 2010 Pearson Education, Inc. Passive Transport • Simple diffusion • Facilitated diffusion • Osmosis Copyright © 2010 Pearson Education, Inc. Passive Transport: Simple Diffusion • Small, nonpolar, hydrophobic substances diffuse directly through phospholipid bilayer Copyright © 2010 Pearson Education, Inc. Extracellular fluid Lipidsoluble solutes Cytoplasm Copyright © 2010 Pearson Education, Inc. Figure 3.7a Passive Transport: Facilitated Diffusion • Larger, hydrophilic molecules (glucose, amino acids, ions) use carrier proteins or channel proteins to pass through the plasma membrane Copyright © 2010 Pearson Education, Inc. Hydrophilic molecules Copyright © 2010 Pearson Education, Inc. Figure 3.7b Passive Transport: Osmosis • Movement of solvent (water) across a selectively permeable membrane from where it is most concentrated to where it is less concentrated • Water diffuses through plasma membranes: • Through lipid bilayer • Through channels (aquaporins) Copyright © 2010 Pearson Education, Inc. Water molecules Lipid billayer Aquaporin Copyright © 2010 Pearson Education, Inc. Figure 3.7d Passive Transport: Osmosis • Osmolarity: The measure of total concentration of solute particles • When solutions of different osmolarity are separated by a membrane, osmosis occurs until equilibrium is reached Copyright © 2010 Pearson Education, Inc. (a) Membrane permeable to both solutes and water Solute and water molecules move down their concentration gradients in opposite directions. Both solutions have the same osmolarity: volume unchanged H2O Solute Membrane Copyright © 2010 Pearson Education, Inc. Solute (sugar) Figure 3.8a (b) Membrane permeable to water, impermeable to solutes Solute molecules are prevented from moving but water moves by osmosis. Volume increases in the compartment with the higher osmolarity. Left compartment Right compartment Both solutions have identical osmolarity, increases on the right because only water is free to move H2O Membrane Copyright © 2010 Pearson Education, Inc. Solute (sugar) Figure 3.8b Importance of Osmosis • When osmosis occurs, water enters or leaves a cell • A change in cell volume disrupts cell function Copyright © 2010 Pearson Education, Inc. Tonicity • Defined as: The ability of a solution to cause a cell to shrink or swell • Isotonic: A solution that does not cause a change in cell volume • Hypertonic: A solution that causes a cell to shrink • Hypotonic: A solution that causes a cell to swell. Copyright © 2010 Pearson Education, Inc. (a) Isotonic solutions Copyright © 2010 Pearson Education, Inc. (b) Hypertonic solutions (c) Hypotonic solutions Figure 3.9 Active Transport • The Sodium-potassium pump (Na+-K+ ATPase) is a specific example of active transport • Located in all plasma membranes • Maintains electrochemical gradients essential for functions of muscle and nerve tissues Copyright © 2010 Pearson Education, Inc. Vesicular Transport • Transports large particles, macromolecules, & fluids across plasma membranes • Is active transport = requires energy ATP • Examples: • Exocytosis—moves substances out of cell • Endocytosis—moves substances into cell Copyright © 2010 Pearson Education, Inc. ECF Cytoplasm Transport vesicle Endosome Lysosome (a) Copyright © 2010 Pearson Education, Inc. Other Organelles • Membranous structures • Nucleus with chromatin• Mitochondria – • Endoplasmic Reticulum (ER) (rough and smooth) – • Golgi Apparatus• Lysosomes- Copyright © 2010 Pearson Education, Inc. Nucleus Nuclear envelope Smooth ER Rough ER Vesicle Plasma membrane Lysosome Copyright © 2010 Pearson Education, Inc. Golgi apparatus Transport vesicle Figure 3.22 Smooth ER Nuclear envelope Rough ER Ribosomes Copyright © 2010 Pearson Education, Inc. Figure 3.18a Rough ER Phagosome ER membrane Plasma membrane Vesicle becomes lysosome Golgi apparatus Secretory vesicle Secretion by exocytosis Copyright © 2010 Pearson Education, Inc. Extracellular fluid Figure 3.20 Mitochondria • Organelle with shelflike folds called cristae • Provide most of cell’s ATP (enzymes for this process are located on cristae) Copyright © 2010 Pearson Education, Inc. Other Organelles • Non-Membranous structures • Centrioles- involved in cell division • Cytoskeleton- includes microfilaments, intermediate filaments and microtubules Copyright © 2010 Pearson Education, Inc. Centrosome matrix Centrioles (a) Copyright © 2010 Pearson Education, Inc. Microtubules Figure 3.25a Microfilaments • Function in cell motility and aid in cell shape Copyright © 2010 Pearson Education, Inc. (a) Microfilaments Intermediate Filaments (b) Intermediate filaments • Resist pulling forces on the cell and attach to desmosomes Copyright © 2010 Pearson Education, Inc. Microtubules • Most radiate from centrosome • Determine overall shape of cell and distribution of organelles Copyright © 2010 Pearson Education, Inc. (c) Microtubules Extensions of the plasma membrane • Cilia are: short, hairlike structures that move substances across cell surfaces • Flagella are: Whiplike, tails that move entire cell • Microvilli are: fingerlike extensions found on absorptive cells Copyright © 2010 Pearson Education, Inc. Power, or propulsive, stroke 1 2 3 4 Recovery stroke, when cilium is returning to its initial position 5 6 7 (a) Phases of ciliary motion. Layer of mucus Cell surface (b) Traveling wave created by the activity of many cilia acting together propels mucus across cell surfaces. Copyright © 2010 Pearson Education, Inc. Figure 3.27 Microvillus Actin filaments Terminal web Copyright © 2010 Pearson Education, Inc. Figure 3.28 The Cell Cycle • Includes: • Interphase • Period from cell formation to cell division • Three sub phases of Interphase: • G1 (gap 1)—growth and metabolism • S (synthetic)—DNA replication • G2 (gap 2)—preparation for division • Cell division (mitotic phase) Copyright © 2010 Pearson Education, Inc. S Growth and DNA synthesis G1 Growth Copyright © 2010 Pearson Education, Inc. M G2 Growth and final preparations for division Figure 3.31 DNA Replication • Helicase untwists the double helix and exposes complementary chains • Each nucleotide strand serves as a template for building a new complementary strand • DNA polymerase forms new DNA strand Copyright © 2010 Pearson Education, Inc. DNA Replication • End result: two DNA molecules formed from the original • This process is called semiconservative replication Copyright © 2010 Pearson Education, Inc. Chromosome Free nucleotides DNA polymerase Template for synthesis of new strand Leading strand Old DNA Helicase unwinds the double helix and Exposes bases Replication fork Adenine Thymine Cytosine Guanine Copyright © 2010 Pearson Education, Inc. Lleading and lagging strands are synthesized in opposite directions Lagging strand DNA polymerase Old (template) strand Figure 3.32 Cell Division • Mitotic (M) phase of the cell cycle • Essential for body growth and tissue repair • Does not occur in most mature cells of nervous tissue, skeletal and cardiac muscle Copyright © 2010 Pearson Education, Inc. Cell Division • Includes two distinct events: 1. Mitosis—four stages of nuclear division: • Prophase • Metaphase • Anaphase • Telophase 2. Cytokinesis—division of cytoplasm by cleavage furrow Copyright © 2010 Pearson Education, Inc. S Growth and DNA synthesis G1 Growth Copyright © 2010 Pearson Education, Inc. G2 Growth M Figure 3.31 Prophase • Chromosomes condense and become visible • Mitotic spindle form • Nuclear envelope fragments Copyright © 2010 Pearson Education, Inc. Early Prophase Early mitotic spindle Aster Early Prophase Copyright © 2010 Pearson Education, Inc. Chromosome consisting of two sister chromatids Centromere Figure 3.33 Microtubule Late Prophase Late Prophase Copyright © 2010 Pearson Education, Inc. Fragments of nuclear envelope Microtubule Figure 3.33 Metaphase • Chromosomes are aligned at the equator • Metaphase plate = The plane midway between the poles of the cell Copyright © 2010 Pearson Education, Inc. Metaphase Spindle Metaphase Copyright © 2010 Pearson Education, Inc. Metaphase plate Figure 3.33 Anaphase • Shortest phase • Chromosomes are pulled to opposite poles by microtubules Copyright © 2010 Pearson Education, Inc. Anaphase Anaphase Copyright © 2010 Pearson Education, Inc. Daughter chromosomes Figure 3.33 Telophase • Begins when chromosome movement stops • Nuclear membrane forms around each chromatin mass • Spindle disappears Copyright © 2010 Pearson Education, Inc. Cytokinesis • Begins during late anaphase • Ring of actin microfilaments contracts to form a cleavage furrow • Two daughter cells are pinched apart, each containing a nucleus identical to the original Copyright © 2010 Pearson Education, Inc. Nuclear envelope forming Nucleolus forming Contractile ring at cleavage furrow Telophase and Cytokinesis Telophase Copyright © 2010 Pearson Education, Inc. Figure 3.33 PROTEIN SYNTHESIS Copyright © 2010 Pearson Education, Inc. Protein Synthesis • DNA is the master blueprint for protein synthesis • Gene: Segment of DNA with blueprint for one polypeptide • Each triplet (3 base sequence) in DNA specifies an amino acid Copyright © 2010 Pearson Education, Inc. Nuclear envelope Transcription RNA Processing DNA Pre-mRNA mRNA Translation Nuclear pores Ribosome Polypeptide Copyright © 2010 Pearson Education, Inc. Figure 3.34 Roles of the Three Main Types of RNA • Messenger RNA (mRNA) • Carries instructions for building a polypeptide, from a gene in DNA to ribosomes in cytoplasm Copyright © 2010 Pearson Education, Inc. Roles of the Three Main Types of RNA • Ribosomal RNA (rRNA) • Helps form ribosome Copyright © 2010 Pearson Education, Inc. Roles of the Three Main Types of RNA • Transfer RNAs (tRNAs) • Transfer amino acids from cytoplasm to mRNA attached to ribosome to begin process of protein synthesis Copyright © 2010 Pearson Education, Inc. Transcription • Transfers triplet code into a complementary base sequence in mRNA Copyright © 2010 Pearson Education, Inc. Transcription • RNA polymerase • Enzyme that oversees synthesis of mRNA • Unwinds DNA • Adds complementary RNA nucleotides using a DNA template and joins them together • Stops when it reaches termination signal Copyright © 2010 Pearson Education, Inc. RNA polymerase Coding strand DNA Promoter region 1 Template strand Termination signal Initiation: Once transcription factors are bound to promoter, RNA pol binds promoter, unwinds DNA strands, and initiates mRNA synthesis . Copyright © 2010 Pearson Education, Inc. Figure 3.35 step 1 mRNA Template strand 2 Elongation: RNA pol moves along the template strand, elongating the mRNA transcript one base at a time. mRNA transcript Copyright © 2010 Pearson Education, Inc. Figure 3.35 step 2 3 Termination: mRNA synthesis ends when the termination signal is reached. RNA poly and mRNA transcript are released. Completed mRNA transcript Copyright © 2010 Pearson Education, Inc. RNA polymerase Figure 3.35 step 3 Steps of Translation • Converts base sequence of nucleic acids into the amino acid sequence of proteins • Involves mRNAs, tRNAs, and rRNAs Copyright © 2010 Pearson Education, Inc. Genetic Code • Each three-base sequence on DNA (triplet) is represented by a codon • Codon—complementary three-base sequence on mRNA Copyright © 2010 Pearson Education, Inc. SECOND BASE C A U UUU U UUC UUA UUG Phe Leu CUU C CUC CUA A Leu UCC UAC UCA Ser UAA UCG UAG CCU CAU CCC CCA Pro CAC CAA CCG CAG AUU ACU AAU ACC AAC AUC Ile ACA Thr AAA Met or AUG Start ACG AAG GUU GCU GAU GUC GCC GAC GUA GUG Copyright © 2010 Pearson Education, Inc. UAU CUG AUA G UCU Val GCA GCG Ala GAA GAG G Tyr UGU UGC U Cys C Stop UGA Stop A Stop UGG Trp G His Gln Asn Lys Asp Glu U CGU CGC CGA C Arg A CGG G AGU U AGC AGA AGG Ser C A Arg G GGU U GGC C GGA GGG Gly A G Figure 3.36 Translation • mRNA attaches to a small ribosomal subunit that moves along the mRNA to the start codon (AUG) • Large ribosomal unit attaches, forming a functional ribosome • Anticodon of tRNA binds to complementary codon and adds its amino acid to the forming protein chain • New amino acids are added by other tRNAs as ribosome moves along mRNA, until stop codon is reached Copyright © 2010 Pearson Education, Inc. Nucleus RNA polymerase mRNA Leu Template strand of DNA 1 After mRNA synthesis in the nucleus, mRNA leaves the nucleus and attaches to a ribosome. Energized by ATP, the correct amino acid is attached to each species of tRNA by aminoacyl-tRNA synthetase enzyme. Amino acid Nuclear pore tRNA Nuclear membrane G A A 2 Translation begins as incoming aminoacyl-tRNA recognizes the complementary codon calling for it at the A site on the ribosome. It hydrogen-bonds to the codon via its anticodon. Released mRNA Aminoacyl-tRNA synthetase Leu 3 As the ribosome moves along the mRNA, and each codon is read in sequence, a new amino acid is added to the growing protein chain and the tRNA in the A site is translocated to the P site. Ile tRNA “head” bearing anticodon Pro 4 Once its amino acid is released from the P site, tRNA is ratcheted to the E site and then released to reenter the cytoplasmic pool, ready to be recharged with a new amino acid. The polypeptide is released when the stop codon is read. E site P site G G C A site A U A C C G C U U Codon 15 Codon 17 Codon 16 Large ribosomal subunit Small ribosomal subunit Direction of Portion of mRNA ribosome advance already translated Copyright © 2010 Pearson Education, Inc. Figure 3.37 Nucleus mRNA RNA polymerase Template strand of DNA 1 mRNA leaves the nucleus and attaches to a ribosome. Leu Amino acid Nuclear pore tRNA Nuclear membrane GAA Released mRNA Aminoacyl-tRNA synthetase Copyright © 2010 Pearson Education, Inc. Figure 3.37 step 1 Leu 2 Translation begins;. Ile tRNA “head” bearing anticodon Pro E site P site G G C A site Large ribosomal subunit A U A C C G C U U Codon Codon 15 16 Codon 17 Small ribosomal subunit Direction of Portion of ribosome advance mRNA already translated Copyright © 2010 Pearson Education, Inc. Figure 3.37 step 2 Leu 3 The ribosome moves along the mRNA, and each codon is read in sequence. a new amino acid is added to the growing protein chain . Ile tRNA “head” bearing anticodon Pro E site P site G G C A site Large ribosomal subunit A U A C C G C U U Codon Codon 15 16 Codon 17 Small ribosomal subunit Direction of Portion of ribosome advance mRNA already translated Copyright © 2010 Pearson Education, Inc. Figure 3.37 step 3 Leu 3 2 Ile tRNA “head” bearing anticodon Pro 4 tRNA is released to reenter the cytoplasmic pool, ready to be recharged with a new amino acid. The polypeptide is released when the stop codon is read. E site P site G G C A site Large ribosomal subunit A U A C C G C U U Codon Codon 15 16 Codon 17 Small ribosomal subunit Direction of Portion of ribosome advance mRNA already translated Copyright © 2010 Pearson Education, Inc. Figure 3.37 step 4 Nucleus RNA polymerase mRNA Leu Template strand of DNA 1 Energized by ATP, the correct amino acid is attached to each species of tRNA by aminoacyl-tRNA synthetase enzyme. Amino acid Nuclear pore tRNA Nuclear membrane G A A 2 Released mRNA Aminoacyl-tRNA synthetase Leu 3 Ile tRNA “head” bearing anticodon Pro 4 E site P site G G C A site A U A C C G C U U Codon 15 Codon 17 Codon 16 Large ribosomal subunit Small ribosomal subunit Direction of Portion of mRNA ribosome advance already translated Copyright © 2010 Pearson Education, Inc. Figure 3.37