Cells: The Living Units Chapter 3
Cells Basic structural and functional units of life.
Plasma Membrane: Structure
Plasma Membrane A.K.A. cell membrane
The Fluid Mosaic Model Fluid bilayer of lipids Mostly phospholipids hydrophilic “head” Charged Attracted to water Located on inner and outer sides of membrane hydrophobic “tail” Uncharged (nonpolar) Avoid water Center of membrane
Lipid Bilayer
The Fluid Mosaic Model(cont’d) Cholesterol Stabilizes membrane Glycolipid With attached sugar group
The Fluid Mosaic Model(cont’d) Protein Responsible for most of specialized functions of membrane
The Fluid Mosaic Model(cont’d) Protein (cont’d) Integral At least some portion of their structure within the lipid bilayer Most are transmembrane proteins Have both hydrophilic and hydrophobic regions
The Fluid Mosaic Model(cont’d) Protein(cont’d) Peripheral Attached to the outside of plasma membrane (attached to integral)
The Fluid Mosaic Model(cont’d) Protein(cont’d) Functions of proteins in membrane: Transport Enzymatic activity Receptors Intercellular joining Cell to cell recognition Help maintain cell shape
Plasma Membrane
The Fluid Mosaic Model(cont’d) Carbohydrates Glycocalyx “sugar covering” At cell surface Biological markers
Specialization of Plasma Membrane Microvilli Extensions of plasma membrane that increase its surface area for absorption
Plasma Membrane: Function
Membrane Functions Physical barrier Plays a role in cellular communication Contains receptors Regulates materials in and out of the cell Selectively, or differentially permeable Passive transport – movement w/o energy input from cell – uses kinetic energy of molecules Active transport - requires ATP
Passive Transport No extra input of energy required Simple Diffusion From greater to lesser concentration (down a concentration gradient) Net diffusion ceases when reaches equilibrium
Passive Transport Simple Diffusion (cont’d) Lipid soluble molecules diffuse directly through lipid bilayer. Most water-soluble particles unable to diffuse –charged small molecules or ions, can pass through channel proteins (selective).
Simple Diffusion
Passive Transport (cont’d) Diffusion- Facilitated diffusion Molecules that can’t dissolve in lipid bilayer or are too large to pass through membranes – pass through with help from carrier proteins (integral). Carriers are selective
Facilitated Diffusion
Passive Transport (cont’d) Diffusion - Osmosis diffusion of water across a selectively permeable membrane
Passive Transport (cont’d) Diffusion- Osmosis (cont’d) Hypotonic solutions – net gain of water Concentration of solute less outside cell
Passive Transport (cont’d) Diffusion- Osmosis (cont’d) Hypertonic solutions – net loss of water Concentration of solute more outside cell
Passive Transport (cont’d) Diffusion- Osmosis (cont’d) Isotonic solutions – neither loss nor gain Concentration equal on both sides
Passive Transport (cont’d) Filtration Force - difference in the number of collisions that occur among molecules in different regions Pressure gradient
Active Transport Cell uses ATP to move substances across membrane Materials unable to pass in desired direction by diffusion Too large May not be able to move in the fat core Move uphill against concentration gradient
Active Transport(cont’d) 2 important examples of active transport: Solute pumping Vesicular transport
Active Transport - Solute Pumping Depend on carrier proteins and ATP Carries amino acids, some sugars, and most ions Example: Sodium-Potassium (Na+-K+) Pump
Active Transport – Sodium-Potassium (Na+-K+) Pump Necessary for normal transmission of nerve impulse Transport Na+ and K+ ions against concentration gradient
Active Transport - Na+-K+ Pump (cont’d) Binding sites for Na+ and ATP on intracellular surface Binding sites for K+ on extracellular surface 3 Na+ move outward and 2 K+ move inward for each molecule of ATP hydrolyzed
Active Transport - Na+-K+ Pump (cont’d) For normal intracellular Na+ concentration, the pump rate limited by availability of internal Na+ Increased intracellular Na+ concentration increases pump transport activities
Active Transport - Vesicular Transport Large particles and molecules transported across plasma membrane. Requires use of ATP 2 major types: Exocytosis – Moves large particles out of cell Ejects hormones, secretions, wastes
Exocytosis
Active Transport - Vesicular Transport (cont’d) Endocytosis – Brings large particles or substances into cell Phagocytosis “cell eating” Large particles, like bacteria or dead body cells White blood cells – phagocytes
Active Transport - Vesicular Transport (cont’d) Endocytosis (cont’d) Pinocytosis “cell drinking” liquids Important in cells that function in absorption
Generating and Maintaining Resting Membrane Potential Voltage that exists across the plasma membrane during resting state of cells (inside more negative) Determined mainly by concentration gradients of Na+ and K+ and selectively permeable membrane Greater outward diffusion of K+ leads to voltage at membrane This maintained by operation of Na+-K+ pump.
Internal Cell Structure
The Cell
The Cytoplasm
Cytoplasm Cellular material between the plasma membrane and the nucleus. Cytosol – fluid Organelles – metabolic machinery of cell Inclusions – nonliving stored nutrients
Organelles
Mitochondria Cellular aerobic respiration (ATP) “Powerhouse of the cell”
Ribosomes Site of protein synthesis Some float free, some attached to ER.
Endoplasmic Reticulum (ER) Pathways Rough ER (RER) Studded w/ ribosomes Makes all proteins secreted by cells Membrane factory Synthesize cholesterol and phospholipids
ER (cont’d) Smooth ER (SER) Continuation of RER, but no protein synthesis (no ribosomes) Synthesis of cholesterol Fat metabolism & transport Detoxification of drugs Steroid synthesis Breakdown of glycogen
The Cell
Golgi Apparatus Prepares and packages cellular products (proteins, membranes)
Lysosomes Intracellular digestion Worn-out organelles and tissues Viruses, bacteria, toxins Breakdown bone to release Ca++ into blood
Peroxisomes Protect cells from destructive effects of free radicals and other toxins
The Cell
Cytoskeleton Rods running through cytosol Microtubules Determine overall shape of cell and distribution of organelles Intermediate filaments Ropelike Resist mechanical stress Microfilaments Movement of cell parts Produce change in cell shape
Centrioles Form mitotic spindle
Centrioles (cont’d) Basis of cilia and flagella Cilia – whiplike, cellular extensions Occurs in large numbers in some cells Moves substances along cell surface
Centrioles (cont’d) Flagella – longer extension of cell surface Used to propel cell
The Cell
Nucleus Control center of cell Transmit genetic information Instructions for protein synthesis Nuclear membrane (envelope) Large pores Regulate the passageway into and out of nucleus Nucleoli Site of ribosome synthesis Chromatin Proteins and DNA Threadlike Become coiled chromosomes during cell division
The Nucleus
The Environment of the Cell
Extracellular Environment Cellular products gases, salts, & food particles proteins, hormones, & vitamins secretions of the cell ECF (extracellular fluid) syrup like substance of water, products, and other substances plasma (heart & blood vessels) interstitial (between the cells)
Intracellular Environment The substance of a cell is called protoplasm, which is composed of: water, proteins, carbohydrates, nucleic acids, lipids, & electrolytes plasma (cell) membrane cytoplasm nucleus
Cell Life Cycle
Chromosomes
Chromosomes Humans - 46 chromosomes. Homologous chromosomes or homologues Same size and shape and carry genes for the same traits One from each parent 22 homologous pairs plus 2 sex chromosomes
Human Karyotype
Cell Life Cycle From cell formation to cell reproduction 2 major periods: Interphase Cell division
Cell Life Cycle
Interphase Nondividing phase Cytoplasmic growth DNA replication Prepare for division
Interphase
Cell Division Essential for body growth and repair 2 major phases: Mitosis – division of nucleus Cytokinesis – division of cytoplasm
Mitosis Prophase Chromosomes thicken and become visible Centrioles move to opposite poles Nuclear membrane disappears Spindle fibers begin to develop
Prophase
Mitosis (cont’d) Metaphase Spindle fibers continue to expand Chromosomes line up along the central plane
Metaphase
Mitosis (cont’d) Anaphase Chromatids are separated by the shrinking of spindle fibers
Anaphase
Mitosis (cont’d) Telophase Chromatids reach opposite poles Spindle fibers disappear Nucleus begins to reappear Chromosomes uncoil - become chromatin Cytokinesis begins
Telophase
Cytokinesis Cytoplasm divides Offspring approximately equal in size and genetically identical
Cytokinesis
Meiosis Only in reproductive cells 2 consecutive nuclear divisions Produce 4 cells, each w/ half the chromosome no. of parent Each division - stages similar to mitotic division, but with certain differences.
Meiosis (cont’d) Interphase - same
Meiosis (cont’d) Prophase I – Homologous chromosomes line up – tetrad (4 strands) – synapsis Crossing over
Crossing Over
Meiosis (cont’d) Metaphase I Tetrads line up at central plane Random orientation
Meiosis (cont’d) Anaphase I Each homologous chromosome moves to poles
Meiosis (cont’d) Telophase I Nuclear membrane forms Cytokinesis – 2 cells
Meiosis (cont’d) Brief interphase
Meiosis (cont’d) Meiosis II Same course as mitotic division 4 phases PMAT II End result – 4 cells – half the original chromosome no.
Prophase II Metaphase II
Anaphase II Telophase II
DNA Replication
DNA Deoxyribonulceic acid Store and transmit genetic information Directs protein synthesis
DNA Nucleotide 3 parts: sugar molecule called deoxyribose phosphate group one of four nitrogenous bases: adenine (A) guanine (G) cytosine (C) thymine (T)
Complementary base pairing Rules for pairing of nitrogenous bases are: Cytosine - Guanine Adenine - Thymine
Structure of DNA
DNA Replication Helix uncoils Chains separate by enzymes called helicase. Each chain - template for a new nucleotide chain, using base-pairing rules. DNA polymerase, an enzyme, helps form new chains. Product – 2 new exact copies of the original DNA molecule are produced.
Protein Synthesis
RNA Ribonucleic acid Contains uracil (U), instead of thymine. Pairs with adenine. Ribose sugar Single stranded
RNA (cont’d) 3 types of RNA: Messenger RNA (mRNA) Carries instructions for making proteins from DNA in the nucleus to ribosomes Each 3 base sequence (codon) calls for a particular amino acid to be built in the protein.
RNA (cont’d) Transfer RNA (tRNA) Transfers amino acids to ribosome and recognizes codons on mRNA strand specifying its amino acid.
RNA (cont’d) Ribosomal RNA (rRNA) Forms ribosomes, where proteins are made
Protein Synthesis Transcription Instructions for protein synthesis are copied from DNA to mRNA. Base pairing rules: C-G A-U When complete, mRNA leaves the nucleus and goes to the ribosomes.
Protein Synthesis (cont’d) Translation Occurs at ribosomes Reading of mRNA (codon) by tRNA (anticodon) Genetic Code: Each codon codes for a specific amino acid.
Protein Synthesis (cont’d) Translation (cont’d) tRNA (anticodon) is complementary Brings amino acid to ribosome Pairs with mRNA codons Peptide bonding of the amino acids into protein.
Translation
Cells and Aging
Theories on Aging Little chemical insults Free radicals causing damages Antioxidant Vitamins – may prevent damage Vit C Vit E Presence of toxic chemicals in blood Temporary absence of needed substances May be cumulative Finally upsetting balance in body
Theories on Aging (cont’d) External factors Genetics – aging clock Disorders of immune system