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