Unit 2: Cell Structure and Function

All living things are composed of one or more cells

Cell: basic unit of life

All cells related by their descent from an ancestral cell

Two types: Prokaryotic and Eukaryotic

Pro: Lack internal membrane

Eu: Have internal membrane, membrane-bound organelles

  • Eukaryotic cells have a nucleus

    • Site for DNA storage

  • Two domains: Archaea and Bacteria. Prokaryotic domains

  • Eukarya: Protist, fungi, plants, animals

  • All cells possess

    • Plasma membrane: Lipid boundary for cell contents which separates it from the environment

    • Cytosol: Semifluid gel that fills the cel, site of metabolic chemical rxn’s

    • Chromosomes: Lengths of DNA that contain genes

      • Gene: Section of DNA that codes for a protein

    • Ribosomes: Small cellular parts for protein synthesis

    • Ribosomes have rRNA

    • All cells contain ribosomes which indicates common ancestry

  • Plasma membrane is selective which allows passage

    • General structure is made up of phospholipids

    • Nonpolar nature in the interior allows for nonpolar molecules and small ones to pass without any form of diffusion

  • Prokaryote: No nucleus, DNA in nucleoid region, No membrane bound, cytoplasm, cell wall

  • Eukaryotic cells: DNA bound by membranous nuclear envelope

    • Membrane bound organelles

    • Cytoplasm in the region between plasma membrane and nucleus

    • Eukaryotic cells have internal structures like organelles

    • Cytoplasm in the region between plasma membrane and nucleus

  • Eukaryotic cells have internal structures(organelles) with specific functions

    • Eukaryotic cells are much larger than prokaryotic cells

    • Metabolic req. set upper limits on cell size

    • HIGHER SA:V ratio is better than lower because it allows more contact and efficiency

  • Endoplasmic reticulum exists in two forms; smooth ER and rough ER

    • Rough ER:

    • Smooth ER: Site of cell detox and lipid

  • Golgi complex, series of membranous, flattened sacs

    • Golgi complex is responsible for modifying newly made proteins and packaging them

  • Mitochondria posses a double membrane - Outer is smooth, inner is folded and convoluted

  • Lysosomes - membranous sacs contain hydrolytic enzymes for intercellular digestion

  • Vacuoles: Membrane-bound sacs used for mostly storage

  • Chloroplasts: found in algae and plants and perform photosynthesis

  • Nucleus: control center

    • Enclosed by a nuclear envelope

    • contains chromosomes

    • Contains the region called nucleolus

  • Ribosomes: Site of protein synthesis

  • Free-floating in the cytoplasm attached(rough ER)

2.2

  • Double membrane of mitochondria allows for improved efficiency in respiration

  • Cellular respiration transfer chem energy of organic compounds into usable energy for cells. ATP

  • Mitochondrial membranes improve efficiency

  • Double membrane and convolutions of inner membrane allow for improved efficiency

  • Folded membrane provides more space for molecules that perform ATP production

  • Chloroplasts contain thylakoids

    • Stacks are called grana

    • stroma is the fluid that fills chloroplast

  • Inner convoluted inner membrane is cristae

  • Fluid inside inner membrane is matrix

  • Between inner and outer is intermembrane space

  • Lysosomes: digest, recycle APOPTOSIS

  • APOPTOSIS - cellular death when old ones are damaged or old

  • Vacuoles: Larger than vesicles different types

    • Food: fuse with lysosome in phagocytosis

    • Contractile: freshwater protists rid themselves of excess water

    • Central: Large one found in plants enclosed by a membrane called tonoplast

    • Cytoskeleton: Maintain structured of cell

    • Microtubules:

      • Composed of tubulin molecules

      • They maintan cell shape, useful in divison, move organelles

      • intermediate filaments:

      • Composed of fibrous proteins

      • Allows for muscle contractions and helps with cytokinesis in animal cells

  • Microfilaments:

  • Composed

    • Allows for muscle contractions and helps in cytokenisis in animal cells

  • Centrosomes:

  • Region near the nucleus that begins formation of spindle fibers

  • Centrioles:

    • Found in animal cells ONLY and helps with cell divison

  • Cilia: Tiny hairs, 9+2 arrangement of microtubules used for movement. Held place

  • Flagella:

    • Long whip like tail that they use for movement

    • Same 9+2 movement

    • Basal body is identicle to centriole

  • Plasmodesmata:

    Found in plant cells. Connects chem environment of two adjacent cells

  • Gap junctions: in animal cells. similar to plasmodesmata

  • Tight junctions: Found in animal cells. Prevents leakage

  • Desmosomes: Found in animals. Rivet cells in strong sheets

  • Metabolic requirements puts an upper limit on size of cells

  • SA:V ratio is CRITICAL

  • Small cells that have greater surface area and lower volume are better because more contact.

  • HIGH SA:V ratio’s allows for more efficiency

    • Exchaning materials with environment and waste removal

  • SOme cells posses convoluted membranes to increases SA:V ratio while barely increasing overall volume

  • root hair cells increase surface area for nutrient absorbtion

  • Metabolic efficiency goes down as organisms grow in size

2.4

Cell membrane establishes unique internal environment

  • Composed of dilayer phospholipids

  • Hydrophilic phosphate heads, Hydrophobic fatty acid tails

  • Hydrophilic - polar, move TOWARD aqueous solutions

  • Hydrophobic, nonpolar and move away from aqueous solutions

    • Proteins are scattered in membrane

      Peripheral - membranes exterior or interior surface

  • Integral proteins - penetrate membrane

  • Transmembrane proteins - pass completely through bilayer

  • Proteins can be hydrophilic, phobic, or charged because of r-groups

  • Steroids, glycoproteins and glycolipids are found in the membrane too.

  • Membrane components are fluid and they migrate

  • Steroids contribute to membrane fluidity to survive in changing temps

  • Glycoproteins and glycolipds help with cell identification

  • Cytoskeleton: structual framework made of proteins that helps the cell keep its shape, STRUCTURE

  • Selective permeability is caused by the cell membrane structure

    • Selective permeability: Membrane’s ability to regulate the molecules or ions that are able to pass into and out of intracellular environment

  • Hydrophobic makes it so large polar or charged molecules not be able to cross

  • Small ones can pass but slow

  • Nonpolar ones can pass with ease

  • Large require transaport proteins that accomodate to their shape, size and charge

  • Passive: Diffusion from high to low concentration

  • Active: low to high gradient that requires energy

  • Facilitated: Help with transport protein

  • Simple: For small nonpolar molecules

  • Active needs ATP from environment

2.6

  • Facilitated speeds diffusion by utilizing transport proteins

  • Aquaporins - Transport proteins specialized for water

  • Ion channels - Movement of particular ions

  • Movement of ions creates electrochemical gradient across cell membrane

  • Membrane potential polarizes membrane

Active:

  • Requires transport proteins(PUMPS)

  • Maintain concentration gradients which prevents the cell from reaching equilibrium

  • Energy is supplied in the form of ATP

  • Na+ K+ ATPase is an active transport protein in maintaining ion gradients in animal cells

2.8

  • Osmosis: Diffusion of water through selectively permeable membrane

  • Osmosis is the passive transport of water from high to low

  • Solutions are either ISOTONIC, hypertonic or hypotonic

  • Water potential is measurement that combines effect of solute concentration and pressure

  • Tonicity: Surrounding solution that causes a cell to gain or lose water

  • Isotonic is equal

  • Hypertonic is concentration greater than inside cell which causes cell to lose water because there is low water in the concentration outside

    • Hypotonic: less concentration inside than outside, outside flows into hypotonic solution

  • Osmoregulation, ability to maintain water balance with environment

  • Contractile vacuole is an adaptation possesd by freshwater protists to osmoretgulate and maintain homeostasis

Endocytosis: cell engul extracell material

phagocytosis: endocytosis of solid

pinocytosis: liquid matter

Exocytosis: reverse of encdocytosis and removes cell waste

Compartmentalization:

Mitochondria

ENDOSYMBIONT THEORY: because of double membranes in mitochondria and chloroplasts, it is believed that these organelles originated from free-living prokaryotic cells that entered into a symbiotic relationship with ancestral eukaryotic cells.