Cell Structure & Functions

• Prokaryotic Cells

  • generally smaller (.1-10 microns)
  • no nucleus -> DNA is a circular chromosome called a plasmid
  • has ribosomes
  • no membrane-bound organelles
  • all bacteria are prokaryotes
  • found everywhere - even in extreme environments
  • ex. bacteria
• Eukaryotic cells

  • larger & more complex (10-100 microns)
  • has a nucleus
  • has organelles
  • all plants, animals, fungus and protists are made out of eukaryotic cells
  • ex. humans, mushrooms, algae
• Evolution of eukaryotic cells

  • the endosymbiotic theory
  • eukaryotic cells are complex cells with mitochondria & chloroplast
  • states that eukaryotic cells arose from living communities formed by prokaryotic (bacteria) organisms
• Basic cell structure

  • Eukaryotic cells have 2 general regions:
  • cell membrane: thin flexible barrier around cells
  • cytoplasm: inside the cell membrane, but not including the nucleus - contains organelles
• Basic cell structure

  • Cytoplasm contains several organelles:
  • Nucleus
  • Contains chromatin (DNA) which controls cell activities through the proteins that get made from the DNA code
  • nucleolus
  • dark dot in the nucleus
  • form ribosomes
  • nuclear envelope
  • double membrane
  • pores for RNA & ribosomes to get to the cytoplasm
• Basic cell structure

  • Cytoplasm contains several organelles:
  • Rough endoplasmic reticulum (ER)
  • large internal membrane system
  • contain ribosomes which make proteins
  • inside ER - proteins are transport & modified after they are made so they can be functional
  • Ribosomes
  • assemble proteins following coded instructions from DNA
  • found either on the ER or free in the cytoplasm
• Basic cell structure

  • Cytoplasm contains several organelles:
  • Golgi apparatus
  • the "post office" of the cell
  • organized group of membranes with enzymes to modify, sort and package proteins that travel from the ER after production
  • proteins can be used in the cell or be packaged and shipped out of the cell to be used somewhere else in the organism (like hormones)
• Basic cell structure

  • Cytoplasm contains several organelles:
  • Lysosomes
  • Small sacs of enzymes that...
  • digest food molecules like proteins, carbs & lipids into monomers like amino acids and glucose
  • break down worn out organelles and recycle the molecular parts for use in the cell
  • only in animal cells
• Basic cell structure

  • Cytoplasm contains several organelles:
  • Vacuole
  • the cell's "storage unit"
  • stores water, carbohydrates, & salts
  • plant cells - large central vacuole filled with water
  • the pressure in the vacuole allows the plant to remain rigid and "stand up" and support flowers and leaves
  • this pressure is called turgor pressure
  • animals cells have smaller, clear vacuoles
• Basic cell structure

  • Cytoplasm contains several organelles:
  • Mitochondrion
  • converts chemical energy in food into molecules that are more convenient for cells to use
  • glucose from food is converted into ATP (usable chemical energy)
  • Cytoskeleton
  • network of protein fibers that
  • helps cell to maintain its shape
  • provides a framework supporting the cell organelles
  • forms cilia and flagellum which help cells moves
  • cilia = hairs (paramecium)
  • flagella = whip-like tail (sperm cell)
• Basic cell structure

  • Cytoplasm contains several organelles:
  • Centriole
  • 2 structures located near the nucleus that help organize chromosomes during cell division
  • only in animal cells
• Basic cell structure

  • Plant cells have a couple more organelles:
  • cell wall
  • plants, fungi, algae, and bacteria all have cell walls outside their cell membranes
  • made of cellulose
  • it supports cells by making them firm
  • protects the cells from bursting
  • chloroplast
  • located in plants & algae
  • oval organelle that contains pigment chlorophyll for photosynthesis, which synthesis fats, proteins
• Movement of material in/out of cells

  • cell membrane (all cells)
  • controls what goes in/out of the cell
  • water, oxygen, glucose, carbon dioxide, ions & hormones
  • supports/shapes the cell
  • helps with communication with other cells
  • holds organelles together
• Movement of material in/out of cells

  • cell membrane (all cells)
  • three components
  • 2 thin layers of phospholipid molecules - phospholipid bilayer
  • the non-polar fatty acid chains form the inner part of the membrane. they are lipid and repel water (hydrophobic)
  • the polar phosphate heads form the outermost and innermost (facing cytoplasm) parts of the membrane. they attract water (hydrophilic)
  • the membrane is fluid & flexible- not rigid
  • it is selectively permeable (only certain things get in/out)
• Movement of material in/out of cells

  • cell membrane (all cells)
  • three components
  • proteins
  • embedded in lipids - they are channels for the movement of materials
  • some act as receptors for signaling molecules from other cells - this is how cells communicate with each other
  • carbohydrates
  • help with cell to cell contact and communication (along with membrane proteins)

  A) protein channel

  B) protein receptors

  C) carb chains

  D) cell mem.

  E) phospholipid

  F) outside of cell

  
• Transport of material in & out of cells

  • the concentration of a solution is the mass of a solute in a given volume of solution
  • a concentration gradient means there's a difference in concentration of solution in 2 areas or sides of a membrane
  • differences in the concentration of solutions around cell affect how materials move in & out

  
• Passive transport: no energy (ATP) needed

  • diffusion
  • material move back and forth across the cell membrane from high concentration to low concentration
  • solution have reached equilibrium when the concentrations of solutes are equal
  • particles continue to diffuse across a membrane in BOTH directions - just at equal rate
  • Ex. oxygen & carbon dioxide moving through membranes of cells in lungs
• Passive transport: no energy (ATP) needed

  • Osmosis
  • the diffusion of water across a semipermeable membrane - (Water only, not solute) will move until equilibrium is reached
  • ex. water moving from soil into roots
• 3 types of solutions that affect how water moves in/out of cells

  • Isotonic
  • iso = same
  • concentration of solutes are equal on both sides of membrane
  • water moves = in both directions across membrane
  • cell stays the same size
  • Hypertonic
  • hyper = more
  • the more concentrated side of membrane (more solute)
  • water leaves a cell if it is in a hypertonic solution
  • salt water is hypertonic to cells
  • cell shrivels up which is called plasmolysis
• 3 types of solutions that affect how water moves in/out of cells

  • Hypotonic
  • hypo = low
  • the less concentrated side of a membrane (less solute and more water)
  • water enters a cell if it's in a hypotonic solution
  • fresh water is hypotonic to cells because cells have dissolved materials in them
  • cells will well which can lead to cytolysis - bursting
• Passive transport: no energy (ATP) needed

  • Facilitated diffusion
  • some molecules can't cross the lipid membrane easilt and use the help of a carrier molecule
  • size/polarity - they may be a little too bif or too polar to slip through
  • ex. water (is polar and is repelled by the membrane)
  • speed - the cell may need some molecules quickly
  • ex. glucose (after a meal)
  • molecules still move from high to low concentration
• Active transport - energy needed

  • transport of molecules that requites energy because membrane changes
  • materials can move against the concentration gradient (low to high)
  • molecular transport (pumps)
  • proteins in the cell membrane pump molecules against the gradient
  • ex. Na+ & K+ pump muscle contraction
  • bulk transport (large particles & molecules)
  • endocytosis (in)
  • cell engulfs a large amount of material by forming pockets within the cell membrane
  • result in large vacuoles in the cytoplasm
  • ex. amoeba engulfing a paramecium or white blood cells engulfing a bacterium
• Active transport - energy needed

  • exocytosis (out)
  • release of large amount of material through the cell membrane
  • ex. proteins are packaged in membranes and shipped out of cell or an amoeba packages waste and ships it out of its cell
• Cellular diversity

  • unicellular organisms - organisms that perform all cell functions & are one single cell
  • prokaryotes (no nucleus)
  • bacteria - good survival adaptations, most abundant on earth
  • eukaryotes (has nucleus)
  • some protists and fungus: euglena, amoeba, yeast
  • multicellular organisms
  • made of many cells
  • cell specialization: cells in the organism have different structures in order to complete different jobs in organisms, "division of labor"
  • increases efficiency
  • ex. fat cells - huge vacuole to store fat droplets
  • muscle cells - a lot of mitochondria
  • nerve cells - long and thin
• Cellular diversity

  • levels of organization
  • cells within organisms are classified into groups called levels:
  • cells
  • tissues: group of similar cells with a function
  • 4 main groups of tissues - muscle, epithelial, nervous, connective
  • organs: several tissues work together
  • stomach: nervous, epithelial, muscle
  • organ system: organs that work together to complete a task
• Cellular diversity

  • levels of organization
  • systems are necessary for 3 reasons:
  • a division of labor among cells
  • many individual cells can't work together without regulation & coordination
  • most cells in a multicellular organism aren't in direct contact with the environment, so it ensures that cells get the material they need (circulation, respiration)