Chapter 6 A Tour of the Cell

Size of a Nanometer demo ells/scale/ ells/scale/ Glucose =.9 nm Ribosome = 30 nm Mitochondria = 4000 nm long Skin Cell = 30,000 nm long = 30 um 1000 nm = 1 um

Light Microscope - LM Uses visible light to illuminate the object. Relatively inexpensive type of microscope. Can examine live or dead objects.

Resolution Ability to detect two discrete points as separate from each other. As Magnification increases, Resolution decreases. LM working limits are X.

Limitations - LM Miss many cell structures that are beyond the magnification of the light microscope. Need other ways to make the observations.

Light Microscope Variations Fluorescence: uses dyes to make parts of cells “glow”. Phase-contrast: enhances contrasts in density. Confocal: uses lasers and special optics to focus only narrow slides of cells.

Before After

Electron Microscopes Use beams of electrons instead of light. Invented in 1939, but not used much until after WWII. Electron beam scans surface of the sample, exciting electrons which have their signals detected by a device that translates the pattern of electrons into an electronic signal to a video screen.

TEM – tracheal cell, long cilia were cut longitudinally, others cut to reveal cross section SEM rabbit trachea covered in cilia

Advantages Much higher magnifications. Magnifications of 50,000X or higher are possible. Can get down to atomic level in some cases.

Disadvantages Need a Vacuum. High cost of equipment. Specimen preparation. Specimen must be dead

Other Tools for Cytology (study of Cells) Cell Fractionation – break the cell apart and separate out the pieces based on their density.

Cell Fractionation

History of Cells Robert Hooke - Observed cells in cork. Coined the term "cells” in Robert Brown, discovered the nucleus M.J. Schleiden, all plants are made of cells T. Schwann, all animals are made of cells.

Cell Theory All living matter is composed of one or more cells. The cell is the structural and functional unit of life. All cells come from cells. U5x6Nxnw

Types of Cells Prokaryotic - lack a nucleus and other membrane bounded structures. Eukaryotic - have a nucleus and other membrane bounded structures.

Both Have: Membrane Cytoplasm Ribosomes (but the size is different)

ProkaryoticEukaryotic Nucleus

Prokaryotic Eukaryotic

Basic Cell Organization Membrane Nucleus Cytoplasm Organelles

Animal Cell

Plant Cell

Membrane Separates the cell from the environment. Boundary layer for regulating the movement of materials in/out of a cell.

Cytoplasm or Cytosol Cell substance between the cell membrane and the nucleus. The “fluid” part of a cell. Composed of water, dissolved salts and organic molecules (molecules that contain Carbon, dissolved proteins, and the cytoskeleton)

Organelle Term means "small organ”. Formed body (or compartment) in a cell with a specialized function. Important in organizational structure of cells.

Organelles - function Way to form compartments in cells to separate chemical reactions. Keeps various enzymes separated in space.

You must be able to: Identify the major organelles Give their structure Give their function

Nucleus Most conspicuous organelle. Usually spherical, but can be lobed or irregular in shape.

Structure Nuclear membrane Nuclear pores Nucleolus Chromatin

Nuclear Membrane Double membrane separated by a nm space. Inner membrane supported by a protein matrix which gives the shape to the nucleus.

Nuclear Pores Regular “holes” through both membranes. 100 nm in diameter. Protein complex gives shape. Allows materials in/out of nucleus.

Nucleolus Dark staining area in the nucleus per nucleus. Ribosomes are made here

Chromatin Chrom: colored - tin: threads DNA and Protein in a “loose” format. Will form the cell’s chromosomes.

Nucleus - Function Control center for the cell. Contains the genetic instructions.

Ribosomes Structure: 2 subunits made of protein and rRNA. No membrane. Function: protein synthesis.

Subunits Large: 45 proteins 3 rRNA molecules Small: 23 proteins 1 rRNA molecule

Locations Free in the cytoplasm - make proteins for use in cytosol. Membrane bound - make proteins that are exported from the cell.

Endomembrane System Membranes that are related through direct physical continuity or by the transfer of membrane segments called vesicles.

Endomembrane System

Endoplasmic Reticulum Often referred to as ER. Makes up to 1/2 of the total membrane in cells. Often continuous with the nuclear membrane.

Structure of ER Folded sheets or tubes of membranes. Very “fluid” in structure with the membranes constantly changing size and shape.

Types of ER Smooth ER: no ribosomes. Used for lipid synthesis, carbohydrate storage, detoxification of poisons/drugs. Stores Ca ions Rough ER: with ribosomes. Makes secretory proteins.

Golgi Apparatus Structure: parallel array of flattened cisternae. (looks like a stack of Pita bread) 3 to 20 per cell. Likely an outgrowth of the ER system.

Function of Golgi Bodies Processing - modification of ER products (proteins for secretion). Distribution - packaging of ER products (proteins for secretion) for transport.

Vesicles Small sacs of membranes that bud off the Golgi Body. Transportation vehicle for the modified ER products.

Lysosome Single membrane. Made from the Golgi apparatus.

Function Breakdown and degradation of cellular materials. Contains enzymes for fats, proteins, polysaccharides, and nucleic acids. Over 40 types known.

Lysosomes Important in cell death. Missing enzymes may cause various genetic enzyme diseases. Examples: Tay-Sachs,

Vacuoles Structure - single membrane, usually larger than the Golgi vesicles. Function - depends on the organism.

Protists Contractile vacuoles - pump out excess water. Food vacuoles - store newly ingested food until the lysosomes can digest it.

Plants Can have a large single vacuole when mature making up to 90% of the cell's volume. Function Water regulation. Storage of ions. Storage of hydrophilic pigments. (e.g. red and blues in flower petals).

Function: Plant vacuole Used to enlarge cells and create turgor pressure. Enzymes (various types). Store toxins. Coloration.

Microbodies Structure: single membrane. Often have a granular or crystalline core of enzymes.

Function Specialized enzymes for specific reactions. Peroxisomes: break down fatty acids, detoxify, adds H2 to toxis (it has enzymes in it that convert H2O2 to H20) Glyoxysomes: convert lipids into sugars (useful for plant seeds)

Enzymes in a crystal

Mitochondria Structure: 2 membranes. The inner membrane has more surface area than the outer membrane. Matrix: inner space. Intermembrane space: area between the membranes.

Inner Membrane Folded into cristae. Amount of folding depends on the level of cell activity. Contains many enzymes. ATP generated here.

Function Cell Respiration - the release of energy from food. Major location of ATP generation. “Powerhouse” of the cell. Comment – be careful NOT to overuse this phrase.

Mitochondria Have ribosomes (small size). Have their own DNA. Can reproduce themselves. Likely were independent cells at one time.

Chloroplasts Structure - two outer membranes. Complex internal membrane. Fluid-like stroma is around the internal membranes.

Inner or Thylakoid Membranes Arranged into flattened sacs called thylakoids. Some regions stacked into layers called grana. Contain the green pigment chlorophyll.

Function Photosynthesis - the use of light energy to make food.

Chloroplasts Contain ribosomes (small size). Contain DNA. Can reproduce themselves. Often contain starch. Likely were independent cells at one time (cyano-bacteria).

Cytoskeleton Network of rods and filaments in the cytoplasm.

Functions Cell structure and shape. Cell movement. Cell division - helps build cell walls and move the chromosomes apart.

Cytoskeleton Components Microtubules Microfilaments Intermediate Filaments

Microtubules Structure - small hollow tubes made of repeating units of a protein dimer. Size - 25 nm diameter. Can be 200 nm to 25  m in length.

Microtubules Regulate cell shape. Coordinate direction of cellulose fibers in cell wall formation. Tracks for motor molecules.

Microtubules Form cilia and flagella. Movement of organelles and chromosomes within the cell

Dynein Protein (Type of microtubule) A contractile protein. Uses ATP. Creates a twisting motion between the microtubules causing the structure to bend or move.

Microfilaments 5 to 7 nm in diameter. Structure - two intertwined strands of actin protein.

Microfilaments are stained green.

Functions Muscle contraction. Cytoplasmic streaming. Pseudopodia. Cleavage furrow formation. Maintenance and changes in cell shape.

Intermediate Filaments Fibrous proteins that are super coiled into thicker cables and filaments nm in diameter. Made from several different types of protein.

Functions Maintenance of cell shape. Hold organelles in place.

Cytoskeleton Very dynamic; changing in composition and shape frequently. Cell is not just a "bag" of cytoplasm within a cell membrane.

Cell Wall Nonliving jacket that surrounds some cells. Found in: Plants Prokaryotes Fungi Some Protists

Plant Cell Walls All plant cells have a Primary Cell Wall. Some cells will develop a Secondary Cell Wall.

Primary Wall Thin and flexible. Cellulose fibers placed at right angles to expansion. Placement of fibers guided by microtubules.

Secondary Wall Thick and rigid. Added between the cell membrane and the primary cell wall in laminated layers. May cover only part of the cell; giving spirals. Makes up "wood”.

Middle Lamella Thin layer rich in pectin found between adjacent plant cells. Glues cells together.

Cell Walls May be made of other types of polysaccharides and/or silica. Function as the cell's exoskeleton for support and protection.

Extracellular Matrix - ECM Fuzzy coat on animal cells. Helps glue cells together. Made of glycoproteins and collagen. Evidence suggests ECM is involved with cell behavior and cell communication.

Why Are Cells So Small? Cell volume to surface area ratios favor small size. Nucleus to cytoplasm consideration (control). Metabolic requirements. Speed of diffusion.