chapter 5 cell structure

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Chapter 5 Cell Structure

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Chapter 5 Cell Structure. Warning!!. Much of this chapter is covered in Biology I so the pacing will be rapid. Focus on what is new to you while you review what is already familiar. - PowerPoint PPT Presentation

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Page 1: Chapter 5              Cell Structure

Chapter 5 Cell Structure

Page 2: Chapter 5              Cell Structure

Warning!!

Much of this chapter is covered in Biology I so the pacing will be rapid.

Focus on what is new to you while you review what is already familiar.

Page 3: Chapter 5              Cell Structure

“Faith is a fine invention when

gentlemen can see, but microscopes are

prudent in an emergency.”

Emily Dickinson

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Cell Biology or Cytology

Cyto = cell - ology = study of

Should use observations from several types of microscopes to make a total picture of how a cell is put together.

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Light Microscope - LM

Uses visible light to illuminate the object.

Relatively inexpensive type of microscope.

Can examine live or dead objects.

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Light Microscope

Occular Lens

Objective Lens

Stage with specimen

Light Source

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Resolution

Ability to detect two discrete points as separate from each other.

As Magnification increases, resolution decreases.

LM working limits are 100 - 1000X.

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Limitations - LM

Miss many cell structures that are beyond the magnification of the light microscope.

Need other ways to make the observations.

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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.

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Electron Microscopes

Use beams of electrons instead of light.

Invented in 1939, but not used much until after WWII.

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TEM SEM

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Advantages

Much higher magnifications. Magnifications of 50,000X or

higher are possible. Can get down to atomic level

in some cases.

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Disadvantages

Need a Vacuum. Specimen must stop the

electrons. High cost of equipment. Specimen preparation.

Page 16: Chapter 5              Cell Structure

Transmission Electron Microscope - TEM

Sends electrons through thinly sliced and stained specimens.

Gives high magnification of interior views. Many cells structures are now visible.

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TEM Limitations

Specimen dead. Specimen preparation uses

extreme chemicals so artifacts are always a concern.

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Scanning Electron Microscope - SEM

Excellent views of surfaces. Produces 3-D views. Live specimens possible.

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Other Tools for Cytology

Cell Fractionation Chromatography Electrophoresis

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Cell Fractionation

Disrupt cells. Separate parts by

centrifugation at different speeds.

Result - pure samples of cell structures for study.

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Cell Fractionation

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Chromatography

Technique for separating mixtures of chemicals.

Separates chemicals by size or degree of attraction to the materials in the medium.

Ex - paper, gas, column, thin-layer

Page 23: Chapter 5              Cell Structure

Electrophoresis

Separates mixtures of chemicals by their movement in an electrical field.

Used for proteins and DNA.

Page 24: Chapter 5              Cell Structure

History of Cells

Robert Hooke - Observed cells in cork.

Coined the term "cells” in 1665.

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History of Cells 1833 - Robert Brown,

discovered the nucleus. 1838 - M.J. Schleiden,

all plants are made of cells. 1839 - T. Schwann,

all animals are made of cells. 1840 - J.E. Purkinje, coined

the term “protoplasm”.

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Cell Theory

All living matter is composed of one or more cells.

The cell is the structural and functional unit of life.

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R. Virchow

“Omnis cellula e cellula” All cells are from other cells.

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Types of Cells

Prokaryotic - lack a nucleus and other membrane bounded structures.

Eukaryotic - have a nucleus and other membrane bounded structures.

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Both Have:

Membrane Cytosol Ribosomes (but the size is

different)

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Prokaryotic Eukaryotic

Nucleus

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Prokaryotic

Eukaryotic

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Why Are Cells So Small?

Cell volume to surface area ratios favor small size.

Nucleus to cytoplasm consideration (control).

Metabolic requirements.

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Basic Cell Organization

Membrane Nucleus Cytoplasm Organelles

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Animal Cell

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Plant Cell

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Membrane

Separates the cell from the environment.

Boundary layer for regulating the movement of materials in/out of a cell.

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Cytoplasm or Cytosol

Cell substance between the cell membrane and the nucleus.

The “fluid” part of a cell. Exists in two forms: gel - thick sol - fluid

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Organelle

Term means "small organ” Formed body in a cell with a specialized function.

Important in organizational structure of cells.

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Organelles - function

Way to form compartments in cells to separate chemical reactions.

Keeps various enzymes separated in space.

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You must be able to:

Identify the major organelles Give their structure Give their function

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Nucleus

Most conspicuous organelle. usually spherical, but can be

lobed or irregular in shape.

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Structure

Nuclear membrane Nuclear pores Nucleolus Chromatin

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Nuclear Membrane

Double membrane separated by a 20-40 nm space.

Inner membrane supported by a protein matrix which gives the shape to the nucleus.

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Nuclear Pores

Regular “holes” through both membranes.

100 nm in diameter. Protein complex gives shape. Allows materials in/out of

nucleus.

Page 47: Chapter 5              Cell Structure

Nucleolus

Dark staining area in the nucleus.

0 - 4 per nucleus. Storage area for ribosomes.

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Chromatin

Chrom: colored - tin: threads DNA and Protein in a “loose”

format. Will form the cell’s chromosomes.

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Nucleus - Function

Control center for the cell. Contains the genetic

instructions.

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Ribosomes

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

Function: protein synthesis.

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Subunits

Large: 45 proteins 3 rRNA molecules

Small: 23 proteins 1 rRNA molecule

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Locations

Free in the cytoplasm - make proteins for use in cytosol.

Membrane bound - make proteins that are exported from the cell.

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Endomembrane System

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

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Endomembrane System

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Endoplasmic Reticulum

Often referred to as ER. Makes up to 1/2 of the total

membrane in cells. Often continuous with the

nuclear membrane.

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Structure of ER

Folded sheets or tubes of membranes.

Very “fluid” in structure with the membranes constantly changing size and shape.

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Types of ER

Smooth ER: no ribosomes. Used for lipid synthesis,

carbohydrate storage, detoxification of poisons.

Rough ER: with ribosomes. Makes secretory proteins.

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Golgi Apparatus or Dictyosomes

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.

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Function of Golgi Bodies

Processing - modification of ER products.

Distribution - packaging of ER products for transport.

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Golgi Vesicles

Small sacs of membranes that bud off the Golgi Body.

Transportation vehicle for the modified ER products.

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Lysosome

Single membrane. Made from the Golgi

apparatus.

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Function

Breakdown and degradation of cellular materials.

Contains enzymes for fats, proteins, polysaccharides, and nucleic acids.

Over 40 types known.

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Lysosomes

Important in cell death. Missing enzymes may cause

various genetic enzyme diseases.

Examples: Tay-Sachs, Pompe’s Disease

Page 69: Chapter 5              Cell Structure

Vacuoles

Structure - single membrane, usually larger than the Golgi vesicles.

Function - depends on the organism.

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Protists

Contractile vacuoles - pump out excess water.

Food vacuoles - store newly ingested food until the lysosomes can digest it.

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Plants

Large single vacuole when mature making up to 90% of the cell's volume.

Tonoplast - the name for the vacuole membrane.

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Function

Water regulation. Storage of ions. Storage of hydrophilic

pigments. (e.g. red and blues in flower petals).

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Function: Plant vacuole

Used to enlarge cells and create turgor pressure.

Enzymes (various types). Store toxins. Coloration.

Page 76: Chapter 5              Cell Structure

Microbodies

Structure: single membrane. Often have a granular or

crystalline core of enzymes.

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Function

Specialized enzymes for specific reactions.

Peroxisomes: use up hydrogen peroxide.

Glyoxysomes: lipid digestion.

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Enzymes in a crystal

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Mitochondria

Structure: 2 membranes. The inner membrane has more surface area than the outer membrane.

Matrix: inner space. Intermembrane space: area

between the membranes.

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Inner Membrane

Folded into cristae. Amount of folding depends

on the level of cell activity. Contains many enzymes. ATP generated here.

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Function

Cell Respiration - the release of energy from food.

Major location of ATP generation.

“Powerhouse” of the cell.

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Mitochondria

Have ribosomes (small size). Have their own DNA. Can reproduce themselves. May have been independent

cells at one time.

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Chloroplasts

Structure - two outer membranes.

Complex internal membrane. Fluid-like stroma is around

the internal membranes.

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Inner or Thylakoid Membranes

Arranged into flattened sacs called thylakoids.

Some regions stacked into layers called grana.

Contain the green pigment chlorophyll.

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Function

Photosynthesis - the use of light energy to make food.

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Chloroplasts

Contain ribosomes (small size). Contain DNA. Can reproduce themselves. Often contain starch. May have been independent

cells at one time.

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Plastids

Group of plant organelles. Structure - single membrane. Function - store various

materials.

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Examples

Amyloplasts/ Leucoplasts - store starch.

Chromoplasts - store hydrophobic plant pigments such as carotene.

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Ergastic Materials General term for other

substances produced or stored by plant cells.

Examples: Crystals Tannins Latex Resins

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Cytoskeleton

Network of rods and filaments in the cytoplasm.

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Functions

Cell structure and shape. Cell movement. Cell division - helps build cell

walls and move the chromosomes apart.

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Components

Microtubules Microfilaments Intermediate Filaments

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Microtubules

Structure - small hollow tubes made of repeating units of a protein dimer.

Size - 25 nm diameter with a 15 nm lumen. Can be 200 nm to 25 m in length.

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Tubulin

Protein in microtubules. Dimer - and tubulin.

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Microtubules

Regulate cell shape. Coordinate direction of

cellulose fibers in cell wall formation.

Tracks for motor molecules.

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Microtubules

Form cilia and flagella. Internal cellular movement. Make up centioles, basal

bodies and spindle fibers.

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Cilia and Flagella

Cilia - short, but numerous. Flagella - long, but few. Function - to move cells or to

sweep materials past a cell.

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Cilia and Flagella

Structure - 9+2 arrangement of microtubules, covered by the cell membrane.

Dynein - motor protein that connects the tubules.

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Dynein Protein

A contractile protein. Uses ATP. Creates a twisting motion

between the microtubules causing the structure to bend or move.

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Centrioles

Usually one pair per cell, located close to the nucleus.

Found in animal cells. 9 sets of triplet microtubules. Help in cell division.

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Basal Bodies

Same structure as a centriole. Anchor cilia and flagella.

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Basal Body

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Microfilaments

5 to 7 nm in diameter. Structure - two intertwined

strands of actin protein.

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Microfilaments are stained green.

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Functions

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

cell shape.

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Intermediate Filaments

Fibrous proteins that are super coiled into thicker cables and filaments 8 - 12 nm in diameter.

Made from several different types of protein.

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Functions

Maintenance of cell shape. Hold organelles in place.

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Cytoskeleton

Very dynamic; changing in composition and shape frequently.

Cell is not just a "bag" of cytoplasm within a cell membrane.

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Cell Wall

Nonliving jacket that surrounds some cells.

Found in: Plants Prokaryotes Fungi Some Protists

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Plant Cell Walls

All plant cells have a Primary Cell Wall.

Some cells will develop a Secondary Cell Wall.

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Primary Wall

Thin and flexible. Cellulose fibers placed at

right angles to expansion. Placement of fibers guided by

microtubules.

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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”.

Page 126: Chapter 5              Cell Structure

Middle Lamella

Thin layer rich in pectin found between adjacent plant cells.

Glues cells together.

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Cell Walls

May be made of other types of polysaccharides and/or silica.

Function as the cell's exoskeleton for support and protection.

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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.

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Intercellular Juctions

Plants-Plasmodesmata

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Plasmodesmata

Channels between cells through adjacent cell walls.

Allows communication between cells.

Also allows viruses to travel rapidly between cells.

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Intercellular Juctions

Animals: Tight junctions Desmosomes Gap junctions

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Tight Junctions

Very tight fusion of the membranes of adjacent cells.

Seals off areas between the cells.

Prevents movement of materials around cells.

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Desmosomes Bundles of filaments which

anchor junctions between cells.

Does not close off the area between adjacent cells.

Coordination of movement between groups of cells.

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Gap Junctions

Open channels between cells, similar to plasmodesmata.

Allows “communication” between cells.

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Summary

Answer: Why is Life cellular and what are the factors that affect cell size?

Be able to identify cellular parts, their structure, and their functions.