Chapter 6: Tour of the Cell

I. Introduction

A. Microscopes:

1. Light Microscope

2. Magnification

3. Resolution or Resolving Power

4. Electron Microscope (EM)

a. Scanning Electron Microscope (SEM)

b. Transmission Electron Microscope (TEM)

Pictures of Electron Microscope at Miami

TEM SEM

Surface of a cell from a rabbit trachea covered with cilia

Cross section of cilia

Longitudinal section of cilia

B. Cell Fractionation – a biochemical approach to studying cells

1. Take cells apart to study individual parts

2. Use a centrifuge

a. The “Pellet” contains large structures

b. The “Supernatant” (liquid) contains the small parts

c. Process is repeated with supernatant each time

d. Result - pure samples of cell structures for study.

C. Cell Sizes vary with their function

1. Vary from bacteria to bird’s eggs

2. What limits cell size

a. minimum it must house DNA, proteins, and organelles to survive

b. maximum is limited by SA:V

Cell Fractionation

Cell Size

D. Prokaryotic Cells (pro “before”, karyon “kernel”)

1. No nucleus

a. DNA is coiled into a nucleoid region.

b. A plasma membrane encloses the cytoplasm

c. A cell wall surrounds the plasma membrane of most bacteria (not all) to protect it and maintain shape

d. A capsule surrounds the cell wall in some proks to further protect

sticky outer coat; helps glue cell to surfaces

e. Pili are short projections from surface of cell. Some proks have these

help attach to surfaces and involved in reproduction

f. Flagella are longer projections that help cell move

E. Eukaryotic cells are partitioned into functional compartments (Eu “true”)

1. Membranous Organelles

a. benefits for having membranes around organelles are:

conditions for specific rxns are maintained

processes can occur simultaneously thru cell

increases cells total membrane area

Prokaryotic Eukaryotic

F. Differences between a Prokaryotic cell and a Eukaryotic cell

CharacteristicsCharacteristics ProkProk EukEuk

Nuclear Envelope Absent Present

Chromosomes Single, Circular Multiple, Linear

Golgi Apparatus Absent Present

Endoplasmic Reticulum Absent Present

Lysosomes, Peroxisomes Absent Present

Mitochondria Absent Present

Chlorophyll Not in chloroplasts In Chloroplasts

Ribosomes Small Large

Cytoskeleton Fibers Absent Present

Flagella Lack Microtubules Contain Microtubules

Prokaryotic

Eukaryotic

G. Difference between plant and animal cells:

Plant cell Animal cellNo Lysosomes (this is questionable…there may be evidence that they do)

Has Lysosomes

No Centrioles Has a pair of centrioles

Different structure of flagella Different structure of flagella

Thick rigid cell wall No cell wall

Rectangular shape No rigid shape (roundish)

Has chloroplasts No chloroplasts

Large central vacuole Some have small vacuoles

THEY ARE BOTH EUKARYOTIC!!!!!!!!!!!!!

Animal Cell

Plant Cell

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

A. Endoplasmic Reticulum

1. Rough ER structure vs. Smooth ER structure

2. Two functions of Rough ER

a. makes more membrane (for ER and other organelles)

b. makes proteins that are secreted by the cell (ie. Antibody)

1. As polypeptide is made…it goes into ER

2. Carbs attached = glycoprotein

3. When they leave they are packaged into a transport vesicle (budding from ER)

4. Goes to Golgi Apparatus for further “folding”

3. Function of the Smooth ER

a. Makes lipids (fatty acids, phospholipids and steroids) depending on type of cell

b. Metabolizes carbs and detoxification of drugs/poison (liver)

c. Stores calcium ions (necessary for muscle contraction)

B. Golgi Apparatus

1. Consists of flattened sacs layered like pancakes

a. Has polarity because the membranes on either end differ in thickness and molecular composition

b. “Cis” face receives molecules (side facing nucleus)

c. “Trans” face gives rise to vesicles that pinch off and travel to other sites (side away from nucleus)

d. # of sacs correlates with how many proteins are secreted

2. Function: a. Receives and modifies products from ER b. Makes some polysaccharides

III. Organelles of the Endomembrane System (Theme: Structure Function)

A. Nucleus

1. DNA located here

2. DNA + histones forms long fibers = chromatin

3. Each fiber is a “chromosome” when coiled

4. Nuclear Envelope

a. double membrane of proteins and lipids that contains pores (therefore it is semipermeable)

5. Nucleolus

a. where ribosomes are made

b. may have more than one depending on species and stage in cell cycle

6. Nuclear pores

B. Ribosome

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

a. Subunits Large: 45 proteins; 3 rRNA moleculesSmall: 23 proteins; 1 rRNA molecule

2. Function: protein synthesis.3. Location: Free in the cytoplasm - make proteins for use

in cytosol. On ER - make proteins that are exported from the cell.

C. Lysosome

1. Membrane sac of digestive enzymes

2. Four functions of a lysosome

a. digest food vacuoles in protists

b. destroy bacteria (macrophages)

c. Recycle cell’s organic material (“autophagy”)

d. programmed destruction (embryonic development)

3. Needs membrane around it….why?

4. Lysosomal Storage Diseases

D. Peroxisomes

1. Contain enzymes that transfer Hydrogen from various substrates to Oxygen, producing Hydrogen peroxide (H2O2)

a. In the liver, they detoxify alcohol

b. break down fatty acids for use in mitochondria (seeds)

E. Vacuole

1. Larger than vesicles

2. Functions: (depends on the organism)

a. Food (protists – store newly ingested food until lysosomes can digest it.b. Contractile (protists – pump extra water out) c. Central – (plants) stores proteins (seeds), chemicals, pigments, poisons, water, waste…makes up to 90% of the cell's volume.d. Tonoplast - the name for the vacuole membrane.

IV. Energy Converting Organelles

A. Chloroplasts

1. In a family of “Plastids” -- other members include:

a. Chromoplast – store hydrophobic pigments like carotene

b. Amyloplast/Leukoplast – store starch

2. Where photosynthesis takes place – converting solar energy to chemical energy

3. Contain chlorophyll and enzymes

4. More information: a. Contain ribosomes. b. Contain DNA. c. Can reproduce themselves. d. Often contain starch. e. May have been independent cells at one time.

4. Basic structure:

a. Thylakoid (one disc)– light rxn occurs here

b. Grana (stack of discs)

c. Stroma (thick fluid)– dark rxn or Calvin cycle occurs here

d. Intermembrane space (space between outer and inner membrane of chloroplast)

B. Mitochondria

1. There could be one to thousands depending on metabolic level (function: to make ATP)

2. Enclosed in an envelope of 2 membranes

a. each a phospholipid bilayer with embedded proteins

b. Outer membrane is smooth

c. Inner membrane is convoluted with foldings called “cristae”

3. Two internal compartments

a. Intermembrane space (region between inner and outer membrane)

b. Mitochondrial matrix (enclosed by inner membrane)

4. Other info:a. Have ribosomes.b. Have their own DNA.c. Can reproduce themselves.d. May have been independent cells at one time.

V. The Cytoskeleton and Related Structures

A. Cytoskeleton

1. Network of fibers extending throughout the cytoplasm

2. Gives mechanical support to cell

3. Regulation of biochemical activities (still being researched)

4. Involved in types of cell movement

a. Move cilia and flagella

b. Cause muscle cells to contract

c. Vesicles travel via “monorails” created by cytoskeleton

d. Manipulates plasma membrane to form food vacuoles during phagocytosis

e. Cytoplasmic streaming

5. Made of three main types of fibers

a. Microtubules

b. Miccrofilaments

c. Intermediate filaments

SEE PAGE 113 FOR DIFFERENCES SEE PAGE 113 FOR DIFFERENCES (slide 35)(slide 35)

B. Centrosomes and Centrioles

1. Centrosome = made from microtubules, region located near the nucleus

a. Function as compression-resisting “girder”

2. Centrioles (pairs located within the centrosome)

a. Composed of nine sets of triplet microtubules arranged in a ring

b. organize microtubule assembly (not essential)

Intermediate filament

MicrofilamentCytoskeleton

Microtubule

Page 113 in your book

C. Cilia and Flagella of Eukaryotes

1. Function to move cell or move things around cell

2. Differ in size, number, and beating patterns

3. Share structure -- “9 + 2” pattern

a. Core of microtubules covered in an extension of the plasma membrane

b. Nine doublets of microtubules are arranged in a ring

c. Center of ring are two single microtubules

d. Doublets are connected to center by radial spokes

e. Each doublet has pairs of arms connecting it to neighboring doublet

f. Attached to cell by a “basal body” which is structurally similar to a centriole

4. How they move:

a. The arms attaching each doublet contain a large protein called “dynein”

b. A dynein arm performs a complex cycle of movements caused by changes in the conformation of the protein. ATP provides the nrg.

c. Dynein Walking: arms grab neighboring doublet and pull so that the doublets slide past each other in opposite directions.

D. Centrioles

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

2. Found in animal cells

3. 9 sets of triplet microtubules

4. Help in cell division

E. Basal Bodies

1. Same structure as a centriole

2. Anchor cilia and flagella.

Basal Body

VI. Cell Surfaces and Junctions

A. Cell Wall 1. Nonliving jacket that surrounds some cells. (plants, proks, fungi, some protists)

2. protects cell, maintains its shape and prevents excessive uptake of water

3. Thicker than plasma membrane

4. Composition differs from species to species, but design is consistent

a. cellulose is embedded in a matrix of other polysaccharides and protein

B. Extracellular Matrix of animal cells (ECM) 1. Fuzzy coat on animal cells. 2. Helps glue cells together. 3. Made of glycoproteins and collagen. 4. Evidence suggests ECM is involved with cell behavior and cell

communication.

Glycoproteins: a. Collagen b. fibronectins – bind to receptor proteins called integrins c. integrins – span the membrane and bind on the cytoplasmic side

C. Intercellular junctions

1. Integrates cells into higher levels of structure and function

a. tissues, organs, and organ systems

2. Plants Cells

a. cell walls are perforated with channels called “plasmodesmata” (desmos means “to bind”)

b. Cytoplasm passes through plasmodesmata…thus making the plant one living continuum.

c. Macromolecules reach these channels via fibers of cytoskeleton

d. Allows for communication between cells.

3. Animal Cells (see handout)a. Tight junctions

Very tight fusion of the membranes of adjacent cells.Seals off areas between the cells.Prevents movement of materials around cells.

b. DesmosomesBundles of filaments which anchor junctions between cells.Does not close off the area between adjacent cells.Coordination of movement between groups of cells

c. Gap JunctionsOpen channels between cells, similar to

plasmodesmata. Allows “communication” between cells.

TightDesmosomes

Gap junction