copyright © 2005 pearson education, inc. publishing as benjamin cummings a tour of the cell

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

A Tour of the Cell


INTRODUCTION TO THE CELL

Using light microscopes, scientists came up with THE CELL THEORY:

1. All living things are made of cells2. All cells come from pre-existing cells3. Cells are the basic units of structure and function

in living things.


Sizes and shapes of cells

Human height

Length of somenerve andmuscle cells

Chicken egg

Frog egg

Most plant andanimal cells

Nucleus

Most bacteria

Mitochondrion

Mycoplasmas(smallest bacteria)

Ribosome

Viruses

Proteins

Lipids

Small molecules

Atoms

Un

aid

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Lig

ht

mic

r osc

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El e

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on

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pe

Cell sizes vary with

their function


Limitations to Cell Size

• Cells divide rather than grow indefinitely.

1. DNA “Overload”

• Stores information that controls the cells function.

• As a cell increases in size, it does not make extra copies of DNA.

• The larger a cell becomes, the more demands the cell places on its DNA.


2: Exchanging Materials

• Cell membrane regulates what enters and leaves.

• Rate of exchange depends on surface area of the cell.

• Rate at which products are used and produced depends on the cells volume.

• As the cell increases, its volume increases faster than its surface area.


Cell Surface Area & Volume

• Decrease in ratio of surface area to volume Makes it difficult for the cell to move needed materials in and waste products out.


VIRUSES

• Contain either DNA or RNA• Proteins attached to outer envelope• No nucleus• No ribosomes• No cell membrane or cell wall


Very small…….. (smaller than bacteria)

Size of Viruses


Viral Reproduction

•Reproduce by inserting genetic material into their host cell.

•Turn their host cell into a virus making factory

• Antibiotics do not work on viruses

• Vaccines can be made for viruses

• Viruses mutate easily and often


Assignment

• Compare and contrast a Virus, Animal Cell, Bacterial Cell, Plant Cell. (Structural features, Methods of Reproduction, Size, Examples of each)

• Based on your comparisons, would you classify viruses as living or nonliving? Explain your reasoning in paragraph form (A minimum of 5 complete sentences.)


Cell Types

There are two kinds of cells

– Prokaryotic (bacteria, archaea)

– Eukaryotic (protists, plants, fungi, animals)

All cells share some common features

– Plasma membrane

– DNA

– ribosomes

Nucleoidregion

Prokaryotic cell

Nucleus

Co

lor i

z ed

TE

M 1

5, 0

00

Eukaryotic cellOrganelles


PROKARYOTIC CELLS

Usually relatively small & simple cells

• Do not have a membrane-bound nucleus

• DNA is coiled into a nucleoid region in the cytoplasm

• Cytoplasm includes ribosomes

• Plasma membrane

• Complex cell wall

• Capsule, pili, prokaryotic flagella in some forms


Bacteria Shapes

Prokaryoticflagella

Ribosomes

Capsule

Cell wall

Plasmamembrane

Nucleoid region (DNA)

Pili

Prokaryotic Cell


EUKARYOTIC CELLS

• Partitioned into functional compartments

• Organelles are able to maintain their own environments.

• Larger than prokaryotic cells

• Distinguished by a True Nucleus


ANIMAL CELLS

– Are bounded by the plasma membrane alone

– Lack a cell wall

– Contain centrioles and lysosomes

– Often have flagella

Roughendoplasmicreticulum

Smoothendoplasmicreticulum

Nucleus

Flagellum

Lycosome

Centriole

Not in mostplant cells

Peroxisome

Microtubule

Intermediatefilament

Microfilament

Cytoskeleton

Golgiapparatus

Ribosomes

Plasma membrane

Mitochondrion


PLANT CELLS

– Are bounded by both a plasma membrane and a rigid cellulose cell wall

– Have a central vacuole and chloroplasts

– Usually lack centrioles, lysosomes, and flagella

Not inanimalcells

Golgiapparatus

Nucleus

Centralvacuole

Chloroplast

Cell wall

Mitochondrion

Peroxisome

Plasma membrane

Rough endoplasmicreticulum

Smooth endoplasmicreticulum

Ribosomes

Microtubule

Intermediatefilament

Microfilament

Cytoskeleton


Assignment

• Create 2 Venn diagram comparing the following cell structures:

1.Eukaryotic vs Prokaryotic Cell

2.Plant vs. Animal Cell

• Draw and label a plant and animal cell.


Nucleus

The nucleus is the cell's genetic control center

• The nucleus contains the cell's DNA

• The nucleus is separated from the cytoplasm by the nuclear envelope

– Pores in the envelope control flow of materials in and out

Chromatin

Nucleolus

Pore

Nucleus

Two membranesof nuclear envelope

Roughendoplasmicreticulum

Ribosomes


Endomembrane System

Overview: Many cell organelles are connected through the endomembrane system

• The endomembrane system is a collection of membranous organelles

– Divide the cell into compartments

– Work together in the synthesis, storage, and export of molecules


Smooth E.R.

• Lacks attached ribosomes

– Synthesizes lipids

– Processes materials such as toxins and drugs in liver cells

– Stores and releases calcium ions in muscle cells


Rough E.R.

• Contains ribosomes

• Manufactures membranes

• Modifies and packages proteins that will be

- Transported to other organelles

- Secreted by the cell

Smooth ER

Rough ER

Nuclearenvelope

Ribosomes

Smooth ER Rough ER

TE

M 4

5,0

00


Golgi Apparatus (Golgi Bodies)

• Consists of stacks of flattened membranous sacs

• Receives and modifies substances manufactured by ER

• Ships modified products to other organelles or the cell surface

Golgiapparatus

“Receiving” side ofGolgi apparatus

Transportvesiclefrom ER

New vesicleforming

“Shipping”side of Golgiapparatus Transport

vesicle fromthe Golgi

Golgi apparatus

TE

M 1

30,0

00


Lysosomes

• Sacs of enzymes that form from the Golgi apparatus

• Function in digestion within a cell

• Destroy bacteria that have been ingested into white blood cells

• Recycle damaged organelles

LE 4-10b

Lysosome

Nucleus

TE

M 8

,50

0

Lysosome containingtwo damaged organelles

TE

M 4

2,5

00

Mitochondrion fragment

Peroxisome fragment


Vacuoles

• General maintenance of the cell

• Plant cells contain a large central vacuole

– Has lysosomal and storage functions

• Some protists have contractile vacuoles

– Pump excess water out of cell

Centralvacuole

Nucleus

Chloroplast

Co

lori

zed

TE

M 8

,700

Nucleus

LM

650

Contractilevacuoles

Transport vesiclefrom ER to GolgiRough ER

Nucleus

Smooth ER Nuclear envelope Golgi apparatus

Lysosome

Vacuole

Plasmamembrane

Transport vesicle fromGolgi to plasma membrane

ChloroplastStroma

Inner and outermembranes

Granum

Intermembranespace

TE

M 9

,750

Chloroplasts convert solar energy to chemical energyAre found in plants and some protists


MITOCHONDRIA

• Found in nearly all eukaryotic cells

• Are the “powerhouses” of the cell

– Carry out cellular respiration

– Harvest chemical energy from food

Mitochondrion

Intermembranespace

Outermembrane

Innermembrane

Cristae

Matrix TE

M 4

4,88

0


THE CYTOSKELETON AND RELATED STRUCTURES

The cell's internal skeleton helps organize its structure and activities

• The cytoskeleton is network of three types of protein fibers

– Microfilaments

– Intermediate filaments

– Microtubules


Cilia/Flagella

• Eukaryotic cilia and flagella are locomotor appendages that protrude from certain cells

• Move when microtubules bend

• Move whole cells or materials across the cell surface


Bell Ringer: What regulates what enters and leaves the cell?

The Working Cell The Working Cell


CELL MEMBRANE

Controls what moves in and out of the cell

Semi-permeable: “picky/selective” regarding what it lets in and out.

Made of two layers of phospholipids: LIPID BILAYER

Outsideof cell


PHOSPHOLIPID BILAYER

Membrane phospholipids form a bilayer

• Phospholipids are the main structural components of membranes

– 2 nonpolar hydrophobic fatty acid "tails”

– 1 phosphate group attached to the hydrophilic glycerol "head“

• Proteins and other molecules are embedded in a framework of phospholipids


Hydrophilicheads

Hydrophobictails

Water

Water


Membranes are selectively permeable

• Small molecules, and hydrophobic (non-polar) molecules can easily pass through the membrane.

• Large or hydrophilic (polar) molecules cannot get through without help.


Extracellularmatrix

Glycoprotein

Carbohydrate

Plasmamembrane

Microfilamentsof cytoskeleton

Phospholipid

Cholesterol

Proteins

Cytoplasm

Glycolipid


Bell Ringer

• If I were to spray an air freshener in the front of the classroom, would someone in the back of the room eventually smell it? Explain why.


PASSIVE TRANSPORT

• Molecule diffuses down a concentration gradient (from high to low)

1. Diffusion is the tendency for particles to spread out evenly in an available space

– From an area of high concentration to an area of low concentration

– O2 and CO2 diffuse easily


EquilibriumMolecules of dye Membrane


Transport proteins may facilitate diffusion across membranes

2. Facilitated diffusion

– Transport proteins help substances diffuse down a concentration gradient

Solutemolecule

Transportprotein


3. Osmosis is the diffusion of water across a

membrane– From an area of low solute concentration– To an area of high solute concentration– Until the solution is equally concentrated

• Direction of movement is determined by the difference in total solute concentration


• Osmoregulation is the control of water balance.

– Isotonic solution: solute concentration is the same in the cell and in the solution.

• No osmosis occurs

• Animal cell volume remains constant; plant cell becomes flaccid (not firm)

Water Balance


– Hypotonic solution: solute concentration is greater in the cell than in the solution

• Cell gains water through osmosis

• Animal cell lyses; plant cell becomes swollen

– Hypertonic solution: solute concentration is lower in the cell than in the solution

• Cell loses water through osmosis

• Animal and plant cell become shriveled.


Isotonic solution Hypotonic solution Hypertonic solution

H2O H2O

(1) Normal (2) Lysed

H2O

H2O H2O H2O

Animalcell

Plantcell

(4) Less Firm (5) Swollen (6) Shriveled (plasmolyzed)

(3) Shriveled

Plasmamembrane

H2O

H2O


Active Transport

Cells expend energy for active transport

• Cells move solutes against a concentration gradient

– Transport proteins move solute molecules across the membrane

Solute binding Phosphorylation Transport Protein reversion

ATPADP

P Proteinchanges shape

PPhosphatedetaches

P


Exocytosis & Endocytosis

1. A vesicle may fuse with the membrane and expel its contents outside the cell (exocytosis)

2. Membranes may fold inward, enclosing material from the outside (endocytosis)

copyright © 2005 pearson education, inc. publishing as benjamin cummings a tour of the cell

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