Chapter 7

Cell Structure and Function

Ch 7-1 Life is Cellular

• Goals:• Explain the Cell Theory• Describe how researchers explore living cells• Distinguish between eukaryotes and

prokaryotes

Discovery of the Cell

• Cells- basic units of life• Robert Hooke (1665)- first to use the term cell while

looking at cork cells using compound microscope• Anton van Leeuwenhoek (1674) uses single lens

microscope to see microorganisms• Matthias Schleiden (1838) concludes all plants are

made of cells• Theodor Schwann (1839) concludes all animals are

made of cells• Rudolph Virchow (1855) proposes all cells come from

existing cells

Cell Theory

• These observations led to Cell Theory:– All living things are composed of cells– Cells are the basic unit of structure and function in

living things– All cells come from existing cells

Improved Cell Exploration

• Compound light microscope- magnify up to 1000x– Staining can improve visibility of organelles– Fluorescent staining may also be used

• Confocal light microscope- scans cells with laser beam to make 3-D images

• Electron microscopes- magnify up to 100,000x and resolve biological structures as small as 2 nanometers and– gave biologists the ability to see with great clarity the

structures that make up cells

Figure 4.1B10 m

1 m

100 mm(10 cm)

10 mm(1 cm)

1 mm

Human height

Length ofsome nerveand musclecells

Chickenegg

Frog egg

Human eggParamecium

100 m

10 m

1 m

100 nm

10 nm

Most plant andanimal cells

1 nm

0.1 nm

NucleusMost bacteria

Mitochondrion

Smallest bacteriaViruses

Ribosome

Proteins

Lipids

Small molecules

Atoms

Un

aid

ed e

ye

Lig

ht

mic

rosc

op

e

Ele

ctro

n m

icro

sco

pe

Figure 4.1B_2

1 mmFrog egg

Human eggParamecium

100 m

10 m

1 m

100 nm

10 nm

Most plant andanimal cells

1 nm

0.1 nm

NucleusMost bacteriaMitochondrion

Smallest bacteriaViruses

Ribosome

Proteins

Lipids

Small molecules

AtomsL

igh

t m

icro

sco

pe

Ele

ctro

n m

icro

sco

pe

Figure 4.1B_3

Types of Electron Microscopes

• Transmission electron microscopes (TEMs) pass a beam of electron through a thin specimen

• Scanning electron microscopes (SEMs) scan a beam of electrons over the surface of a specimen– Create excellent 3-D images

• Specimens from electron microscopy are viewed in a vacuum, are preserved and dehydrated, so living cells cannot be viewed

New Microscope Technology

• Scanning probe microscopes- trace surface of specimens with fine probe while electronically recording the position

Prokaryotes and Eukaryotes

Prokaryotes• Cell membrane• DNA (coiled into a region

called the nucleoid)• Cytoplasm• Ribosomes• No true organelles• Generally smaller than

eukaryotes• Bacteria

Eukaryotes• Cell membrane• Nucleus (a membrane

surrounds the DNA)• Cytoplasm• Generally larger and more

complex– Contain dozens of structures

(including ribosomes) and internal membranes

• Highly specialized– Single celled protists, RBC, etc.

Figure 4.3

Fimbriae

Ribosomes

Nucleoid

Plasma membrane

Cell wall

Capsule

Flagella A TEM of the bacteriumBacillus coagulans

Bacterialchromosome

A typical rod-shapedbacterium

Ch 7-2 Eukaryotic Cell Structure

• Goals:– Describe the function of the nucleus– Describe the function of major cell organelles– Identify main roles of cytoskeleton

Eukaryotic Cell Structures

• The structures and organelles of eukaryotic cells can be organized by their basic functions

Smoothendoplasmicreticulum

Roughendoplasmicreticulum

NUCLEUS:NuclearenvelopeChromatinNucleolus

Ribosomes

Golgiapparatus

Mitochondrion

Plasma membrane

Peroxisome

CYTOSKELETON:Microtubule

Intermediatefilament

Microfilament

Lysosome

Centriole

NOT IN MOSTPLANT CELLS:

Figure 4.4B

NUCLEUS:Nuclear envelopeChromatinNucleolus

Golgiapparatus

Roughendoplasmicreticulum

Ribosomes

Peroxisome

Central vacuole

NOT IN ANIMAL CELLS:

ChloroplastCell wall

Plasmodesma

Mitochondrion

Plasma membrane

Cell wall ofadjacent cell

Smoothendoplasmicreticulum

CYTOSKELETON:MicrotubuleIntermediatefilamentMicrofilament

Cytoplasm

• Clear, gelatinous fluid inside of the cells– Organelles are suspended in this jelly-like matrix

Nucleus

• Central, membrane-bound organelle that contains DNA (in the form of chromatin) which controls cellular functions

• Contains directions to make proteins– Therefore controls activity of all other organelles

• Membrane is a porous, double-membrane referred to as the nuclear envelope

Chromatin (in nucleus)• Like a tangled ball of yarn in the nucleus• Becomes organized into chromosomes just

before a cell divides

Nucleolus

• Prominent organelle within the nucleus– Appears as a prominent dark area in the nucleus

• Assembly of ribosomes begins

Figure 4.5

Two membranesof nuclear envelope

Nucleus

Chromatin

Nucleolus

Pore

Endoplasmicreticulum

Ribosomes

Ribosomes (rRNA)

• Sites where the cell produces proteins according to directions of DNA

• Simple structure made of RNA and protein• Must leave the nucleus and enter cytoplasm

to make proteins– A DNA copy with instructions for making proteins

is sent to a ribosome in the cytoplasm or one attached to the ER

Figure 4.6

Ribosomes ERCytoplasm

Endoplasmicreticulum (ER)

Free ribosomes

Boundribosomes

Diagram ofa ribosome

ProteinmRNA

Colorized TEM showingER and ribosomes

Endoplasmic Reticulum (ER)

• Highly-folded membranes make up the ER– Allows for lots of surface area for chemical reactions to

take place– Fits into a compact space

• Rough ER has ribosomes imbedded in surface– Newly made proteins leave the ribosome and are

inserted into the ER where they are chemically modified• Smooth ER has no ribosomes

– Produces enzymes responsible for the synthesis of membrane lipids and detoxification of drugs (liver cells)

Smooth ER

Rough ER

Ribosomes

Nuclearenvelope

Transport vesiclebuds off

mRNA

Ribosome

Polypeptide

Glycoprotein

Rough ER

Sugarchain

Secretoryproteininside trans-port vesicle

4

3

2

1

Golgi Apparatus

• Made of a series of tubular membranes • Receives proteins synthesized on ribosomes of

the ER• Modifies the proteins• Then sorts and packs them into vesicles for

secretion or to be shipped to other parts of the cell

Lysosomes

• Contain digestive enzymes– Digest excess or worn out organelles, food

particles (lipids, carbohydrates, and proteins), engulfed viruses, or bacteria

• Membrane prevents enzymes from leaking out, but membrane can fuse with vacuole to digest its contents

• Lysosomes can ingest the cell itself

Digestiveenzymes

Lysosome

Plasma membrane

Digestiveenzymes

Lysosome

Food vacuole

Plasma membrane

Digestiveenzymes

Lysosome

Food vacuole

Plasma membrane

Digestiveenzymes

Lysosome

Food vacuole

Plasma membrane

Digestion

Lysosome

Vesicle containingdamaged mitochondrion

Lysosome

Vesicle containingdamaged mitochondrion

Lysosome

Vesicle containingdamaged mitochondrion

Digestion

Vacuoles• Vacuoles are large vesicles that have a variety of

functions.– Can store water, salts, proteins, and carbohydrates

• Large, central vacuole in plants gives plant turgor pressure

– Some protists have contractile vacuoles that help to eliminate water

– In plants, vacuoles may• have digestive functions,• contain pigments, or• contain poisons that protect the plant.

Contractilevacuole

Nucleus

Central vacuole

Chloroplast

Nucleus

Mitochondria

• Mitochondria are organelles that carry out cellular respiration in nearly all eukaryotic cells.

• Cellular respiration converts the chemical energy in foods to chemical energy in ATP (adenosine triphosphate).

Mitochondria

• Mitochondria have two internal compartments.1. The intermembrane space is the narrow region

between the inner and outer membranes.2. The mitochondrial matrix contains

• the mitochondrial DNA,• ribosomes, and• many enzymes that catalyze some of the reactions of

cellular respiration.

Matrix

Cristae

Innermembrane

Outermembrane

Mitochondrion

Intermembranespace

Chloroplasts

• Chloroplasts are the photosynthesizing organelles of all photosynthesizing eukaryotes.

• Photosynthesis is the conversion of light energy from the sun to the chemical energy of sugar molecules (glucose).

Chloroplasts

• Chloroplasts are partitioned into compartments.– Between the outer and inner membrane is a thin

intermembrane space.– Inside the inner membrane is

• a thick fluid called stroma that contains the chloroplast DNA, ribosomes, and many enzymes and

• a network of interconnected sacs called thylakoids.• In some regions, thylakoids are stacked like poker chips.

Each stack is called a granum, where green chlorophyll molecules trap solar energy.

Figure 4.14

Inner andoutermembranes

Granum Stroma Chloroplast

Thylakoid

EVOLUTION CONNECTION: Mitochondria and chloroplasts evolved by endosymbiosis

• Mitochondria and chloroplasts have– DNA and– ribosomes.

• The structure of this DNA and these ribosomes is very similar to that found in prokaryotic cells.

• The endosymbiont theory proposes that– mitochondria and chloroplasts were formerly small

prokaryotes and– they began living within larger cells.– Idea first suggested by biologist Lynn Margulis

Mitochondrion Nucleus

Endoplasmicreticulum

Engulfing ofphotosyntheticprokaryote

Chloroplast

Host cell

Mitochondrion

Host cell

Engulfingof oxygen-using prokaryote

Somecells

Benefits of Membrane-bound Organelles

• Separates cell functions into distinct compartments– Allows chemical reactions to occur simultaneously

Cytoskeleton

• Network of tiny rods and filaments within the cytoplasm that provides support and structure for the cell

• Help anchor and support organelles• Involved in movement• Microtubules- thin hollow cylinders made of

protein• Microfilaments- smaller, solid protein fibers

made of actin

Cytoskeleton

• Cells contain a network of protein fibers, called the cytoskeleton, which functions in structural support and motility.

• Scientists believe that motility and cellular regulation result when the cytoskeleton interacts with proteins called motor proteins.

Cytoskeleton

• The cytoskeleton is composed of three kinds of fibers.1. Microfilaments (actin filaments) support the cell’s

shape and are involved in motility.2. Intermediate filaments reinforce cell shape and

anchor organelles.3. Microtubules (made of tubulin) give the cell rigidity

and act as tracks for organelle movement.

Actin subunit

Nucleus

Nucleus

Microfilament Intermediate filament

Fibrous subunits

7 nm 10 nm

Tubulin subunits

Microtubule

25 nm

Cilia and flagella move when microtubules bend

• While some protists have flagella and cilia that are important in locomotion, some cells of multicellular organisms have them for different reasons.– Cells that sweep mucus out of our lungs have cilia.– Animal sperm are flagellated.

Outer microtubule doublet

Centralmicrotubules

Radial spoke

Dynein proteins

Plasma membrane

Centrioles

• Play an important role in cell division• Found in cells of animals and most protists

Ch 7-2 Cell Boundaries

• Goals:• Identify the main functions of the cell

membrane and cell wall• Describe what happens during diffusion• Explain the processes of osmosis, facilitated

diffusion, and active transport

Cell Wall

• Fairly rigid structure located outside the plasma membrane in some cells– Plants, fungi, bacteria, and some protists

• Provides support and protection• Composed of cellulose• Very porous, so it is NOT selectively

permeable– That is the job of the cell membrane

Cell Membrane

• Flexible phospholipid bilayer with proteins responsible for maintaining homeostasis

• Surrounds all cellsOutsideof cell

Insideof cell(cytoplasm)

Cellmembrane

Proteins

Proteinchannel

phospholipid bilayer

Carbohydratechains

Cell Membrane

• Maintains homeostasis by:• Regulating what enters and leaves the cell • Also provides protection and support• Composed of a double-layered sheet called

the lipid bilayer which includes– embedded and attached proteins in a structure

biologists call a fluid mosaic

Cell Membrane

• Fluid Mosaic Model– Fluid: in motion -Mosaic: “pattern” of

phospholipids and proteins on cell surface

Outsideof cell

Insideof cell(cytoplasm)

Cellmembrane

Proteins

Proteinchannel

phospholipid bilayer

Carbohydratechains

http://telstar.ote.cmu.edu/Hughes/tutorial/cellmembranes/bil.swf

Cell Membrane

• Many phospholipids are made from unsaturated fatty acids that have kinks in their tails.

• These kinks prevent phospholipids from packing tightly together, keeping them in liquid form.

• In animal cell membranes, cholesterol helps stabilize the membranes– prevent the fatty acid tails from sticking together

Cell Membranes

• Membranes may exhibit selective permeability, allowing some substances to cross more easily than others.

• Brownian motion- random movement of atoms and molecules – caused by their collisions with one another

• Diffusion is the net movement of molecules across a concentration gradient – Move from an area of high concentration to and area of

low concentration– http://www.biosci.ohiou.edu/introbioslab/Bios170/diffusi

on/Diffusion.html– Slow process because it relies on random motion of atoms

and molecules• Diffusion does not require energy so it is referred to

as passive transport• Eventually, the particles reach equilibrium where the

concentration of particles is the same throughout

Diffusion

Figure 5.3A

Molecules of dye Membrane

Pores

Net diffusion Net diffusion Dynamic Equilibrium

Osmosis• Diffusion of water across a membrane

Osmosis

• High concentration of water to low concentration of water

• Fresh water to salt water• http://www.stolaf.edu/people/giannini/flasha

nimat/transport/osmosis.swf

Hypotonic Solution• ‘Hypo-’ means less• Concentration of solute

(dissolved solids) is less outside of cell than inside

• Therefore a higher concentration of water outside the cell

• Water will enter cell• Cell may lyse (burst)• Cell wall prevents lysis in

plant cells

Hypertonic Solution• ‘Hyper-’ means more• Concentration of solute

is higher outside of cell• Therefore a lower

concentration of water outside the cell

• Water leaves the cell• Results in plasmolysis in

plant cells

Isotonic Solution

• ‘Iso-’ means equal• Solute concentration is

the same outside and inside the cell

• Water moves in and out of the cell but in equal amounts

• No change in cell size• Animals prefer this

When molecules don’t diffuse

• Some molecules diffuse easily• Others do not because of their size, shape, or

polarity

Phospholipids

• Fatty acid tails are non-polar

• Heads are polar• Tails don’t want to be

near water because water is polar

• Polar Polar♥

• Non-polar ≠ Polar

Proteins

• Transport Proteins- needed for the movement of certain substances and waste materials across the plasma membrane

• Channel or carrier

Facilitated Diffusion

• Hydrophobic substances easily diffuse across a cell membrane.

• However, polar or charged substances do not easily cross cell membranes and, instead, move across membranes with the help of specific transport proteins

• Process is called facilitated diffusion, which– does not require energy and– relies on the concentration gradient.

Active Transport

• Requires energy (ATP)• Used for large molecules or substances

moving against their concentration gradient (low to high)

Endocytosis and Exocytosis

• Endocytosis- taking materials into the cell by means of infolding of membrane to form a vacuole

• 2 types:– phagocytosis- cytoplasmic

extensions surround food particle and package it in a vacuole

• Cell then engulfs it

– pinocytosis- formation of tiny pockets in cell membrane to take in liquids

Endocytosis and Exocytosis

• Exocytosis- membrane of a vacuole fuses with cell membrane and releases contents out of cell

Fibers ofextracellularmatrix (ECM)

Enzymatic activity

Phospholipid

Cholesterol

CYTOPLASM

CYTOPLASM

Cell-cellrecognition

Glycoprotein

Intercellularjunctions

Microfilamentsof cytoskeleton

ATPTransport

Signaltransduction

Receptor

Signalingmolecule

Attachment to the cytoskeletonand extracellular matrix (ECM)

Functions of Membrane Proteins

Other Protein Functions

• Other proteins– serve as tags on the surface to ID chemical signals

and other cells – On inner surface help anchor membrane to cell’s

internal support structure