Cell Structure and Function

Chapter 4 Part 2

4.7 Visual Summary of Eukaryotic Cells

Fig. 4-15a, p. 63

CELL WALL Protects, structurally

supports cell

CHLOROPLAST Specializes in

photosynthesis

CENTRAL VACUOLE Increases cell surface area; stores metabolic wastes

NUCLEUSnuclear envelope

Keeps DNA separated from cytoplasm; makes ribosome subunits; controls access to DNA

DNA in nucleoplasmCYTOSKELETON microtubules

Structurally supports, imparts

shape to cell; moves cell and its components

microfilaments RIBOSOMESintermediate filaments (not shown)

(attached to rough ER and free in cytoplasm) Sites of protein synthesis

ROUGH ERMITOCHONDRION Modifies proteins made by

ribosomes attached to itEnergy powerhouse; produces many ATP

by aerobic respiration SMOOTH ER

PLASMODESMACommunication

junction between adjoining cells

Makes lipids, breaks down carbohydrates and fats, inactivates toxins

GOLGI BODY Finishes, sorts, ships lipids, enzymes, and membrane and secreted proteins

LYSOSOME-LIKE VESICLEDigests, recycles materials

a Typical plant cell components.

PLASMA MEMBRANE Selectively controls the kinds and

amounts of substances moving into and out of cell; helps maintain

cytoplasmic volume, composition

nucleolus

4.7 Visual Summary of Eukaryotic Cells

Fig. 4-15b, p. 63

NUCLEUS

Keeps DNA

separated from

cytoplasm; makes

ribosome subunits;

controls access to

DNA

nuclear

envelope

nucleolus

DNA in

nucleoplasm

CYTOSKELETON

microtubules

Structurally

supports,

imparts shape

to cell; moves

cell and its

components

microfilaments RIBOSOMES

(attached to rough ER

and free in cytoplasm)

Sites of protein synthesis

intermediate

filaments

ROUGH ER Modifies

proteins made by

ribosomes attached to it

MITOCHONDRION

Energy powerhouse;

produces many ATP

by aerobic respiration

SMOOTH ER

Makes lipids, breaks

down carbohydrates and

fats, inactivates toxins

CENTRIOLES

Special centers that

produce and organize

microtubules

GOLGI BODYPLASMA MEMBRANE

Selectively controls the

kinds and amounts of

substances moving into

and out of cell; helps

maintain cytoplasmic

volume, composition

Finishes, sorts, ships

lipids, enzymes, and

membrane and

secreted proteins

LYSOSOME

Digests, recycles

materials

Animation: Common eukaryotic

organelles

4.8 The Nucleus

The nucleus keeps eukaryotic DNA away from

potentially damaging reactions in the cytoplasm

The nuclear envelope controls when DNA is

accessed

The Nuclear Envelope

Nuclear envelope

• Two lipid bilayers pressed together as a single

membrane surrounding the nucleus

• Outer bilayer is continuous with the ER

• Nuclear pores allow certain substances to pass

through the membrane

The Nucleoplasm and Nucleolus

Nucleoplasm

• Viscous fluid inside the nuclear envelope, similar

to cytoplasm

Nucleolus

• A dense region in the nucleus where subunits of

ribosomes are assembled from proteins and RNA

The Chromosomes

Chromatin

• All DNA and its associated proteins in the nucleus

Chromosome

• A single DNA molecule with its attached proteins

• During cell division, chromosomes condense and

become visible in micrographs

• Human body cells have 46 chromosomes

Chromosome Condensation

p. 65

one chromosome

(one unduplicated

DNA molecule)

one chromosome

(one duplicated DNA

molecule, partially

condensed)

one chromosome

(one duplicated DNA

molecule, completely

condensed)

4.9 The Endomembrane System

Endomembrane system

• A series of interacting organelles between the

nucleus and the plasma membrane

• Makes lipids, enzymes, and proteins for secretion

or insertion into cell membranes

• Other specialized cell functions

The Endoplasmic Reticulum

Endoplasmic reticulum (ER)

• An extension of the nuclear envelope that forms a

continuous, folded compartment

Two kinds of endoplasmic reticulum

• Rough ER (with ribosomes) folds polypeptides

into their tertiary form

• Smooth ER (no ribosomes) makes lipids, breaks

down carbohydrates and lipids, detoxifies poisons

Vesicles

Vesicles

• Small, membrane-enclosed saclike organelles

that store or transport substances

Peroxisomes

• Vesicles containing enzymes that break down

hydrogen peroxide, alcohol, and other toxins

Vacuoles

• Vesicles for waste disposal

Golgi Bodies and Lysosomes

Golgi body

• A folded membrane containing enzymes that

finish polypeptides and lipids delivered by the ER

• Packages finished products in vesicles that carry

them to the plasma membrane or to lysosomes

Lysosomes

• Vesicles containing enzymes that fuse with

vacuoles and digest waste materials

The Endomembrane System

The Endomembrane System

The Endomembrane System

Fig. 4-18a, p. 66

nucleus

rough ER

smooth ER

Golgi body

vesicles

Fig. 4-18b, p. 66

protein

RNA

C Vesicles

Vesicles that bud from the

rough ER carry some of

the new proteins to Golgi

bodies. Other proteins

migrate through the

interior of the rough ER,

and end up in the smooth

ER.

ribosome attached to ER

vesicle budding from ER

B Rough ER

Some of the RNA in

the cytoplasm is

translated into

polypeptide chains

by ribosomes

attached to the

rough ER. The

chains enter the

rough ER, where

they are modified

into final form.

A Nucleus

Inside the nucleus, DNA instructions

for making proteins are transcribed

into RNA, which moves through

nuclear pores into the cytoplasm.

Fig. 4-18c, p. 67

D Smooth ER

Some proteins

from the rough

ER are packaged

into new vesicles

and shipped to

the Golgi. Others

become enzymes

of the ER, which

assemble lipids or

inactivate toxins.

E Golgi body

Proteins

arriving in

vesicles from

the ER are

modified into

final form and

sorted. New

vesicles carry

them to the

plasma

membrane

or to

lysosomes.

F Plasma membrane

Golgi vesicles fuse with

the plasma membrane.

Lipids and proteins of a

vesicle’s membrane fuse

with the plasma

membrane, and the

vesicle’s contents are

released to the exterior

of the cell.

protein in smooth ER

Animation: The endomembrane system

4.10 Lysosome Malfunction

When lysosomes do not work properly, some

cellular materials are not properly recycled,

which can have devastating results

Different kinds of molecules are broken down by

different lysosomal enzymes

• One lysosomal enzyme breaks down

gangliosides, a kind of lipid

Tay Sachs Disease

In Tay Sachs disease, a genetic mutation alters

the lysosomal enzyme that breaks down

gangliosides, which accumulate in nerve cells

• Affected children usually die by age five

4.11 Other Organelles

Eukaryotic cells make most of their ATP in

mitochondria

Plastids function in storage and photosynthesis

in plants and some types of algae

Mitochondria

Mitochondrion

• Eukaryotic organelle that makes the energy

molecule ATP through aerobic respiration

• Contains two membranes, forming inner and

outer compartments; buildup of hydrogen ions in

the outer compartment drives ATP synthesis

• Has its own DNA and ribosomes

• Resembles bacteria; may have evolved through

endosymbiosis

Mitochondrion

Fig. 4-20, p. 69

outer membrane

outer

compartment

inner membrane

inner compartment

0.5 µm

Plastids

Plastids

• Organelles that function in photosynthesis or

storage in plants and algae; includes

chromoplasts, amyloplasts, and chloroplasts

Chloroplasts

• Plastids specialized for photosynthesis

• Resemble photosynthetic bacteria; may have

evolved by endosymbiosis

The Chloroplast

Fig. 4-21, p. 69

two outer

membranes

stroma

thylakoids

(inner membrane

system folded into

flattened disks)

Animation: Structure of a chloroplast

The Central Vacuole

Central vacuole

• A plant organelle that occupies 50 to 90 percent

of a cell’s interior

• Stores amino acids, sugars, ions, wastes, toxins

• Fluid pressure keeps plant cells firm

4.12 Cell Surface Specializations

A wall or other protective covering often

intervenes between a cell’s plasma membrane

and the surroundings

Eukaryotic Cell Walls

Animal cells do not have walls, but plant cells and many protist and fungal cells do

Primary cell wall

• A thin, pliable wall formed by secretion of cellulose into the coating around young plant cells

Secondary cell wall

• A strong wall composed of lignin, formed in some plant stems and roots after maturity

Plant Cell Walls

Fig. 4-22a, p. 70

Fig. 4-22a, p. 70

middle

lamella

plasma

membraneA Plant cell secretions

form the middle lamella,

a layer that cements

adjoining cells together.

cytoplasm

primary

cell wall

Fig. 4-22b, p. 70

Fig. 4-22b, p. 70

B In many plant tissues, cells

also secrete materials that are

deposited in layers on the inner

surface of their primary wall.

These layers strengthen the

wall and maintain its shape.

They remain after the

cells die, and become

part of pipelines

that carry water

through the

plant.

secondary

cell wall

(added in

layers)

primary

cell wall

pipeline

made of

abutting

cell walls

Fig. 4-22c, p. 70

Fig. 4-22c, p. 70

middle lamella

C Plasmodesmata are

channels across the cell

walls and the plasma

membranes of living cells

that are pressed against

one another in tissues.

plasmodesma

middle lamella

middle lamella

C Plasmodesmata are

channels across the

cell walls and the

plasma membranes

of living cells that are

pressed against one

another in tissues.

Fig. 4-22, p. 70

middle

lamella

plasma

membrane

A Plant cell secretions form the middle lamella, a layer that cements adjoining cells together.

cytoplasm

primary

cell wall

pipeline

made of

abutting

cell walls

plasmodesma

middle lamella

B In many plant

tissues, cells also

secrete materials that

are deposited in

layers on the inner

surface of their

primary wall. These

layers strengthen the

wall and maintain its

shape. They remain

after the cells die, and

become part of

pipelines that carry

water through the

plant.secondary

cell wall

(added in

layers)

primary

cell wall

Stepped Art

Animation: Plant cell walls

Plant Cuticle

Cuticle

• A waxy covering that protects exposed surfaces

and limits water loss

Fig. 4-23, p. 71

thick, waxy

cuticle at

leaf surface

cell of leaf

epidermis

photosynthetic

cell inside leaf

Matrixes Between Animal Cells

Extracellular matrix (ECM)

• A nonliving, complex mixture of fibrous proteins

and polysaccharides secreted by and surrounding

cells; structure and function varies with the type

of tissue

• Example: Bone is mostly ECM, composed of

collagen (fibrous protein) and hardened by

mineral deposits

ECM

A bone cell surrounded by extracellular matrix

Cell Junctions

Cell junctions allow cells to interact with each

other and the environment

In plants, plasmodesmata extend through cell

walls to connect the cytoplasm of two cells

Animals have three types of cell junctions: tight

junctions, adhering junctions, gap junctions

Cell Junctions in Animal Tissues

Fig. 4-25, p. 71

free surface of

epithelial tissue

different kinds of

tight junctions

gap junction

basement membrane

(extracellular matrix)

adhering junction

Animation: Animal cell junctions

4.6-4.12 Key Concepts:

Eukaryotic Cells

Cells of protists, plants, fungi, and animals are

eukaryotic; they have a nucleus and other

membrane-enclosed compartments

They differ in internal parts and surface

specializations

4.13 The Dynamic Cytoskeleton

Eukaryotic cells have an extensive and dynamic

internal framework called a cytoskeleton

Cytoskeleton

• An interconnected system of many protein

filaments – some permanent, some temporary

• Parts of the cytoskeleton reinforce, organize, and

move cell structures, or even a whole cell

Components of the Cytoskeleton

Microtubules

• Long, hollow cylinders made of tubulin

• Form dynamic scaffolding for cell processes

Microfilaments

• Consist mainly of the globular protein actin

• Make up the cell cortex

Intermediate filaments

• Maintain cell and tissue structures

Components of the

Cytoskeleton

Fig. 4-26 (a-c), p. 72

Fig. 4-26a, p. 72

Fig. 4-26a, p. 72

tubulin subunit

25 nm

Microtubule

Fig. 4-26b, p. 72

Fig. 4-26b, p. 72

actin subunit

6–7 nm

Microfilament

Fig. 4-26c, p. 72

one

polypeptide

chain

Intermediate filament

Fig. 4-26d, p. 72

Fig. 4-26, p. 72

one

polypeptide

chain

Intermediate filament

actin

subunit

6–7 nm

Microfilament

tubulin

subunit

25 nm

Microtubule

Stepped Art

Motor Proteins

Motor proteins

• Accessory proteins that move molecules through

cells on tracks of microtubules and microfilaments

• Energized by ATP

• Example: kinesins

Motor Proteins: Kinesin

Animation: Motor proteins

Cilia, Flagella, and False Feet

Eukaryotic flagella and cilia

• Whiplike structures formed from microtubules

organized into 9 + 2 arrays

• Grow from a centriole which remains in the

cytoplasm as a basal body

Psueudopods

• “False feet” used by amoebas and other

eukaryotic cells to move or engulf prey

Moving Cells

Flagellum of the human sperm, and pseudopods

of a predatory amoeba

Fig. 4-28a, p. 73

Fig. 4-28b, p. 73

Eukaryotic Flagella

and Cilia

Fig. 4-29a, p. 73

Fig. 4-29a, p. 73

protein

spokes

pair of microtubules

in a central sheath

pair of

microtubules

plasma

membrane dynein arms A Sketch and micrograph of one

eukaryotic flagellum, cross-section.

Like a cilium, it contains a 9+2 array:

a ring of nine pairs of microtubules

plus one pair at its core. Stabilizing

spokes and linking elements that

connect to the microtubules keep

them aligned in this radial pattern.

Fig. 4-29b, p. 73

Fig. 4-29b, p. 73

B Projecting from each pair

of microtubules in the outer

ring are “arms” of dynein, a

motor protein that has

ATPase activity. Phosphate-

group transfers from ATP

cause the dynein arms to

repeatedly bind the adjacent

pair of microtubules, bend,

and then disengage. The

dynein arms “walk” along the

microtubules. Their motion

causes adjacent microtubule

pairs to slide past one

another

basal body, a microtubule

organizing center that

gives rise to the 9+2 array

and then remains beneath

it, inside the cytoplasm

Fig. 4-29c, p. 73

Fig. 4-29c, p. 73

C Short, sliding strokes occur in a

coordinated sequence around the

ring, down the length of each

microtubule pair. The flagellum

bends as the array inside bends:

Animation: Flagella structure

4.13 Key Concepts:

A Look at the Cytoskeleton

Diverse protein filaments reinforce a cell’s shape

and keep its parts organized

As some filaments lengthen and shorten, they

move cell structures or the whole cell

Summary: Components of

Prokaryotic and Eukaryotic Cells

Animation: Nuclear envelope

Video: E. coli in food

Video: Cilia and flagella protozoans