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Ch 3 – Cell Structure

Biology – Periods 2, 3, 4, & 6

Mrs. Stolipher

Cells Under the MicroscopeElectron microscopes have much higher magnifying and resolving powers

than light microscopes.

Chapter 3

• Cell size and

shape relate

to function

Figure 4.2

The Cell Theory

The Cell Theory has three parts:

1. All living things are made of one or more

cells.

2. Cells are the basic units of structure and

function in organisms.

3. All cells arise from existing cells.

Chapter 3

• At minimum, a cell must be large enough to house the

parts it needs to survive and reproduce

• The maximum size of a cell is limited by the amount of

surface needed to obtain nutrients from the

environment and dispose of wastes

Natural laws limit cell size

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Cell Size

Small cells function more efficiently than

large cells. If a cell’s surface area–to-volume

ratio is too low, substances cannot enter and

leave the cell well enough to meet the cell’s

needs.

• A small cell has a greater ratio of surface area

to volume than a large cell of the same shape

30 µm 10 µm

Surface area

of one large cube

= 5,400 µm2

Total surface

areaof 27 small

cubes

= 16,200 µm2

Figure 4.3

Common Cell Features

ALL Cells share common structural features, including:

• an outer boundary called the cell membrane,

• interior substance called cytoplasm,

• structural support called the cytoskeleton,

• genetic material in the form of DNA

• cellular structures that make proteins, called ribosomes

Prokaryotes

Prokaryotes are single-celled organisms that lack a nucleus and other internal compartments. They have a cell wall, may have cilia or flagella, and have a single circular molecule ofDNA.

Two Groups of Prokaryotes

• Early in the history of life, two different groups of prokaryotes evolved—eubacteria (which are commonly called bacteria) and archaebacteria.

• Eubacteria are prokaryotes that contain a chemical called peptidoglycan in their cell walls.

• Archaebacteria are prokaryotes that lack peptidoglycan in their cell walls and have unique lipids in their cell membranes.

Eukaryotic cells are partitioned into

functional compartments• All other life forms are made up of one or

more eukaryotic cells

• These are larger and more complex than

prokaryotic cells

• Eukaryotes are distinguished by the

presence of a true nucleus

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Eukaryotic Cells

Eukaryotic cells have:

• A nucleus which contains the cell’s DNA

• Other internal compartments called

organelles.

Comparing Prokaryotes and

Eukaryotes

Section 2 Cell FeaturesChapter 3

Watch video clip

Ch 3 – Sect 2 – vc10

Eukaryotic Cells

• The cytoskeleton provides the interior framework of a cell. There are three basic kinds of cytoskeletal fibers.

1. Microfilaments: long slender filaments made of the protein actin

2. Microtubules: hollow tubes made of the protein tubulin.

3. Intermediate fibers: thick ropes made of protein.

Eukaryotic Cells, continued

The cytoskeleton’s network of protein fibers anchors the cell’s organelles and other components of the cytoplasm.

The Cell Membrane

• The cell (plasma) membrane controls the cell’s contact with the environment

• The cell membrane is a selectively permeable barrier that determines which substances enter and leave the cell.

• The selective permeability of the cell is mainly caused by the way phospholipids interact with water.

• A phospholipid is a lipid made of a phosphate group and two fatty acids.

The Cell Membrane, continued

Cell membranes are made of a double layer of phospholipids, called a bilayer.

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The Cell Membrane, continuedThe Nucleus - cell’s genetic control

center

• Generally the largest organelle• The nucleus is an internal compartment that houses

the cell’s DNA. Most functions of a eukaryotic cell are controlled by the cell’s nucleus.

• is surrounded by a double membrane called the nuclear envelope, which separates the nucleus from the cytoplasm

• Scattered over the surface of the nuclear envelope are many small channels called nuclear pores.

The Nucleus, continued Nucleus of a CellSection 3 Cell OrganellesChapter 3

Overview: Many cell organelles are related through the

endomembrane system

• The endomembrane system is a collection

of membranous organelles

– These organelles manufacture and distribute

cell products

– The endomembrane system divides the cell

into compartments

– Endoplasmic reticulum (ER) is part of the

endomembrane system

Ribosomes and the Endoplasmic

Reticulum

• Ribosomes are the cellular structures on

which proteins are made.

• The Endoplasmic Reticulum or ER is an

extensive system of internal membranes that

move proteins and other substances through

the cell.

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Ribosomes and the Endoplasmic

Reticulum, continuedThe ER moves proteins and other substances within

eukaryotic cells.

Ribosomes and the Endoplasmic

Reticulum, continued

• The part of the ER with attached ribosomes is called the rough ER.

• The rough ER helps transport proteins that are made by the attached ribosomes.

• New proteins enter the ER.

• The portion of the ER that contains the completed protein pinches off to form a vesicle.

• A vesicle is a small, membrane-bound sac that transports substances in cells.

• The rough ER manufactures membranes

• Ribosomes on its surface produce proteins

12

3

4Transport

vesiclebuds off

Riboso

me

Sugarchain

Glycoprotein

protein

inside transport

vesicle

ROUGH

ERPolypept

ideFigure 4.8

Smooth endoplasmic reticulum has a

variety of functions

• Smooth ER synthesizes lipids

• In some cells, it regulates carbohydrate

metabolism and breaks down toxins and drugs

SMOOTH ER

ROUGHER

Nuclearenvelope

Ribosomes

SMOOTH ER ROUGH ER

Figure 4.9

Ribosomes and the Endoplasmic

Reticulum, continuedPackaging and Distribution of Proteins

• Vesicles that contain newly made proteins move through the cytoplasm from the ER to an organelle called the Golgi apparatus.

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The Golgi apparatus finishes, sorts, and

ships cell products

– The Golgi apparatus is a set of flattened, membrane-bound

sacs that serve as the packaging and distribution center of the

cell.

– These receive and modify ER products, then send them on to

other organelles or to the cell membrane

Golgi ApparatusSection 3 Cell OrganellesChapter 3

Lysosomes digest the cell’s food and

wastes

• Lysosomes are sacs of digestive enzymes budded off the Golgi

LYSOSOME

Nucleus• Lysosomal enzymes

–digest food

–destroy bacteria

– recycle damaged organelles

– function in embryonic

Figure 4.11B

Rough ER

Transport vesicle(containing inactivehydrolytic enzymes)

Golgiapparatus

Plasmamembrane

LYSOSOMES

“Food”

Engulfmentof particle

Foodvacuole

Digestion

Lysosomeengulfingdamagedorganelle

Connection: Abnormal lysosomes can

cause fatal diseases

• Lysosomal storage diseases are hereditary

– They interfere with other cellular functions

– Examples: Pompe’s disease - genetic disorder caused by a deficiency or

dysfunction of the lysosomal hydrolase which breaks down glycogen. The build-up of glycogen causes progressive muscle weakness throughout the body and affects various body tissues, particularly in the heart, skeletal muscles, liver and nervous system.

– Tay-Sachs disease - occurs when harmful quantities of a fatty acid derivative called a

ganglioside accumulate in the nerve cells of the brain. It is usually fatal.

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A review of the endomembrane system

• The various organelles of the

endomembrane system are interconnected

structurally and functionallyTransport vesiclefrom ER

Rough ER

Transport vesiclefrom Golgi

Plasmamembrane

Vacuole

LysosomeGolgi

apparatus

Nuclear

envelopeSmooth ER

Nucleus

Figure 4.14

Mitochondria

• Mitochondria are organelles that harvest

energy from organic compounds (food) to

make ATP.

• Mitochondria carry out cellular respiration

– This process uses the chemical energy in food to

make ATP for cellular work

• ATP is the main energy currency of cells. Most

ATP is made inside the mitochondria.

Mitochondria, continued

• Mitochondria have two membranes. The outer membrane is smooth. The inner membrane is greatly folded, and has a large surface area.

• Mitochondria have their own DNA. – They reproduce independently of the cell. – Mitochondrial DNA is similar to the DNA of

prokaryotic cells.

• Mitochondria are thought to be descendents of primitive prokaryotes.

Mitochondria, continued

Structures of Plant Cells

Plants have three unique structures that are not

found in animal cells:

• Cell Wall

• Chloroplasts

• Central Vacuole

Structures of Plant Cells – cell

wall• The cell membrane of plant cells is

surrounded by a thick cell wall, composed of proteins and carbohydrates.

• The cell wall

• helps support and maintain the shape of the cell

• protects the cell from damage

• connects the cell with adjacent cells

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Structures of Plant Cells -

chloroplasts• are organelles that use light energy to

make carbohydrates from carbon dioxide and water.

• along with mitochondria, supply much of the energy needed to power the activities of plant cells.

• like mitochondria, chloroplasts

– have their own DNA and reproduce independently of the plant cell.

– are thought to be descendents of ancient prokaryotes.

Structures of Plant Cell –

central vacuole

• Most of a plant cell’s volume is taken up by a large, membrane-bound space called the central vacuole.

• Functions in general maintenance of the cell• The central vacuole stores water and may

contain ions, nutrients, and wastes.• Protists (single celled eukaryotes) may have

contractile vacuoles– Which work to pump out excess water

Figure 4.5B

Nucleus

Golgiapparatus

Not inanimal

cells

Centralvacuole

Chloroplast

Cell wall

Mitochondrion

Plasma membrane

Roughendoplasmicreticulum

Ribosomes

Smoothendoplasmicreticulum

Cytoskeleton

Microtubule

Microfilament

An animal cell

Plasma membrane

Figure 4.5A

Golgiapparatus

Ribosomes

NucleusSmooth endoplasmicreticulum

Roughendoplasmicreticulum

Mitochondrion

Not in most plant cells

Cytoskeleton

Flagellum

Lysosome

Microtubule

Microfilament

Summary of Organelles