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Chapter 2
The Structure and Function
of Animal Cells

© 2019 McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom.
No reproduction or further distribution permitted without the prior written consent of McGraw-Hill Education.
 What Are Cells? 1

The simpler prokaryotic cells lack nuclei and other

membrane-bound organelles.
• There are two domains: Archaea and Eubacteria.

Eukaryotic cells are larger and have many

membrane-bound organelles.

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 What Are Cells? 2

• In the hierarchy of biological organization, the

cell is the fundamental unit of life (figure 2.1).
• Therefore, everything an animal does is
ultimately happening at the cellular level.

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 What Are Cells? 3

There are three basic types of cells:

• Prokaryotic cells: bacteria and archaea.
• Eukaryotic.

All eukaryotes have three basic parts:

• Plasma membrane.
• Cytoplasm.
• Nucleus.

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 Figure 2.1 A Generalized Animal Cell

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 Cell Membranes 1

Cell membranes, composed mainly of

phospholipids and proteins, allow certain material
to move across them.
• This quality is called selective permeability.
• The fluid-mosaic model is based on knowledge of the
plasma membrane.

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 Cell Membranes 2

Cell membranes:
• Regulate movement of material.
• Separate the inside of the cell from the outside.
• Separate various organelles within the cell.
• Provide a large surface area.
• Are a site for receptors.
• Separate cells from one another.

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 Figure 2.3 Structure of the Plasma
Membrane

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 Figure 2.4 The Arrangement of Cholesterol
between Lipid Molecules of a Lipid Bilayer

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 Movement Across Membranes

Some molecules use their own energy to move.

• From an area of higher concentration to an area of
lower concentration.
• Examples include:
• Simple diffusion.
• Facilitated diffusion.
• Osmosis and filtration.

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 Figure 2.5 Diffusion through Membrane
Channels

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 Figure 2.9 Facilitated diffusion

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 Figure 2.6 Osmosis

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 Movement Across Cell Membranes
1

• The diffusion of water across a selectively

permeable membrane, from an area of higher
water concentration to an area of lower water
concentration, is osmosis.
• Osmosis is just a special type of diffusion, not a
different method.

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 Figure 2.7 Tonicity

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 Figure 2.8 Filtration

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 Movement Across Cell Membranes
2

Active transport across cell membranes requires

energy, from the cell, to move substances from
areas of lower concentration to areas of higher
concentration.
• This movement requires ATP.
• Three types of carrier proteins:
• Uniporters.
• Symporters.
• Antiporters.

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 Figure 2.10 Active Transport

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 How are metabolism and energy
related?
Metabolism = the sum of all cellular reactions
energy is the capacity to do work.
• Adenosine triphosphate (ATP) is the molecule that
makes energy available within all cells.
• Mitochondria are the organelles most responsible for
energy conversions.

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 An Overview of Energy Metabolism 1

Adenosine triphosphate (ATP) is the energy

currency of the cell.
• Comprised of a nitrogen-containing base (adenine), a
sugar (ribose), and three phosphate groups.

Bonds between phosphates are high energy bonds.

• Takes energy to form the bonds.
• Derived from foods animals eat.
• Energy is released when the bonds are broken.
• Used to drive cellular reactions.

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 Figure 2.11 The ATP Cycle

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 An Overview of Energy Metabolism 2

Cellular reactions occur in multistep, linked

metabolic pathways.
• Provides multiple intermediate compounds that can
serve as branch points for alternative pathways.
• Provides multiple points for control of the pathway.

Enzymes are catalysts that do not get incorporated into

the products of their reaction.
Enzymes combine with substrates in ways that stress
the substrates, lowering the energy required for the
reaction to occur.
• The energy of activation.
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 Glycolysis and Fermentation 1

The first set of reactions animals use to harvest

energy occurs in the cytoplasm.
• 10-step sequence, begins with glucose.

Each step is mediated by a specific enzyme.

Glucose is broken down into two, three-carbon
molecules called pyruvate.

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 Glycolysis and Fermentation 2

Initial steps require an expenditure of two ATPs.

• Four ATPs are produced for a net gain of two ATPs.

Two reduced coenzymes (NADH) are produced from

NAD.
• NADH carries energy to the mitochondria.

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 Glycolysis and Fermentation 3

If oxygen is absent (anaerobic conditions)

Pyruvate is metabolized using hydrogens from
NADH.
• Produces lactic acid.
• Called lactate fermentation.
• Supplies a very small amount of ATP.

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 The Mitochondrion and Aerobic
Respiration
When oxygen is present pyruvate and NADH enter the
mitochondria for further processing.
Mitochondrial processing involves two subset reaction
sequences.
• First subset is called the Krebs cycle.
• Oxidizes pyruvate to CO2 and results in additional ATP and
reduced coenzymes; occur in matrix.
• Second subset is called the electron transport system.
• Harvests energy within reduced coenzymes produced in
glycolysis and the Krebs cycle; occur across inner membrane.

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 Cytoplasm, Organelles, and Cellular
Components
Mitochondria convert energy in food molecules to
ATP, a form the cell can use.
• Because they produce energy, they can be called
“power generators.”
• Mitochondria also contain DNA.
• Mitochondria can multiply and increase their numbers
when energy demands increase.

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 Figure 2.14 Mitochondrion

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 Figure 2.16 The Electron Transport System
and Chemiosmosis

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 The Nucleus: Information Center
The nucleus.
• Contains DNA.
• Control and information center.
• Directs chemical reactions.
• Stores genetic information.
The nuclear envelope contains many pores that
allow material to enter and leave the nucleus.

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 Figure 2.17 The nuclear envelope

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 The Nucleus: Information Center 2

• The chromosomes in the nucleus have DNA

organized into genes which are specific DNA
sequences that control and regulate cell
activities.
• The nucleus is a preasembly point for
ribosomes.

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 Figure 2.18 Vaults

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 Vaults
Vaults – unknown function.
• Cytoplasmic ribonucleoproteins.
• Shaped like octagonal barrels.
• Plentiful, 1000s in 1 cell.
• Size and shape similar to nuclear pores.
• May act as a cellular ‘truck’ picking material (mRNA) up at the
nuclear pore and delivering it to ribosomes.

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 Endoplasmic Reticulum
The endoplasmic reticulum (ER):
• A series of channels that transports proteins.
• Also stores enzymes and proteins.
• A site of ribosome attachment (figure 2.15).

There are two types of ER:

• Smooth ER.
• Rough ER.

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 The Golgi Apparatus 1

• Named for Camillo Golgi, who discovered it in

1898.
• A collection of membranes associated
physically and functionally with the ER.
• Composed of flattened stacks of membrane-
bound cisternae.
• Sorts, packages, and secretes proteins and
lipids.

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 The Golgi Apparatus 2

Proteins that ribosomes synthesize are passed

into the ER and sealed off in little packets called
transfer vesicles.
Transfer vesicles pass from the ER to the Golgi
concentrates and chemically modifies proteins.
• Mark and sort the proteins into different batches for
different destinations.
• Eventually packaged into membrane-enclosed vesicles.
Most abundant in cells that secrete chemical
substances to the outside of the cell.
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 Figure 2.19 The Endomembrane
System

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 Vacuoles
Vacuoles.
• Membranous sacs.
• Part of endomembrane system.
• Varied functions in different cells.
• Collect and pump water.
• Storage of food.

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 Lysosomes
Membrane bound spherical organelles.
contain acid hydrolase enzymes that break down:
• Extracellular material.
• Waste intracellular organic molecules.
• Worn organelles.

Fuse with vesicles containing food or wastes or

engulf intracellular debris, allowing lysosomal
enzymes to digest the food, wastes, or debris.
Breakdown products used in energy processing or
recycled for anabolic functions.
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 Additional process for Movement
Across Cell Membranes
Additional process that move molecules across
membranes include:
• Endocytosis.
• Pinocytosis.
• Phagocytosis.
• Receptor-mediated endocytosis.
• Exocytosis.

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 Figure 2.20 Exocytosis and Endocytosis

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 Peroxisomes
Microbodies are membrane-enclosed vesicles that
contain a variety of enzymes.
One specific microbody is the peroxisome.
• Catalyze the removal of electrons and the associated
hydrogen atoms from hydrogen peroxide.
• Would otherwise disrupt metabolic pathways.
• Hydrogen peroxide is dangerous to cells:
• Violent chemical reactivity.
• Mediates cellular damage and aging.
• Broken down by catalase (within peroxisom.es).

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 The Cytoskeleton
Microtubules, intermediate filaments, and
microfilaments make up the cytoskeleton of the
cell.
• The cytoskeleton functions in transport, support, and
movement of structures in the cell such as organelles
and chromosomes.

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 Figure 2.21 The Cytoskeleton

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 Figure 2.22 Three Classes of Protein Fibers
Making Up the Cytoskeleton of Eukaryotic Cells

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 Cilia and Flagella
Cilia and flagella are appendages on the surface of
some cells and function in movement.
• Cilia may also act as a signal antenna for the cell.
• Flagella are larger than cilia.
• Both cilia and flagella are attached to a basal body.

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 Figure 2.23 The Structure of Cilia and
Flagella

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 Tissues
Groups of cells that have similar structure and
embryonic origin.
Perform a specialized function.
Animals may have up to four tissue types:
• Epithelial tissue.
• Connective tissue.
• Nervous tissue.
• Muscle tissue.

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No reproduction or further distribution permitted without the prior written consent of McGraw-Hill Education.