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Chapter 3: Cell Structure and Function

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The cell theory states:

1. All organisms are composed of one or more cells.

2. Cells are the basic unit of structure and function in organisms.

3. All cells come only from other cells.

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Eukaryotic Cells

Eukaryotic cells have a nucleus that controls the workings of the cell.

All cells are surrounded by a plasma membrane made of phospholipids and proteins.

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The plasma membrane regulates what enters and exits the cell.

Inside the plasma membrane, the nucleus is surrounded by cytoplasm.

Plant cells have a cell wall in addition to the plasma membrane.

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Structure of the NucleusChromatin: DNA and proteinsNucleolus: Chromatin and ribosomal

subunitsNuclear envelope: Double membrane

with poresNucleoplasm: semifluid medium inside

the nucleus.

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Nucleus and nuclear envelope

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RibosomesProtein synthesis occurs at tiny

organelles called ribosomes.Ribosomes are composed of a large

subunit and a small subunit.Ribosomes can be found alone in

the cytoplasm, in groups called polyribosomes, or attached to the endoplasmic reticulum.

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The Endomembrane SystemThe endomembrane system consists of:

Nuclear envelopeEndoplasmic reticulum

Golgi apparatusVesicles

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The endoplasmic reticulumThe endoplasmic reticulum (ER) is a

system of membranous channels and saccules.

Rough ER is studded with ribosomes and is the site of protein synthesis and processing.

Smooth ER lacks ribosomes and is the site of synthesis of phospholipids and the packaging of proteins into vesicles, among other functions.

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The endoplasmic reticulum

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The Golgi apparatusThe Golgi apparatus consists of a

stack of curved saccules.The Golgi apparatus receives protein

and also lipid-filled vesicles from the ER, packages, processes, and distributes them within the cell.

This organelle may also be involved in secretion.

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The Golgi apparatus

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Lysosomes and vacuolesLysosomes are vesicles produced by the

Golgi apparatus.Lysosomes contain hydrolytic enzymes

and are involved in intracellular digestion.

Vacuoles (large) and vesicles (small) are membranous sacs in the cell that store substances.

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PeroxisomesPeroxisomes are vesicles than contain

enzymes.

The enzymes in these organelles use up oxygen and produce hydrogen peroxide.

Peroxisomes are abundant in the liver where they produce bile salts and cholesterol and break down fats.

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Energy-Related Organelles

The two energy-related organelles of eukaryotes are chloroplasts and mitochondria.

Both organelles house energy in the form of ATP.

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ChloroplastsA chloroplast is bounded by two

membranes enclosing a fluid-filled stroma that contains enzymes.

Membranes inside the stroma are organized into thylakoids that house chlorophyll.

Chlorophyll absorbs solar energy and carbohydrates are made in the stroma.

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Chloroplast structure

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Mitochondria

Mitochondria are found in plant and animal cells.

Mitochondria are bounded by a double membrane surrounding fluid-filled matrix.

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The inner membranes of mitochondria are cristae.

The matrix contains enzymes that break down carbohydrates and the cristae house protein complexes that produce ATP.

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Mitochondrion structure

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The CytoskeletonThe eukaryotic cytoskeleton is a network of

filaments and tubules that extends from the nucleus to the plasma membrane.

The cytoskeleton contains three types of elements responsible for cell shape, movement within the cell, and movement of the cell:

Actin filamentsMicrotubules

Intermediate filaments

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Actin filaments occur in bundles or mesh-like networks.

Actin filaments play a structural role in intestinal microvilli and also interact with motor molecules, such as myosin.

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Actin filaments

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Microtubles are small hollow cylinders made of the globular protein tubulin.

Microtubule assembly is controlled by the microtubule organizing center, called the centrosome.

Microtubules help maintain the shape of the cell and act as tracks along which organelles can move.

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Microtubule structure

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Intermediate filaments are ropelike assemblies of fibrous polypeptides that support the plasma membrane and nuclear envelope.

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Structure of intermediate filaments

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CentriolesCentrioles are short cylinders with

a 9 + 0 pattern of microtubule triplets.

Centrioles may be involved in microtubule formation and disassembly during cell division and in the organization of cilia and flagella.

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Centriole structure

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Cilia and flagellaCilia (small and numerous) and flagella

(large and single) have a 9 + 2 pattern of microtubules and are involved in cell movement.

Cilia and flagella move when the microtubule doublets slide past one another.

Each cilium and flagellum has a basal body at its base.

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Structure of a flagellum or cilium

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Evolution of the eukaryotic cell