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Chapter 4Structure and

Function of Cells

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Cells Are the Basic Units of Life

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4.1 All organisms are composed of cells

The cell theory states A cell is the basic unit of life All living things are made up of cells New cells arise only from preexisting cells

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Figure 4.2A The sizes of living things and their components

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4.2 Metabolically active cells are small in size

Surface-area-to-volume ratio constrains increases in a cell’s size

Actively metabolizing cells need to be small Cells that specialize in absorption have

modifications to increase the surface-area-to-volume ratio

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Figure 4.2B Surface-area-to-volume relationships

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APPLYING THE CONCEPTS—HOW SCIENCE PROGRESSES

4.3 Microscopes allow us to see cells

Compound light microscope Multiple lenses increase magnifying power

A condenser lens focuses light through specimen An objective lens magnifies the specimen’s image An ocular lens magnifies the image into the eye

Electron microscope More magnifying power than light microscope

Transmission electron microscope passes electrons through specimen

Scanning electron microscope collects and focuses electrons scattered by the specimen

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Figure 4.3 Comparison of three microscopes

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4.4 Prokaryotic cells evolved first

Prokaryotic cells Lack a membrane-bound nucleus Smaller than eukaryotic cells Have a single chromosome, semifluid

cytoplasm, and thousands of ribosomes

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Figure 4.4B Prokaryotic cell structure

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Figure 4.4A Size comparison of a eukaryotic cell and a prokaryotic cell

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Archaea and Bacteria

Two domains of prokaryotic cells Different nucleic acid bases Bacteria cause many diseases, but are also

important in the environment for recycling nutrients

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4.5 Eukaryotic cells contain specialized organelles:

An overview Eukaryotic cells are third domain of cells Cytoskeleton - protein fibers that maintain cell

shape Have membrane-bound nucleus and organelles

Endomembrane system: endoplasmic reticulum, Golgi apparatus, and lysosomes

Energy-related organelles: mitochondria and chloroplasts

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Figure 4.5A Animal cell anatomy

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Figure 4.5B Plant cell anatomy

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Protein Synthesis Is a Major Function of Cells

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4.6 The nucleus contains the cell’s genetic information

Nucleus contains chromatin, a network of strands that condenses to form chromosomes Chromosomes contain DNA which carries

genes, the units of heredity Nucleolus - dark region of chromatin with

ribosomal RNA (rRNA) Nuclear envelope separates the nucleus

from the cytoplasm, but has nuclear pores to permit passage of ribosomal subunits

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Figure 4.6 Anatomy of the nucleus

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4.7 The ribosomes carry out protein synthesis

Ribosomes – non-membrane-bound particles where protein synthesis occurs

Endoplasmic reticulum (ER) – a membranous system where ribosomes attach and aid in protein synthesis

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Figure 4.7 Function of ribosomes

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4.8 The endoplasmic reticulum synthesizes and transports

proteins and lipids

The ER attaches to the nuclear envelope Rough ER is studded with ribosomes that

synthesize proteins Smooth ER lacks proteins and is where lipids

are made

Transport vesicles carry proteins and lipids to Golgi apparatus for modification

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Figure 4.8 Rough ER (RER) and smooth ER (SER)

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4.9 The Golgi apparatus modifies and repackages proteins

for distribution

One side is directed toward the ER and the other toward the cytoplasm

Golgi apparatus sorts and packages proteins and lipids in vesicles Vesicles are secreted from the cell membrane

via exocytosis

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Figure 4.9 Golgi apparatus (gray-green) and transport vesicles

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APPLYING THE CONCEPTS - HOW SCIENCE PROGRESSES

4.10 Pulse-labeling allows observation of the secretory pathway

George Palade pulse-labeled the rough ER with radioactive amino acids to observe the pathway of protein secretion

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Vesicles and Vacuoles Have Varied Functions

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4.11 Lysosomes digest macromolecules and cell parts

Lysosomes - membrane-bound vesicles produced by the Golgi apparatus Important in recycling cellular material and digesting worn-out

organelles Tay Sachs disease – when a particular lysosomal enzyme is

nonfunctional

Figure 4.11 Lysosome fusing with and destroying spent organelles

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4.12 Peroxisomes break down long-chain fatty acids

Peroxisomes - small, membrane-bound organelles resembling empty lysosomes

Contain enzymes to digest excess fatty acids Produces products used by mitochondria to

make ATP

Produce cholesterol and phospholipids found in brain and heart tissue

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4.13 Vacuoles have varied functions in protists and plants

Vacuoles – membranous sacs larger than vesicles and usually store substances Example: toxic substances used in plant defense

Central vacuole – found in plants, contains watery sap and maintains turgor pressure

Figure 4.13 Central vacuole of a plant cell

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4.14 The organelles of the endomembrane system

work together

Endomembrane system is a series of membranous organelles that work together and communicate via transport vesicles Includes: ER, Golgic apparatus, lysosomes and

transport vesicles

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Figure 4.14 The organelles of the endomembrane system

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A Cell Carries Out Energy Transformations

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4.15 Chloroplasts capture solar energy and produce carbohydrates

Chloroplasts - type of plastid, an organelle bounded by a double membrane with a series of internal membranes separated by a ground substance Endosymbiotic theory - from eukaryotic cell

engulfing a photosynthetic bacteria

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Figure 4.15 Chloroplast structure

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4.16 Mitochondria break down carbohydrates and produce ATP

Mitochondria were also derived from bacteria and therefore have a double membrane Often called the powerhouse of the cell

because they produce most of the ATP

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Figure 4.16 Mitochondrion structure

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APPLYING THE CONCEPTS—HOW BIOLOGY IMPACTS OUR LIVES

4.17 Malfunctioning mitochondria can cause human diseases

Mutations in mitochondrial DNA (mtDNA) have been linked to diseases Bi-products of ATP

formation can damage mtDNA

mtDNA mutations can be inherited

Example: Parkinsons or Alzheimer patients have more mtDNA mutations

Figure 4.17 Mitochondria within a muscle cell

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The Cytoskeleton Maintains Cell Shape and Assists Movement

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4.18 The cytoskeleton consists of filaments and microtubules

Actin filaments - long, thin flexible fibers in bundled or mesh-like networks Play a structure role in the plasma membrane Creates pseudopods amoebas to crawl

Actin filaments interact with motor molecules, proteins that attach, detach, and reattach causing movement

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Intermediate Filaments and Microtubules

Intermediate filaments - size between actin filaments and microtubules Support nuclear envelope or plasma membrane and

are in cell-to-cell junctions Microtubules – made of globular protein tubulin

Radiate from centrosome and maintain cell shape and create tracks along which organelles move

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Figure 4.18 The three types of protein components of the cytoskeleton

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4.19 Cilia and flagella contain microtubules

Cilia and flagella - whiplike structures of cells Unicellular protists use them to move In our bodies cilia remove debris from

respiratory tract and move eggs along oviduct

Grow from basal bodies - same structure as centrioles, structures located outside the nucleus and used in mitosis

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Figure 4.19 Flagellum

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In Multicellular Organisms, Cells Join Together

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4.20 Modifications of cell surfaces influence their behavior

Plants have a primary cell wall of cellulose microfibrils and a middle lamella of pectin Channels, plasmodesma, connect adjacent

cells allowing water and solutes through Animals cells have junctions between

plasma membranes Anchoring junctions prevent leakage Tight junctions seal in digestive justices Gap junctions allow cells to communicate

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Figure 4.20A Plant cells are joined by plasmodesmata

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Figure 4.20B Animal cells are joined by three different types of junctions

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Connecting the Concepts:Chapter 4

Eukaryotic cells contain several types of organelles.

But not all eukaryotic cells contain every type of organelle. Cells have many specializations of structure for their particular functions. Red blood cells lack a nucleus allowing more room for

molecules of hemoglobin, the molecule that transports oxygen in the blood

Muscle cells are tubular and specialized to contract Nerve cells have very long extensions that facilitate

the transmission of impulses