chapter 4 a tour of the cell. copyright © 2004 pearson education, inc. publishing as benjamin...

CHAPTER 4CHAPTER 4

A Tour of the Cell

Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings

• If you stacked up 8000 cell membranes, they would be only as thick as a page in this book

• Every second, your body produces about 2 million red blood cells


• An electron microscope can visualize objects a million times smaller than the head of a pin

• The cells of a whale are about the same size as the cells of a mouse


• Antibiotics are one of the great marvels of modern medicine

BIOLOGY AND SOCIETY: DRUGS THAT TARGET CELLS

– Treatment with these drugs will kill invading bacteria

– The drugs don’t harm the human cells of the host


• Cells are the building blocks of all life

THE MICROSCOPIC WORLD OF CELLS

• Cells must be tiny for materials to move in and out of them fast enough to meet the cell’s metabolic needs


• Organisms are either:

– Single-celled, such as most bacteria and protists

– Mult-icelled, such as plants, animals, and most fungi


• The light microscope is used by many scientists

Microscopes as Windows to Cells

– Light passes through the specimen

– Lenses enlarge, or magnify, the image

(a) Light micrograph (LM) of a white blood cell (stained purple) surrounded by red blood cells


• Magnification

– An increase in the specimen’s apparent size

• Resolving power

– The ability of an optical instrument to show two objects as separate


• Cells were first discovered in 1665 by Robert Hooke

• The accumulation of scientific evidence led to the cell theory

– All living things are composed of cells

– All cells form from previously existing cells


• The electron microscope (EM) uses a beam of electrons

– It has a higher resolving power than the light microscope


• The electron microscope can magnify up to 100,000X

– Such power reveals the diverse parts within a cell

Human height

Length of somenerve andmuscle cells

Frogeggs

Chickenegg

Plant andanimalcells

NucleusMost bacteriaMitochondrion

Smallest bacteria

Viruses

Ribosomes

Proteins

Lipids

Smallmolecules

AtomsU

na

ide

d e

ye

Lig

ht

mic

ros

co

pe

Ele

ctr

on

mic

ros

co

pe


SEM• The scanning electron

microscope (SEM) is used to study the detailed architecture of the surface of a cell

(b) Scanning electron micrograph (SEM) of cilia (above)And a white blood cell


TEM

• The transmission electron microscope (TEM) is useful for exploring the internal structure of a cell

(c) Transmission electron micrograph (TEM) of a white blood cell & cilial


• The countless cells on earth fall into two categories

The Two Major Categories of Cells

– Prokaryotic cells

– Eukaryotic cells


Cell Size is Limited• Surface to Volume Ratio limits upper size

• Larger cells have less surface area relative to volume


• Prokaryotic and eukaryotic cells differ in several respects

Prokaryotic cell Nucleoid region

Eukaryotic cell Nucleus Organelles


• Prokaryotic cells

– Are smaller than eukaryotic cells

– Lack internal structures surrounded by membranes

– Lack a nucleus


Prokaryoticflagella

Nucleoid region (DNA)

RibosomesPlasmamembrane

Cell wall

Capsule

Pili


A Generic Animal Cell


• An idealized plant cell


• Surrounded by a double membrane called the nuclear envelope

Structure and Function of the Nucleus

– It contains

– chromatin -a DNA-protein structure

– a nucleolus - which produces ribosomal parts

– Nucleoplasm

• Occurs only in eukaryotic cells


Nuclear Pore Complex

Allows movement of material into and out of nucleus


• Ribosomes build all the cell’s proteins

– Are not membrane bound

Ribosomes


• DNA controls the cell by transferring its coded information into RNA

How DNA Controls the Cell

– The information in the RNA is used to make proteins

Synthesis ofmRNA in thenucleus

1

2 Movement ofmRNA intocytoplasm vianuclear pore

3 Synthesis ofprotein in thecytoplasm

DNA

mRNA

Nucleus

Cytoplasm

mRNA

Ribosome

Protein


• Many of the membranous organelles in the cell belong to the endomembrane system

– Endoplasmic reticulum - rough and smooth

– Golgi Apparatus

– Lysosomes

– Vacuoles

THE ENDOMEMBRANE SYSTEM: MANUFACTURING AND DISTRIBUTING

CELLULAR PRODUCTS


• The endoplasmic reticulum (ER)

The Endoplasmic Reticulum

– Greek for ‘network within a cell’

– Produces an enormous variety of molecules

– Is composed of smooth and rough ER

Nuclearenvelope

Ribosomes

Rough ERSmooth ER


• The “roughness” of the rough ER is due to ribosomes that stud the outside of the ER membrane

Rough ER


• The functions of the rough ER include

– Producing proteins

– Producing new membrane


• After the rough ER synthesizes a molecule it packages the molecule into transport vesicles

1


Smooth ER• The smooth ER lacks

the surface ribosomes of ER

• Produces lipids, including steroids and sex hormones

• Regulates sugar

• Detoxifies drugs

• Stores calcium


• The Golgi apparatus

The Golgi Apparatus

– Works in partnership with the ER

– Refines, stores, and distributes the products of cells

Transportvesiclefrom ER

“Receiving” side ofGolgi apparatus

Golgi apparatus

New vesicle forming

Transport vesiclefrom the Golgi

“Shipping” side ofGolgi apparatus

Plasma membrane


• A lysosome is a membrane-enclosed sac

Lysosomes

– Greek for ‘breakdown body’

– It contains digestive enzymes

• Isolated by membrane

– The enzymes break down

• Macromolecules

• Old organelles


• Lysosomes have several types of digestive functions

• They exit the Golgi apparatus


– They fuse with food vacuoles to digest the food


– They fuse with old organelles to recycle parts

– Digest bacteria in white blood cells


Lysosomal diseasesGenetic disorders

Recipe is messed up

Enzyme doesn’t work

what should get broken down doesn’t

Tay-Sachs

lipids aren’t broken down

build up occurs

death by age 5

Pompe’s disease

glycogen builds up


• Vacuoles are membranous sacs

Vacuoles

– Two types are the contractile vacuoles of protists and the central vacuoles of plants

Figure 4.15

Contractilevacuoles

Centralvacuole

(a) Contractile vacuoles in a protist (b) Central vacuole in a plant cell


• A review of the endomembrane system


• Cells require a constant energy supply to do all the work of life

CHLOROPLASTS AND MITOCHONDRIA: ENERGY CONVERSION


• Chloroplasts are the sites of photosynthesis, the conversion of light energy to chemical energy

CHLOROPLASTS

Figure 4.17

Inner and outermembranes ofenvelope

Space betweenmembranes

Stroma (fluid inchloroplast)

Granum


Chloroplasts• Double membrane

• Grana

– Stacks of thylakoids

• Hollow disks

• Sunlight energy is coverted to chemical energy

• Stroma- fluid filling chloroplast

• Contains some DNA


• Mitochondria are the sites of cellular respiration, which involves the production of ATP from food molecules

Mitochondria

Figure 4.18

Outermembrane

Innermembrane

Cristae

Matrix

Space betweenmembranes


Mitochondria• Double membrane

– Big bag stuffed into smaller bag

– Folds of inner bag called cristae

• Matrix -space inside inner bag

• Contains some DNA


• The cytoskeleton is an infrastructure of the cell consisting of a network of fibers

– Microfilaments - small threads

– Intermediate filaments - ropelike

– Microtubules - small tubes

THE CYTOSKELETON:CELL SHAPE AND MOVEMENT


• One function of the cytoskeleton

Maintaining Cell Shape

– Provide mechanical support to the cell and maintain its shape


Figure4.9x


• The cytoskeleton can change the shape of a cell

– This allows cells like amoebae to move


• Cilia and flagella are motile appendages

Cilia and Flagella


• Flagella propel the cell in a whiplike motion

• Cilia move in a coordinated back-and-forth motion

Figure 4.20A, B


• Some cilia or flagella extend from nonmoving cells

– The human windpipe is lined with cilia

– Smoking damages the cilia


Cilia and Flagella

• Same structure and function

• 9 + 2 arrangement of microtubules

• Wrapped in plasma membrane


Mechanism of Movement• Dynein arms use ATP for energy to ‘walk’ up adjoining

microtubule, causing them to bend


• Most cells secrete materials that are external to the plasma membrane

• This extra cellular matrix

– Regulates

– Protects

– Supports

CELL SURFACES:PROTECTION, SUPPORT, AND CELL-CELL

INTERACTIONS


• Plant cells are encased by cell walls

Plant Cell Walls and Cell Junctions

Figure 4.21

– These provide support for the plant cells

Walls of two adjacentplant cells

Vacuole

Plasmodesmata(channels between cells)


• Animal cells lack cell walls

Animal Cell Surfaces and Cell Junctions

– They secrete a sticky covering called the extracellular matrix

– This layer helps hold cells together


• Animal cells connect by various types of junctions

– Tight junctions - leakproof

– Adhering junctions - hold cells together but allows movement between of materials between cells

– Communicating junctions - like plasmodesmata


Figure 4.22

Extracellular matrix

(a) Tight junctions

(b) Anchoring junctions

(c) Communicating junctions

Plasma membranesof adjacent cells

Extracellular matrix

chapter 4 a tour of the cell. copyright © 2004 pearson education, inc. publishing as benjamin...

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