Cell Structure and Function
Cell Structure and Function
Impacts, Issues:Food For Thought
A strain of E. coli bacteria that causes severe illness or death occasionally contaminates foods such as ground beef and fresh vegetables
4.1 The Cell Theory
The cell theory, a foundation of modern biology, states that cells are the fundamental units of life
Measuring Cells
One micrometer (μm) is one-thousandth of a millimeter
Animalcules and Beasties
Van Leeuwenhoek was the first to describe small organisms seen through a microscope, which he called animalcules and beasties
Hooke was the first to sketch and name cells
Development of the Microscope
The Cell Theory Emerges
In 1839, Schleiden and Schwann proposed the basic concepts of the modern cell theory• All organisms consists of one or more cells• A cell is the smallest unit with the properties of life• Each new cell arises from division of another,
preexisting cell• Each cell passes its hereditary material to its
offspring
4.2 What Is a Cell?
Cell• The smallest unit that shows the properties of life
All cells have a plasma membrane and cytoplasm, and all start out life with DNA
The Basics of Cell Structure
Eukaryotic cell• Cell interior is divided into functional
compartments, including a nucleus
Prokaryotic cell• Small, simple cells without a nucleus
All Cells Have Three Things In Common
Plasma membrane• Controls substances passing in and out of the cell
DNA containing region• Nucleus in eukaryotic cells• Nucleoid region in prokaryotic cells
Cytoplasm• A semifluid mixture containing cell components
Prokaryotic and Eukaryotic Cells
Fig. 4-4a, p. 56
Fig. 4-4b, p. 56
Cells Have Large Surface Area-to-Volume Ratio
Cell Size
Surface-to-volume ratio restricts cell size by limiting transport of nutrients and wastes
Preview of Cell Membranes
Lipid bilayer• A double layer of phospholipids organized with
their hydrophilic heads outwards and their hydrophobic tails inwards
• Many types of proteins embedded or attached to the bilayer carry out membrane functions
Basic Structure of Cell Membranes
Fig. 4-6a, p. 57
hydrophilic head
two hydrophobic tails
A A phospholipid, the main type of lipid in cell membranes.
Fig. 4-6b, p. 57
Fig. 4-6c, p. 57
4.1-4.2 Key Concepts:What All Cells Have In Common
Each cell has a plasma membrane, a boundary between its interior and the outside environment
The interior consist of cytoplasm and an innermost region of DNA
4.3 How Do We See Cells?
We use different types of microscopes to study different aspects of organisms, from the smallest to the largest
Modern Microscopes
Light microscopes• Phase-contrast microscopes • Reflected light microscopes• Fluorescence microscopes
Electron microscopes• Transmission electron microscopes• Scanning electron microscopes
Light and Electron Microscopes
Fig. 4-7a, p. 58
Fig. 4-7b, p. 58
Fig. 4-8, p. 59
a) Light micrograph. A phase-contrast micro-scope yields high-contrast images of transparent specimens, such as cells.
b) Light micrograph. A reflected light micro-scope captures light reflected from opaque specimens.
c) Fluorescence micro-graph. The chlorophyll molecules in these cells emitted red light (they fluoresced) naturally.
d) A transmission electron micrograph reveals fantastically detailed images of internal structures.
e) A scanning electron micro-graph shows surface details of cells and structures. Often, SEMs are artificially colored to highlight certain details.
Stepped Art
Different Microscopes, Different Characteristics
4.3 Key Concepts:Microscopes
Microscopic analysis supports three generalizations of the cell theory: • Each organism consists of one or more cells and
their products • A cell has a capacity for independent life • Each new cell is descended from a living cell
4.4 Introducing Prokaryotic Cells
Bacteria and archaea are the prokaryotes (“before the nucleus”), the smallest and most metabolically diverse forms of life
Bacteria and archaea are similar in appearance and size, but differ in structure and metabolism
General Prokaryote Body Plan
Cell wall surrounds the plasma membrane• Made of peptidoglycan (in bacteria) or proteins (in
archaea) and coated with a sticky capsule
Flagellum for motion
Pili help cells move across surfaces• Sex pilus aids in sexual reproduction
Fig. 4-10, p. 60
flagellum
capsulecell wallplasma membrane
cytoplasm, with ribosomesDNA in nucleoid
pilus
Archaeans
Bacteria
4.5 Microbial Mobs
Although prokaryotes are all single-celled, few live alone
Biofilm• Single-celled organisms sharing a secreted layer
of polysaccharides and glycoproteins• May include bacteria, algae, fungi, protists, and
archaeans
A Biofilm
4.4-4.5 Key Concepts:Prokaryotic Cells
Archaeans and bacteria are prokaryotic cells, which have few, if any, internal membrane-enclosed compartments
In general, they are the smallest and structurally the simplest cells
4.6 Introducing Eukaryotic Cells
Eukaryotic (“true nucleus”) cells carry out much of their metabolism inside membrane-enclosed organelles
Organelle• A structure that carries out a specialized function
within a cell
Organelles of Eukaryotic Cells
Eukaryotes: Animal and Plant Cells
Fig. 4-14a, p. 62
vacuole
plasma membrane
mitochondrion
nucleus
1 µm(a) Human white blood cell.
Fig. 4-14b, p. 62
cell wall
central vacuole
plasma membrane
chloroplast
mitochondrion
nucleus
1 µm
(b) Photosynthetic cell from a blade of timothy grass.
4.7 Visual Summary of Eukaryotic Cells
4.7 Visual Summary of Eukaryotic Cells
4.8 The Nucleus
• The nucleus keeps eukaryotic DNA away from potentially damaging reactions in the cytoplasm
• The nuclear envelope controls when DNA is accessed
The Nuclear Envelope
• Nuclear envelope– Two lipid bilayers pressed together as a single
membrane surrounding the nucleus– Outer bilayer is continuous with the ER– Nuclear pores allow certain substances to
pass through the membrane
The Nucleoplasm and Nucleolus
• Nucleoplasm– Viscous fluid inside the nuclear envelope,
similar to cytoplasm
• Nucleolus– A dense region in the nucleus where subunits
of ribosomes are assembled from proteins and RNA
The Chromosomes
• Chromatin– All DNA and its associated proteins in the nucleus
• Chromosome– A single DNA molecule with its attached proteins– During cell division, chromosomes condense and
become visible in micrographs– Human body cells have 46 chromosomes
Chromosome Condensation
4.9 The Endomembrane System
• Endomembrane system– A series of interacting organelles between the
nucleus and the plasma membrane– Makes lipids, enzymes, and proteins for
secretion or insertion into cell membranes– Other specialized cell functions
The Endoplasmic Reticulum
• Endoplasmic reticulum (ER) – An extension of the nuclear envelope that forms a
continuous, folded compartment
• Two kinds of endoplasmic reticulum– Rough ER (with ribosomes) folds polypeptides into
their tertiary form– Smooth ER (no ribosomes) makes lipids, breaks
down carbohydrates and lipids, detoxifies poisons
Vesicles
• Vesicles– Small, membrane-enclosed saclike organelles
that store or transport substances
• Peroxisomes– Vesicles containing enzymes that break down
hydrogen peroxide, alcohol, and other toxins
• Vacuoles– Vesicles for waste disposal
Golgi Bodies and Lysosomes
• Golgi body– A folded membrane containing enzymes that finish
polypeptides and lipids delivered by the ER– Packages finished products in vesicles that carry
them to the plasma membrane or to lysosomes
• Lysosomes– Vesicles containing enzymes that fuse with vacuoles
and digest waste materials
The Endomembrane System
The Endomembrane System
The Endomembrane System
4.10 Lysosome Malfunction
• When lysosomes do not work properly, some cellular materials are not properly recycled, which can have devastating results
• Different kinds of molecules are broken down by different lysosomal enzymes– One lysosomal enzyme breaks down
gangliosides, a kind of lipid
Tay Sachs Disease
• In Tay Sachs disease, a genetic mutation alters the lysosomal enzyme that breaks down gangliosides, which accumulate in nerve cells– Affected children
usually die by age five
4.11 Other Organelles
• Eukaryotic cells make most of their ATP in mitochondria
• Plastids function in storage and photosynthesis in plants and some types of algae
Mitochondria
• Mitochondrion– Eukaryotic organelle that makes the energy molecule
ATP through aerobic respiration– Contains two membranes, forming inner and outer
compartments; buildup of hydrogen ions in the outer compartment drives ATP synthesis
– Has its own DNA and ribosomes– Resembles bacteria; may have evolved through
endosymbiosis
Mitochondrion
Plastids
• Plastids– Organelles that function in photosynthesis or
storage in plants and algae; includes chromoplasts, amyloplasts, and chloroplasts
• Chloroplasts– Plastids specialized for photosynthesis– Resemble photosynthetic bacteria; may have
evolved by endosymbiosis
The Chloroplast
The Central Vacuole
• Central vacuole– A plant organelle that occupies 50 to 90
percent of a cell’s interior– Stores amino acids, sugars, ions, wastes,
toxins– Fluid pressure keeps plant cells firm
4.12 Cell Surface Specializations
• A wall or other protective covering often intervenes between a cell’s plasma membrane and the surroundings
Eukaryotic Cell Walls
• Animal cells do not have walls, but plant cells and many protist and fungal cells do
• Primary cell wall– A thin, pliable wall formed by secretion of cellulose
into the coating around young plant cells
• Secondary cell wall– A strong wall composed of lignin, formed in some
plant stems and roots after maturity
Plant Cell Walls
Fig. 4-22a, p. 70
Fig. 4-22b, p. 70
Fig. 4-22c, p. 70
Plant Cuticle
• Cuticle– A waxy covering that protects exposed
surfaces and limits water loss
Matrixes Between Animal Cells
• Extracellular matrix (ECM)– A nonliving, complex mixture of fibrous
proteins and polysaccharides secreted by and surrounding cells; structure and function varies with the type of tissue
– Example: Bone is mostly ECM, composed of collagen (fibrous protein) and hardened by mineral deposits
ECM
• A bone cell surrounded by extracellular matrix
Cell Junctions
• Cell junctions allow cells to interact with each other and the environment
• In plants, plasmodesmata extend through cell walls to connect the cytoplasm of two cells
• Animals have three types of cell junctions: tight junctions, adhering junctions, gap junctions
Cell Junctions in Animal Tissues
4.6-4.12 Key Concepts:
Eukaryotic Cells
• Cells of protists, plants, fungi, and animals are eukaryotic; they have a nucleus and other membrane-enclosed compartments
• They differ in internal parts and surface specializations
4.13 The Dynamic Cytoskeleton
• Eukaryotic cells have an extensive and dynamic internal framework called a cytoskeleton
• Cytoskeleton– An interconnected system of many protein filaments –
some permanent, some temporary– Parts of the cytoskeleton reinforce, organize, and
move cell structures, or even a whole cell
Components of the Cytoskeleton
• Microtubules– Long, hollow cylinders made of tubulin– Form dynamic scaffolding for cell processes
• Microfilaments– Consist mainly of the globular protein actin– Make up the cell cortex
• Intermediate filaments– Maintain cell and tissue structures
Fig. 4-26 (a-c), p. 72
Fig. 4-26d, p. 72
Motor Proteins
• Motor proteins– Accessory proteins that move molecules
through cells on tracks of microtubules and microfilaments
– Energized by ATP– Example: kinesins
Motor Proteins: Kinesin
Cilia, Flagella, and False Feet
• Eukaryotic flagella and cilia– Whiplike structures formed from microtubules
organized into 9 + 2 arrays– Grow from a centriole which remains in the
cytoplasm as a basal body
• Psueudopods– “False feet” used by amoebas and other
eukaryotic cells to move or engulf prey
Moving Cells• Flagellum of the human sperm, and pseudopods of a
predatory amoeba
Fig. 4-29a, p. 73
Eukaryotic Flagella and Cilia
Fig. 4-29b, p. 73
Fig. 4-29c, p. 73
4.13 Key Concepts:
A Look at the Cytoskeleton
• Diverse protein filaments reinforce a cell’s shape and keep its parts organized
• As some filaments lengthen and shorten, they move cell structures or the whole cell
Summary: Components of Prokaryotic and Eukaryotic
Cells