Chapter 4 A View of the Cell

Cell History The microscope was invented in the 17th century Using a microscope, Robert Hooke discovered cells in 1665 All living things are made of cells (cell theory)

Cell Theory All cells come from preexisting cells The cell is the basic unit of organization of organisms. All organisms are made up of one or more cells.

The light microscope enables us to see the overall shape and structure of a cell Image seen by viewer Eyepiece Ocular lens Objective lens Specimen Condenser lens Light source

Electron microscopes were invented in the 1950s They use a beam of electrons instead of light The greater resolving power of electron microscopes –allows greater magnification –reveals cellular details

Scanning electron microscope (SEM) Scanning electron micrograph of cilia

Transmission electron microscope (TEM) Transmission electron micrograph of cilia

Below is a list of the most common units of length biologists use (metric) Cell sizes vary with their function

Cell size and shape relate to function

Cell Types There are two kinds of cells: prokaryotic and eukaryotic Prokaryotic cells are small, relatively simple cells –They do not have a nucleus

A prokaryotic cell is enclosed by a plasma membrane and is usually encased in a rigid cell wall –The cell wall may be covered by a sticky capsule Ribosomes Capsule Cell wall Plasma membrane Prokaryotic flagella Nucleoid region (DNA) Pili –Inside the cell are its DNA and other parts

All other life forms are made up of one or more eukaryotic cells These are larger and more complex than prokaryotic cells Eukaryotes are distinguished by the presence of a true nucleus Eukaryotic cells are partitioned into functional compartments

An animal cell Plasma membrane Golgi apparatus Ribosomes Nucleus Smooth endoplasmic reticulum Rough endoplasmic reticulum Mitochondrion Not in most plant cells Cytoskeleton Flagellum Lysosome Centriole Peroxisome Microtubule Intermediate filament Microfilament

The plasma membrane controls the cell’s contact with the environment The cytoplasm contains organelles Many organelles have membranes as boundaries –These compartmentalize the interior of the cell –This allows the cell to carry out a variety of activities simultaneously

A plant cell has some structures that an animal cell lacks: –Chloroplasts –A rigid cell wall

Nucleus Golgi apparatus Not in animal cells Central vacuole Chloroplast Cell wall Mitochondrion Peroxisome Plasma membrane Rough endoplasmic reticulum Ribosomes Smooth endoplasmic reticulum Cytoskeleton Microtubule Intermediate filament Microfilament

The largest organelle is usually the nucleus The nucleus is separated from the cytoplasm by the nuclear envelope The nucleus is the cellular control center –It contains the DNA that directs the cell’s activities The nucleus is the cell’s genetic control center

Chromatin Nucleolus Pore NUCLEUS Two membranes of nuclear envelope ROUGH ENDOPLASMIC RETICULUM Ribosomes

The endomembrane system is a collection of membranous organelles –These organelles manufacture and distribute cell products –The endomembrane system divides the cell into compartments –Endoplasmic reticulum (ER) is part of the endomembrane system

The rough ER manufactures membranes Ribosomes on its surface produce proteins Rough endoplasmic reticulum makes membrane and proteins Transport vesicle buds off Ribosome Sugar chain Glycoprotein Secretory (glyco-) protein inside transport vesicle ROUGH ER Polypeptide

Smooth ER synthesizes lipids In some cells, it regulates carbohydrate metabolism and breaks down toxins and drugs

SMOOTH ER ROUGH ER Nuclear envelope Ribosomes SMOOTH ERROUGH ER

The Golgi apparatus consists of stacks of membranous sacs –These receive and modify ER products, then send them on to other organelles or to the cell membrane

The Golgi apparatus Golgi apparatus “Receiving” side of Golgi apparatus Transport vesicle from ER New vesicle forming Transport vesicle from the Golgi Golgi apparatus “Shipping” side of Golgi apparatus

Lysosomes are sacs of digestive enzymes budded off the Golgi Lysosomes digest the cell’s food and wastes LYSOSOME Nucleus

Lysosomal enzymes –digest food –destroy bacteria –recycle damaged organelles –function in embryonic development in animals

Rough ER Transport vesicle (containing inactive hydrolytic enzymes) Golgi apparatus Plasma membrane LYSOSOMES “Food” Engulfment of particle Food vacuole Digestion Lysosome engulfing damaged organelle

Plant cells contain a large central vacuole –The vacuole has lysosomal and storage functions Central vacuole Nucleus

Protists may have contractile vacuoles Nucleus Contractile vacuoles –These pump out excess water

Chloroplasts are found in plants and some protists Chloroplasts convert solar energy to chemical energy in sugars ENERGY-CONVERTING ORGANELLES Chloroplast Stroma Inner and outer membranes Granum Intermembrane space

–This process uses the chemical energy in food to make ATP for cellular work Outer membrane MITOCHONDRION Intermembrane space Inner membrane Cristae Matrix Mitochondria carry out cellular respiration

A network of protein fibers makes up the cytoskeleton The cell’s internal skeleton helps organize its structure and activities THE CYTOSKELETON AND RELATED STRUCTURES

Microfilaments of actin enable cells to change shape and move Intermediate filaments reinforce the cell and anchor certain organelles Microtubules –give the cell rigidity –provide anchors for organelles –act as tracks for organelle movement