How Cells Are Put Together

Chapter 3

Cell Theory

• Every organism is composed of one

or more cells

• Cell is smallest unit with properties of

life

• Continuity of life arises from growth

and division of single cells

• Smallest unit of life

• Is highly organized for metabolism

• Senses and responds to environment

• Has potential to reproduce

Cell

Structure of Cells

All start out life with:– Plasma membrane – Region where DNA

is stored– Cytoplasm

Two types:– Prokaryotic– Eukaryotic

Overview of cells

Common eukaryotic organelles

Fig. 3-4, p.41

Most Cells Are Really Small

Surface-to-Volume Ratio

• Bigger cell, less surface area per unit

volume

• Above a certain size, material cannot

move in or out of cell fast enough

0.5 1.0 1.5

0.79

0.06

3.14 7.07

0.52 1.77

diameter (cm):

surface area (cm2):

volume (cm3):

surface- to-volume ratio: 13.17:1 6.04:1 3.99:1

Fig. 3-5, p.41

• Create detailed images of something that is too small to see

• Light microscopes– Simple or compound

• Electron microscopes– Transmission EM or Scanning EM

Microscopes

Limitations of Light Microscopy

• Cells must be thin enough for light to pass through

• Structures are usually stained

• Light microscopes can see details 200 nm in size

Electron Microscopy

• Uses beams of electrons rather than light

• Electrons are focused by magnets rather than glass lenses

• Can resolve structures down to 0.5 nm

Fig. 3-2a, p.40

Microscopes

Structure of Cell Membranes

• Fluid mosaic model

• Mixed composition:– Phospholipid bilayer – Glycolipids– Sterols– Proteins

Fig. 3-6b, p.42

one layer of lipids

one layer of lipids

Phospholipids

Lipid bilayer organization

Membrane Proteins

Adhesion proteins

Communication proteins

Receptor proteins

Recognition proteins

Passive transporters

Active transporters

Cell membranes

• Archaebacteria and eubacteria

• DNA is not enclosed in nucleus

• Generally the smallest, simplest cells

Prokaryotic Cells

Typical prokaryotic cell

Eukaryotic Cells

• Have a nucleus and other organelles

• Eukaryotic organisms– Plants– Animals– Protistans– Fungi

Eukaryotic Cell Features

• Plasma membrane• Nucleus• Endoplasmic

reticulum• Golgi body• Vesicles• Mitochondria• Ribosomes• Cytoskeleton

Table. 3-1, p.45

• Keeps the DNA molecules separated from metabolic machinery of cytoplasm

• Makes it easier to organize DNA and to copy it

The Nucleus

Components:Nuclear envelope NucleoplasmChromatin Nucleolus

The Nucleus

Fig. 3-9a, p.46

DNA in nucleus

rough ER

smooth ER

Golgi body

chromatin nucleolusnuclear envelope(two lipid bilayers)

cytoplasm

pore

the cell nucleus

RNA messages

The Nucleus

• Related organelles where lipids are assembled and new polypeptide chains modified

• Sorts and ships products to various destinations

• Consists of endoplasmic reticulum, Golgi bodies, vesicles

Endomembrane System

The endomembrane system

Endoplasmic Reticulum

• Starts at nuclear membrane and

extends throughout cytoplasm

• Rough ER: ribosome covered,

processes proteins

• Smooth ER: no ribosomes, builds lipids

Fig. 3-9d, p.46

smooth ER channel, cross-section

smooth ER

Endoplasmic Reticulum

Golgi Body

• Puts finishing touches on proteins and

lipids that arrive from ER

• Packages finished material for shipment to

final destinations

• Material arrives and leaves in vesicles

Fig. 3-9e-f, p.46

budding vesicle

Golgi body

plasma membrane

Secretory pathway ends.

Endocytic pathway begins.

Golgi Body

Vesicles

• Membranous sacs that

move through cytoplasm

• Lysosomes

• Peroxisomes

• ATP-producing powerhouses

• Membranes form two distinct

compartments

• ATP-making machinery embedded

in inner mitochondrial membrane

Mitochondria

Fig. 3-10, p.48

outer membrane

outer compartment

inner compartment

inner membrane

Chloroplasts

• Convert sunlight energy to ATP through photosynthesis

• Found in plants and some protistans

Fig. 3-11, p.48

two outermembranes

thylakoids(inner membranesystem folded intoflattened disks)

Organelle Origins

• Nucleus and ER– Infolding of membranes formed

compartments

• Mitochondria and chloroplasts– Endosymbiosis

Fig. 3-14d, p.50

flagellum

mitochondrionnucleus

chloroplast

Fig. 3-15a, p.51

DNA

infolding of plasma membrane

Infolding Bacterial Membranes

• Present in all eukaryotic cells

• Cell shape and internal organization

• Allows organelle movement within cells and, in some cases, cell motility

Cytoskeleton

Microtubules

• Largest elements

• Composed of tubulin

• Involved in shape, motility,

cell division

tubulinsubunit

Microfilaments

• Thinnest elements

• Composed of actin

• Take part in movement,

formation, and

maintenance of cell

shape

actinsubunit

Intermediate Filaments

• Only in animal cells of certain tissues

• Most stable cytoskeletal elements

• Helpful in determining tissue types

onepolypeptidechain

Cilia, Flagellum, and Psuedopod

Plant Cell Walls

Plant Vs Animal

Table. 3-2, p.57