What is the difference between life and non-life? Where does the line begin?

All organisms are made of cells The cell is the simplest collection of matter

that can live Cell structure is correlated to cellular function

—The contraction of muscle cells allows you to move your eyes as you read this sentence.

All cells are related by their descent from earlier cells—however, they have been modified in many different ways throughout the history of life on Earth.

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Light Microscopes: visible light is passed through the specimen and then through glass lenses.

The lenses bend in the light in such a way that the image is magnified.

Magnification=the ratio of an object’s image size to its real size

Resolution=a measure of the clarity of the image

Light microscopes cannot resolve detail finer than 200 nm, the size of a small bacterium—that’s about 1,000 times the size of the object.

Advantage: Light Microscopes can observe living organisms

Pollen grain

Red Blood Cells

Electron Microscopes were first invented in the 1950s.

They focus a beam of electrons through a specimen or onto its surface.

They have a resolution 100 X better than a light microscope.

Disadvantage: Only nonliving material can be studied

Above: Spider shown with a Scanning Electron Microscope

10 m

1 m

0.1 m

1 cm

1 mm

100 µm

10 µm

1 µm

100 nm

10 nm

1 nm

0.1 nm Atoms

Small molecules

Lipids

Proteins

Ribosomes

Viruses

Smallest bacteria

Mitochondrion

Nucleus

Most bacteria

Most plant and animal cells

Frog egg

Chicken egg

Length of some nerve and muscle cells

Human height

Un

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eye

Lig

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mic

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Ele

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The Size Range of Cells:

Most cells are between 1 and 100 micrometers in diameter (see light region of chart to the right .

Note:The scale is logarithmic, each reference mark is a tenfold increase in size from the bottom to top

All cells have a plasma membrane surrounding the cytosol (a semifluid, jellylike substance in which organelles are found.

All cells contain chromosomes and ribosomes

Variations in other components, however, can be found between cells.

Prokaryotic cells are characterized by having No nucleus DNA in an unbound

region called the nucleoid

No membrane-bound organelles

“Pro”=before “karyo”=kernel/nucleus Bacteria are Prokaryotic

Eukaryotic cells have DNA enclosed by a membrane in the nucleus.

“Eu”= True In addition, they

have other membrane-bound organelles in the cytoplasm

Generally, they are much larger than prokaryotic cells

All organisms except bacteria have eukaryotic cells

Size is a general aspect of cell structure that relates to function

Limits to cell size are due to the logistics of carrying out cell functions

Having organelles to move materials around allows eukaryotic cells to be larger than prokaryotic cells.

Elephants don’t have larger cells than other organisms—they just have more cells!

The surface area to volume ratio of a cell is critical. As the surface area increases by a factor of n2, the volume increases by a factor of n3

Small cells have a greater surface area relative to volume

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Surface Area and Volume

Why is this important to cells?

Fig. 6-9a

ENDOPLASMIC RETICULUM (ER)

Smooth ER

Rough ERFlagellu

m

Centrosome

CYTOSKELETON:

MicrofilamentsIntermediate

filamentsMicrotubules

Microvilli

Peroxisome

Mitochondrion Lysosom

e

Golgiapparatus

Ribosomes

Plasma membrane

Nuclearenvelope

NucleolusChromatin

NUCLEUS

A Typical Animal Cell:

Fig. 6-9b

NUCLEUS

Nuclear envelopeNucleolusChromatin

Rough endoplasmic reticulum

Smooth endoplasmic reticulumRibosomes

Central vacuole

MicrofilamentsIntermediate filaments

Microtubules

CYTO-SKELETON

Chloroplast

PlasmodesmataWall of adjacent

cell

Cell wall

Plasma membrane

Peroxisome

Mitochondrion

Golgiapparatus

A Typical Plant Cell

Cells need to build proteins Cells need energy Cells need to make more cells

Proteins are macromolecules that are used by organisms for many different things:

Building cell structures Transporting nutrients such as oxygen Enzymes speed up chemical reactions Hormones regulate functions of systems Defensive proteins guard against infection Responsive proteins communicate with

other cells WOW! Lots of Work!

The nucleus contains most of the genes in the eukaryotic cell

It is generally the most conspicuous organelle in a eukaryotic cell

The Nuclear Envelope encloses the nucleus

Chromatin contains the DNA of the cell—it is organized into individual chromosomes.

The nuclear envelope is a double membrane. It is perforated with pore structures. An intricate protein structure called a pore complex surrounds each pore.

The Nucleus is like the “brain” of the cell—controlling most of the activities of the cell. How does it do this? By controlling what proteins are made.

Proteins are the workhorse molecules of the cell—they are made by ribosomes.

The nucleus contains the following organelles that are needed for protein synthesis:

Nucleolus—builds rRNA and Ribosomes

Chromosomes/Chromatin—contains strands of DNA

Nuclear Membrane—has pores to allow mRNA to leave nucleus and go to ribosomes

Ribosomes are particles made of ribosomal RNA and protein

Ribosomes carry out protein synthesis in two locations: In the cytosol (free

ribosomes) On the outside of the

endoplasmic reticulum or the nuclear envelope (bound ribosomes)

DNA Controls the production of proteins in a series of steps that begins in the nucleus and ends at ribosomes.

Remember: Proteins do the work of the cell.

DNA directs which proteins are made.

Ribosomes build the proteins.

Take in nutrients Take in oxygen Build cell structures Remove wastes Make ATP Cells use many organelles

to obtain, store, and release energy: plasma membrane, ER, Golgi Apparatus, Lysosomes, Mitochondria and Chloroplasts ATP

“Endo”=inside Consists of: Nuclear Envelope,

Endoplasmic Reticulum, Golgi Apparatus, Lysosomes, Vacuoles, and the Plasma Membrane

“Endo”=inside; “plasm”=liquid; “reticula”=intricate network

ER is an intricate network of membranes that start at the nuclear membrane and continue throughout the cell to the plasma membrane.

Smooth ER=no ribosomes attachedRough ER=ribosomes attached

Smooth ER: Makes lipids Metabolizes

carbohydrates Detoxifies poisons Stores calcium

Rough ER: Because ribosomes are

attached, many proteins are made here, especially glyco-proteins. (what are these?)

Distributes proteins in vesicles (little membrane-bound bundles of proteins)

Makes membranes for the cell

Golgi Apparatus is a complex of flattened sacs of membranes (called cisternae).

Function: Modifies products of the

ER Manufactures certain

macromolecules Sorts and packages

materials into transport vesicles

The Golgi is like the UPS store: It is the packaging and shipping center of the cell.

“lysis”=to split Lysosomes are sacs of

enzymes that can digest large molecules

These enzymes can digest proteins, fats, polysaccharides, and nucleic acids—basically anything that enters the cell!

They can even digest organelles in the cell

Lysosomes may be called the “Stomach” of the cell; or even “The Suicide Sac”

Some types of cell can engulf another cell by phagocytosis; this forms a food vacuole

A lysosome fuses with the food vacuole and digests the molecules

Autophagy: The lysosome can also digest damaged organelles

These enzymes work best at pH 5

The lysosome makes its own enzymes

The pH inside the lysosome stays at ph 5 because the transport proteins in the membrane pump in H+ ions.

These enzymes don’t work well in the pH of the rest of the cell. Why? (so it won’t digest the cell if it leaks)

White Blood Cells such as this one contain many lysosomes. They engulf bacteria and digest them.

Lysosome diseases are often fatal.

The enzymes in the lysosome may be defective…if so, when the lysosome takes in macromolecules, they may not get digested properly

Undigested material builds up and lysosome gets larger & larger, eventually disrupting cells and organs.

Tay-Sachs disease is a genetic disease that causes fat molecules to build up in the brain. Affected children usually die before age 3.

Lysosomes can be used to kill cells when they are supposed to be destroyed

Some cells have to die for proper development in an organism

Apoptosis= “auto-destruct” process; lysosomes break open & kill the cell. Why?

Tadpoles lose their tails as they mature

Fingers are fused in the human embryo

Vacuoles are membrane-bound organelles whose functions vary—but most are used for storage of needed materials

Food vacuoles: formed by phagocytosis, then store food to be broken down by lysosomes

The central vacuole of mature plant cells develops from smaller vacuoles that come from the ER and Golgi apparatus.

This organelle in plants stores proteins, sugars, ions and water. Some may contain pigments to give color to flowers.

They may contain poisonous substances that keep the plant from being eaten.

The membrane around the central vacuoles is called the tonoplast.

Protists are fresh-water single-celled organisms. They live in an environment that causes water to constantly diffuse into their body. This could cause swelling and death.

Contractile Vacuoles act like water pumps, continually pumping water out of the cell. Contractile Vacuoles in a

Paramecium

Mitochondria and Chloroplasts change energy from one form to another.

Mitochondria are the sites for cellular respiration; Chloroplasts are the sites for photosynthesis.

MitochondrionChloroplasts

Mitochondria –where cellular respiration occurs.

Where the chemical energy stored in sugars such as glucose is converted to ATP—a molecule that stores cellular energy.

The “Powerhouse” of the cell

Mitochondria have 2 membranes; the inner one is folded to increase the surface area. Enzymes attached to the membranes do the work of the mitochondria.

Almost all eukaryotic cells have mitochondria—either one very large mitochondrion, or thousands of smaller ones.

Which types of cells would have lots of mitochondria? Hint: Which cells need a lot of energy?

Chloroplasts, found in plants and algae are where photosynthesis occurs

They convert the energy from sunlight into organic compounds such as glucose.

“Little Green Sugar Factories”

Chloroplasts also have two membranes; the inner membranes form sacs that are stacked. In these membranes, chlorophyll (green pigment) traps sunlight energy.

Both transform energy from one kind to another

Both make ATP Both have double

membranes Both are semi-

autonomous organelles—they can move, change shape, and divide

Both have their own DNA and ribosomes—almost like independent cells-within-a-cell

A peroxisome is a specialized metabolic compartment.

Peroxisomes contain special enzymes that remove hydrogen from various substrates to form H2O2 (hydrogen peroxide).

This process may detoxify poisons, or break down fuel for energy.

Peroxisomes produce H2O2 as a by-product of many of the reactions in a cell.

H2O2 is toxic, so the peroxisome has an enzyme, catalase, that breaks down H2O2.

Organelles involved in organizing the cell so that it can divide are:

Cytoskeleton Centrioles (in

animal cells)

The cytoskeleton is a network of fibers that organizes structures and activities in the cell.

It gives the cell shape and support, much like the framework of a building holds it up and divides it into rooms.

Besides giving shape to the cell, the cytoskeleton anchors the other organelles.

It can be quickly dismantled in one part of the cell, then reassembled in a new location, changing the shape of the cell!

The cytoskeleton consists of three types of structures:Microtubules, Microfilaments, and Intermediate filaments

VesicleATP Receptor for

motor protein

Microtubuleof cytoskeleton

Motor protein (ATP powered)

MicrotubuleVesicles 0.25 µm

By interacting with motor proteins, the cytoskeleton can move whole cells or just move parts of the cell around. Inside the cell, vesicles can travel to their destinations along “monorails” provided by the cytoskeleton.

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

The cytoskeleton is composed of three main elements : 1.actin filaments (shown in red); also called microfilaments.2.mictrotubules (gold) 3. intermediate filaments (blue)

Hollow tubes made of Tubulin Function: maintains cell shape, cell

motility (as in cilia or flagella), chromosome movement in cell division, organelle movement.

CiliaFlagellum

Tiny thread-like fibers made of 2 intertwined strands of actin

Function: Maintains cell shape, changes in cell shape, muscle contraction, cytoplasmic streaming, cell motility (as in pseudopodia), and cell division (cleavage furrow formation)

Made of fibrous proteins supercoiled into thicker cables

Function: maintenance of cell shape, anchoring nucleus and certain organelles

In animal cells, microtubules grow out from a centrosome which is located near the nucleus.

Within the centrosome is a pair of centrioles, each made of 9 sets of triplet microtubules. Centrioles in

animal cells are essential for cell division.

They are not found in plant cells.

Cilia are hairlike extensions of certain cells that enable the cell to move or move fluid across the surface of the cell.

Flagellum are singular long, tail-like extensions that also enable certaincells to move.

Both cilia and flagella are made of microtubules.

The cell wall is found outside the plant cell.

Cell walls protect the plant cell, maintains its shape, and prevents excessive uptake of water.

Cell walls are made mostly of microfibrils of cellulose.

A young plant first secretes a relatively thin and flexible cell wall called the primary cell wall.

Between primary cell walls of adjacent cells is the middle lamela, a thin layer rich in sticky polysaccharides called pectin.

Some cells will add a secondary cell wall outside the primary cell wall. Wood is primarily secondary cell walls

Plant cellulose cell walls from the ragweed plant anther (Ambrosia psilostachya).

The rigid cell wall of plants is made of fibrils of cellulose embedded in a matrix of several other kinds of polymers such as pectin and lignin.

Although each cell appears encased within a box, in fact primary cell walls are perforated permitting plasmodesmata to connect adjacent cells.

Animal cells do not have cell walls, but they do have an elaborate extracellular matrix. The main ingredients are glycoproteins (the most abundant is collagen). Proteoglycans are

proteins with many carbohydrate chains attached.Integrins are proteins embedded in the cell membrane that attach to the extracellular matrix.The main functions of the ECM: adhesion, support, regulation