Cell Structure & Function

The History of the Cell Theory

• Before microscopes were invented, people believed that diseases were caused by curses and supernatural spirits.

• Microscopes enabled scientists to view and study cells, the basic units of living organisms.

• As scientists began using microscopes, they quickly realized they were entering a new world–one of microorganisms.

Early Contributions

●Robert Hooke - First person to see cells, he was

looking at cork and noted that he saw "a great many

boxes. (1665)

●Anton van Leeuwenhoek - Observed living cells in

pond water, which he called "animalcules" (1673)

A Compound Light microscope

(above)

The control center of an Electron

Microscope

Development of Microscopes

▪ Compound light microscopes use a series of lenses to magnify objects in steps.

These microscopes can magnify objects up to 1,500 times.

The electron microscope was invented in the 1940s.

This microscope uses a beam of electrons to magnify objects (cannot be alive)

Section 7.1 Summary – pages 171-174

• Robert Hooke was an English scientist who lived at the same time as van Leeuwenhoek.

The Cell Theory

• Hooke used a compound light microscope to study cork, the dead cells of cork bark.

• Along with Hooke & Leeuwenhoek, three other scientists help bring together the now famous cell theory.

Schleiden, Schwann, Virchow

●Theodore Schwann - zoologist who observed tissues of

animals had cells (1839)

●Mattias Schleiden - botanist, observed tissues of plants

contained cells ( 1845)

●Rudolf Virchow - also reported that every living thing is

made of up vital units, known as cells. He predicted that

cells come from other cells. (1850 )

Rudolf Virchow

The Cell Theory■ All living things are composed of one

or more cells.

■ Cells are basic units of structure and function in an organism.

■ Cells come only from pre-existing cells.

Cells are always small, how small depends on the type of cell

Cells can come in a variety of shapes

Cell size is also dependent on the surface area to volume ratio.

Figure 4.3

Prokaryote vs Eukaryote Cells

Endosymbiosis theory:

All organelles seem to share many properties with

bacteria. Lynn Margulis proposed endosymbiont

hypothesis: that organelles derived from ancient

colonization of large bacteria (became the eukaryotic cell)

by smaller bacteria (became the mitochondria, chloroplast,

etc.) Symbiosis = "living together".

*Mitochondria & Chloroplasts have their own DNA

• Cells that do not contain internal membrane-bound structures are called prokaryotic cells.

• The cells of most unicellular organisms such as bacteria do not have membrane bound structures and are therefore called prokaryotes.

Two Basic Cell TypesClick here

• Cells containing membrane-bound structures are called eukaryotic cells.

• Most of the multi-cellular plants and animals we know are made up of cells containing membrane-bound structures and are therefore called eukaryotes.

Click here

A prokaryotic cell does not have internal organelles surrounded by a membrane. Most of a prokaryote’s metabolism takes place in the cytoplasm.

1. Ribosomes

2. DNA 3. Plasma membrane

4. Cell wall

Click here to return to chapter summary

This eukaryotic cell from an animal has distinct membrane-bound organelles that allow different parts of the cell to perform different functions.

4. Plasma membrane

1. Nucleus

2. Nucleolus

3. Chromosomes

5. Organelles

Bacterial Cell- prokaryote Animal cell - eukaryote

Examples of Cell Types

http://w ww.uccs.edu/~rmelamed/MicroFall2002/Chapter%2011/Animal-like.htmlsrs.dl.ac.uk/Annual_Reports/AnRep01_02/anthrax.htm

Section 7.1 Summary – pages 171-174

The membrane-bound structures within eukaryotic cells are called organelles.

Each organelle has a specific function that contributes to cell survival.

Organelles of the Cell

Separation of organelles into distinct compartments benefits the eukaryotic cells.

All living cells must maintain a balance regardless of internal and external conditions. Survival depends on the cell’s ability to maintain the proper conditions within itself.

Why cells must control materials

The plasma membrane is the boundary between the cell and its environment.

Cell Membrane✓ Protection✓ Support✓ Selectively Permeable✓ Made of lipids &

proteins-phospholipid

✓ Fluid Mosaic Model

Summary Section 2 – pages 175-178

It is the plasma membrane’s job to:

-allow waste and other products to leave the cell.

-remove excess amounts of these nutrients when levels get so high that they are harmful.

-allows a steady supply of glucose, amino acids, and lipids to come into the cell no matter what the external conditions are.

■ This process of maintaining the cell’s environment is called homeostasis.

■ Selective permeability is a process used to maintain homeostasis in which the plasma membrane allows some molecules into the cell while keeping others out.

Structure of the Plasma Membrane

The plasma membrane is composed of Phospholipid bilayer back-to-back.

Phospholipids are lipids with a phosphate attached to them.

The fluid mosaic model describes the plasma membrane as a flexible boundary of a cell. The phospholipids move within the membrane.

Phospholipid Bilayer Make-up

Summary Section 2 – pages 175-178

Other components of the plasma membrane:

Cholesterol plays the important role of preventing the fatty acid chains of the phospholipids from sticking together.

Cholesterol

Molecule

Cell Membrane is made of:

a) Phospholipid Bilayer (double layer)

b) Proteins (Cholesterol)

c) Carbohydrates

THE NUCLEUS

The “brain” of the cell

■ Most prominent in eukaryotic cells

■ Nuclear membrane- maintains the shape

■ Has a double membrane■ Contains chromatin-

chromosomes-DNA & protein■ Nucleolus-ribosomes synthesize

& assemble here. RNA must go here to get instructions.

The nucleus is the central membrane-bound organelle that manages cellular functions.

Organelles of the Cell

Section 3 Summary – page 179-187

Nucleus and cell control

Chromatin

Nucleolus

Nuclear Envelope

The Cytoplasm

The jelly-like substance that holds all the organelles between the cell membrane and

the nucleus.

AKA - Cytosol

10 Cell Facts

1. Cells are too small to be seen without magnification.

2. There are two types of cells: prokaryote and eukaryote

3. Prokaryotic single-celled organisms were the earliest and most primitive forms

of life on earth.

4. There are more bacterial cells in the body than human cells.

5. Cells contain genetic material.

6. Cells contain structures called organelles which carry out specific functions.

7. Different types of cells reproduce through different methods.

8. Groups of similar cells form tissues.

9. Cells have varying life spans.

10. Cells commit suicide

Quick Recap.......

1. What are the two main types of cells?

2. Which one is larger?

3. Which one does not have a membrane bound nucleus?

4. What are the three main parts of the cell (that all cells

have)?

5. What are the 3 components of the cell theory?

6. What theory explains how eukaryotes evolved?

Section 3 Summary – page 179-187

The cell wall • The cell wall is a fairly rigid structure located outside the cell membrane that provides additional support & protection.

• Found only in plant, bacteria, and fungi.

• The cell wall is not found in animal cells.•Made of Cellulose in Plants, Chitin in

Fungi and Peptidoglycan in Bacteria.

• Two parts- primary & secondary

Endoplasmic Reticulum

Smooth or Rough

AKA “ER”

Assembly, Transport, and Storage

The endoplasmic reticulum (ER) is an organelle that is suspended in the cytoplasm and is the site of cellular chemical reactions.The “interstate” of the cell.

Two Types of ER■ Rough-studded with ribosomes, used to make large

amounts of proteins.

■ Smooth - involved in synthesis of steroids, regulates calcium levels, breaks down toxic substances

Figure 4.10a

Ribosomes

“Protein Factories”

■ The most numerous organelle.■ They make proteins for the cell

and to export from the cell.■ Some are free floating and some

are attached to other organelles

Ribosomes

Assembly, Transport, and Storage

Endoplasmic Reticulum (ER)

Ribosomes

Golgi ApparatusOther names include:

Golgi ComplexGolgi Body

The Golgi Apparatus

■ Processes the proteins made in the ER.■ Packages the proteins to be shipped.■ Secretes the proteins to their appropriate

destination.■ Series of flattened sacs that are convex

shaped.■ Vesicles - general name for small sacs

used to move materials from place to place.

The “UPS” of the Cell

Section 3 Summary – page 179-187

Assembly, Transport, and Storage

Golgi Apparatus

Lysosomes

The “Lysol” of the cell

Lysosomes - Intracellular Digestion Centers -

nickname "Lysol"

--vesicles that are used to digest

--contain high levels of degrading

enzymes

(to "lyse" means to dissolve)

--recycle old cell parts

--"suicide sac" - apoptosis

--digest other particles taken in by

phagocytosis

--this "food" is stored in food

vacuoles, the lysosomes fuse with

the vacuoles and release digestive

enzymes

--found in animal cells

TAY-SACHS disease – missing an

enzyme of the lysosomes that breaks

down a fatty substance. Over time this

fat builds up in the brain and nervous

tissue, smothering the cells. Results in

degeneration and death.

Section 3 Summary – page 179-187

Mitochondria are membrane-bound organelles in plant and animal cells that transform energy for the cell.

Mitochondria and energy

• A mitochondria has a highly folded inner membrane called the Cristae.

• Energy storing molecules called ATP are produced on inner folds.

Vacuoles and storageVacuoles are membrane-bound spaces used for temporary storage of materials. Notice the difference between vacuoles in plant and animal cells.

VacuoleAnimalCell

PlantCell

Smaller, less noticeable Larger, takes up more space

■ Vacuoles - can be found in animal cells but primarily found in plant cells.

■ A storage chamber for enzymes & metabolic waste.

■ Can make-up 90% of the volume of the plant cell.

■ They push other organelles to the side of the cell in the plant cell.

Vacuoles and storage

Section 3 Summary – page 179-187

Energy Transformers: Chloroplasts are cell organelles that capture light energy and produce food to store for a later time.

• The chloroplasts belongs to a group of plant organelles called plastids, which are used for storage.

• Plastids are double-membrane.

• Chloroplasts contain green pigment called chlorophyll. Chlorophyll traps light energy and gives leaves and stems their green color.

•--functions to convert light energy to carbohydrates

•--carbohydrates then broken down in mitochondria to produce

ATP

--consists of grana, closed compartments that are stacked

--thylakoids are the individual disk shaped compartments that make

up the grana (stack of thylakoids)

--stroma is the fluid surrounded the thylakoids

Cells have a support structure called the cytoskeleton within the cytoplasm.

The cytoskeleton is composed of microtubules and microfilaments.

Microtubules are thin, hollow cylinders made of protein and microfilaments are thin solid protein fibers.

Support & Locomotion

CentriolesA type of microtubule that aids in cell division of animal cells. They resemble a bundle of sticks.

Cilia are short, numerous, hair-like projections that move in a wavelike motion.

Cilia and flagella

Cilia

Some cell surfaces have cilia and flagella, which are structures that aid in locomotion or feeding.

Cilia and flagella can be distinguished by their structure and by the nature of their action.

Flagella are long projections that move in a whip-like motion.

Flagella and cilia are the major means of locomotion in unicellular organisms.

Cilia and flagella

Mini Quiz

1. What part of the cell

produces vesicles for export?

2. What part of the cell makes

proteins?

3. What part of the cell

produces ATP?

4. What part of the cell

transports materials throughout

the cytoplasm?

What is this structure?

Figure 4.7b

Figure 4.16b

What is this structure?

What is this structure?

What is its function?

Cell Size is limited by 3 things:

DNA - if there is not enough DNA, then the

cell can’t make enough proteins to function.

Surface area to volume ratio - bigger is not

always better. Cells need more SA and less

volume to be able to diffuse materials.

DIFFUSION RATE - faster rate equals more

food and less waste inside the cell

Diffusion●The movement of molecules from

an area of high concentration to an

area of low concentration

●Molecules tend to “spread out”

●Requires no energy

Equilibrium

When molecules are evenly spread

throughout a space

Osmosis

●The diffusion of water

across a membrane

●The cell membrane is

selectively permeable

How osmosis works

Rule for Osmosis

If the area outside the cell has more salt

– then water will be sucked out of the

cell

■ Unequal distribution of particles, called a concentration gradient, is one factor that controls osmosis.

What controls osmosis?

BeforeOsmosis

AfterOsmosis

Water molecule

Sugar moleculeSelectively permeable membrane

The difference in the concentration of a substance from one location to another.

■ Most cells whether in multicellular or unicellular organisms, are subject to osmosis because they are surrounded by water solutions.

Cells in an isotonic solution

H2O

H2O

Water Molecule

Dissolved Molecule

■ In an isotonic solution, the concentration of dissolved substances in the solution is the same as the concentration of dissolved substances inside the cell.

Cells in an isotonic solution

■ A plant cell has its normal shape and pressure in an isotonic solution.

■ In an isotonic solution, water molecules move into and out of the cell at the same rate, and cells retain their normal shape.

Cells in a hypotonic solutionIn a hypotonic solution, water enters a cell by osmosis, causing the cell to swell.Contractile Vacuoles remove excess water. H2O

H2O

Water Molecule

Dissolved Molecule

▪ Cytolysis the bursting due to the swelling of the cell from diffusion of water into the cell.

Cells in a hypotonic solution

■ Plant cells swell beyond their normal size as pressure increases.

▪ Turgor pressure the pressure water molecules exert on cell walls to help the plant maintain uprightness.

Cells in a hypertonic solution

■ In a hypertonic solution, water leaves a cell by osmosis, causing the cell to shrink. H2O

H2O

Water Molecule

Dissolved Molecule

▪ Plasmolysis the loss of pressure in plants due diffusion of water out of the cell that causes the plant to wilt.

Cells in a hypertonic solution

■ Plant cells lose pressure as the plasma membrane shrinks away from the cell wall.

This is the cell

membrane. What is

going to happen to the

cell wall if water is not

added to the cell soon?

1. Why is the water moving toward the left side of the beaker?

2. Which side of the beaker is hypertonic?

3. What is the solute?

Passive Transport

■ When a cell uses no energy to move particles across a membrane passive transport occurs.

Concentration gradientPlasma

membrane

Passive Transport by proteins■ Passive transport of materials across the

membrane using transport proteins is called facilitated diffusion.Some transport proteins, called channel proteins, form channels that allow specific molecules to flow through.

Plasma membrane

Channel proteins

Concentration gradient

Passive transport by proteinsThe movement is with the concentration gradient, and requires no energy input from the cell. Carrier proteins change shape to allow a substance to pass through the plasma membrane.In facilitated diffusion by carrier protein, the movement is with the concentration gradient and requires no energy input from the cell.

Concentration gradientPlasma

membrane

Step 1 Step 2

Carrier proteins

Active Transport

Movement of materials through a membrane against a concentration gradient is called active transport and requires energy from the cell. In active transport, a transport protein called a carrier protein first binds with a particle of the substance to be transported.

Plasma membrane

Concentration gradient

Carrier proteins

Cellular energy

Step 1 Step 2

Transport of Large Particles

■ Endocytosis is a process by which a cell surrounds and takes in material from its environment.

EndocytosisExocytosis

Digestion

Nucleus

Wastes

Types of Endocytosis■ Pinocytosis – the process of the cell

taking in fluid or cell “drinking”■ Phagocytosis – the process of the cell

taking in food particles or cell “eating”

■ Both of these require energy of the cell.

The material is engulfed and enclosed by a portion of the cell’s plasma membrane.

Transport of Large ParticlesExocytosis is the expulsion or secretion of materials from a cell.

EndocytosisExocytosis

Digestion

Nucleus

Wastes