CELL BIOLOGY Part I: Cell Theory, Cell Comparisons and Cell

Structures

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CYTOLOGY

The study of cells

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CELLS

Basic unit of structure and

function in all living things

Basic building block of life

Smallest unit of life

Few can be seen with

naked eye

Most need microscope to be

seen

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ORGANISM VARIATIONS

Unicellular organisms

Made up of one cell

Examples: amoeba, paramecium

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ORGANISM VARIATION

Multicellular organism

Made up of 2 or more cells

Examples: plants, animals, some

fungus, some protists

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CELL THEORY

Knowledge of cells began with

the invention of the microscope

in the late 1500’s

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CELL THEORY

Robert Hooke (1665) Built and used compound light

microscopes

Looked at cork from the bark of an oak tree under microscope – saw cork had “empty spaces” – reminded him of rooms in a monastery called cells

Coined term “cells” in book Micrographia

We know his cells were not alive but he could see the cell walls of plant cells

He was accepted as the first person to see and identify cells

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CELL THEORY

Anton van Leeuwenhoek (1674)

Saw first living cells

Bacteria, blood, sperm and protists in

water

Could see cells had parts

Made over 500 simple microscopes

A few are still around today

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CELL THEORY

Matthias Schleiden (1838)

Botanist

Proposed that all plants were

composed of cells

Contributions to Phytogenesis

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CELL THEORY

Theodore Schwann (1839)

Zoologist

Proposed that all animals are made of

cells

Microscopic Investigations on the

Accordance in the Structure and Growth of

Plants and Animals

Became known as the Father of Cytology

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CELL THEORY

Rudolf Virchow (1855)

Physician

Proposed that cells arise from pre-

existing cells “Omnis cellula e cellula”

Contradicted spontaneous generation

theory

Idea that nonliving things could give rise to

living things.

Die Cellularpathologie

Founder of cellular pathology

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CELL THEORY

Cell Theory

All living things are made of cells

Cells are the basic unit of structure and

function in all living things

All cells come from pre-existing cells

The combined contributions of these

five scientists led to the development

of the Cell theory

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CELL COMPARISONS

All cells have:

Cell membrane – selective barrier that

contains cytosol and ribosomes

Cytosol – semifluid, jellylike substance

enclosed by cell membrane

Ribosomes – tiny complexes that make

proteins according to instructions from

genes

Chromosomes – carry genes in the

form of DNA

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CELL COMPARISONS

Prokaryotic versus Eukaryotic 1/1

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Bacterium

(colored SEM; magnification 8800x)

CELL COMPARISONS

Prokaryotic cells

No membrane bound organelles

No nucleus

DNA in cytosol; concentrated in area called

nucleoid

10 times smaller than eukaryotic cells

Divide by binary fission, not mitosis

Prokaryotic organisms: all bacteria

Domain Bacteria and Domain Archaea

Kingdoms Eubacteria and Archaebacteria

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PROKARYOTES

Three types of bacteria based on

shape Rod shaped – Bacilli

Sphere shaped – Cocci

Corkscrew shaped – Spirochette or Spirilla

Various metabolism based on

environmental levels of O2 Aerobic – need O2, cannot grow without it

Anaerobic – Poisoned by O2; use ion of NO3- or

SO4- for energy

Facultative – able to use both O2 or ions

depending on environment

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PROKARYOTES

Ecological role

Decomposers

Symbiotic relationships

Can be:

Photoautotrophs

Chemoautotrophs

Photoheterotrophs

Chemoheterotrophs

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CELL COMPARISONS

Eukaryotic cells

Membrane bound organelles

True nucleus that contains DNA

10x larger than prokaryotic cells

Divide by mitosis

Eukaryotic organisms: Everything except bacteria

Domain Eukarya

Kingdom Animalia

Kingdom Plantae

Kingdom Fungi

Kingdom Protista

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CELL COMPARISONS

Plant versus Animal

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CELL COMPARISONS Plant cells have structures animal

cells do not have:

Cell wall

Provides structure and protection

Large central vacuole

Supports and gives shape to cell

Site of storage, hydrolysis of macromolecules and

breakdown of waste products

Chloroplasts

Site of photosynthesis

Plasmodesmata

Channels through cell walls that connect the

cytoplasm of adjacent cells

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CELL COMPARISONS

Animal cells have structures

plant cells do not have

Lysosomes

Digestive organelle where macromolecules

are hydrolyzed

Centrosomes with centrioles

Region where the cell’s microtubules are

initiated; contains a pair of centrioles

Flagella

Locomotion organelle present in some

animal cells

May be present in some plant sperm - rare

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CELL SIZE LIMITATIONS

Cell size is limited.

As cell size increases, a cell’s ability to

exchange materials with its

environment becomes limited by the

amount of membrane area that is

available for exchange.

Therefore the ratio of surface area to

volume is critical.

The larger the ratio (the difference)

between the two the better.

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CELL SIZE LIMITATIONS

As a cell (or any other object) increases

in size, its volume grows proportionately

more than its surface area. Area is proportional to linear dimension squared

Volume is proportional to linear dimensions cubed.

A smaller cell has a greater ratio of

surface are to volume Divide surface area by volume – the larger the number the

better!

It is better able to transport materials efficiently

from the membranes of the cell to all interior

regions of the cell.

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CELL SIZE LIMITATIONS

Larger organisms do not generally have larger

cells than smaller organisms – simply more

cells.

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CELL STRUCTURES AND

ORGANELLES

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CELL STRUCTURES

Cell Wall

Rigid, stiff barrier surrounding some

cells

Plants, bacteria, fungal, some protists

Made of carbohydrates

Cellulose in plants, peptidoglycogen in

bacteria, chitin in fungus

Supports and protects the cell

Located outside the cell membrane

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CELL STRUCTURES

Cell Membrane

Thin flexible barrier surrounding all

cells

Composed of a phospholipid bilayer

Serves as a selective barrier

Controls what enters and exits the cell

Supports and protects the cell

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CELL STRUCTURES

Cytoplasm

Interior of prokaryotic cell and the

region between the cell membrane and

the nucleus in eukaryotic cells

2 parts

Cytosol

The fluid portion of the cytoplasm

Organelles

Specialized structures in the cytoplasm of cells

that perform specific functions

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NUCLEUS AND ITS PARTS Nucleus

Only found in eukaryotic cells

Largest structure in cell

Usually located near center of cell

Surrounded by nuclear membrane

Double membrane that contains thousands of

pores that allow material to move in and out

Directs most of the cell’s activities

Contains most of the cell’s genetic material

Most contain nucleolus

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Nucleus contains chromosomes

Structures that carry genetic information

Chromatin – combination of proteins and

DNA that makes up chromosomes

Granular material visible within the nucleus

When cells divide, a strand of chromatin

coils up, condenses and becomes a

chromosome

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Nucleus contains nucleolus

Small, dense region inside nucleus

Produces RNA – 3 types

rRNA – actual ribosomes

mRNA – messenger RNA

Messenger of code from nucleus to ribosomes

tRNA – Transfers individual Amino Acid to

ribosome

Uses complementary code of mRNA

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NUCLEUS AND ITS PARTS

NUCLEUS AND ITS PARTS 1

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ENDOMEMBRANE SYSTEM

Organelles work together to

synthesize proteins and

transport them into membranes,

into organelles, or out of the cell.

Endoplasmic reticulum

Rough endoplasmic reticulum

Smooth endoplasmic reticulum

Golgi apparatus

Lysosome

Vacuoles (transport vesicles)

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ORGANELLES

Ribosomes

Very small and abundant

Made of RNA with proteins attached

Carry out protein synthesis

2 kinds

Free ribosomes – freely float in cytosol - make

proteins for the cell that they are in

Attached/ bound ribosomes – attached to

endoplasmic reticulum and make proteins for

transport out of cell

Pancreatic cells excrete the protein insulin to blood

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ORGANELLES

Smooth Endoplasmic Reticulum

No ribosomes attached; looks “smooth”

Internal membrane system

Involved in the synthesis of lipids

Metabolism of carbohydrates

Stores and regulates calcium levels

Breaks down toxic substances

Drugs and poisons

Increase SER, increase tolerance

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ORGANELLES

Rough Endoplasmic Reticulum

Internal membrane system

Ribosomes dotted all over its surface making

it look “rough”

Protein factory

Proteins made on attached ribosomes

Proteins migrate through rough ER

This is where they will fold into 3D shape

Proteins are modified by having carbohydrates attached

Proteins are released from rough ER in transport vesicles

which bud from regions of the rough ER

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ORGANELLES

Rough Endoplasmic Reticulum

Membrane factory

Grows in place by adding membrane

proteins and phospholipids to its own

membrane

Portions of the rough ER can then break

off and go to where additional membrane

is needed

Cell membrane

Other organelles

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ROUGH ENDOPLASMIC RETICULUM 1

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ORGANELLES

Transport vesicles

Bud off from endoplasmic

reticulum

Deliver packages (proteins, etc.) to

other areas of the cell (Golgi

apparatus) or to cell membrane for

export

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TRANSPORT VESICLES 1

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ORGANELLES 1

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Golgi Apparatus

Stacks of flat membranes

Has two sides – a receiving end and a shipping end

Receiving end receives products from the ER

Shipping end send modified products to other destinations

Contains enzymes that process, package, sort,

and secrete substances produced by the cell Products of the ER, such as proteins, are modified and

stored and then sent to other destinations.

Buds off to form: Secretory vesicles containing proteins to be secreted

Golgi vesicles containing membrane components to fuse with

cell membrane

Vesicles containing digestive enzymes that become lysosomes

GOLGI APPARATUS 1

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ORGANELLES Lysosomes

Made by rough ER and modified in Golgi

apparatus

Membranous sac of hydrolytic enzymes

that an animal cell uses to digest

macromolecules

Filled with proteins (enzymes) that:

Digest macromolecules (food), bacteria and viruses

Break down old organelles for recycling

Tay-Sachs disease Lipid-digesting enzyme in lysosomes is missing or inactive

– brain becomes impaired by accumulation of lipids in the

cells.

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LYSOSOME ACTION 1

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LYSOSOME ACTION 1

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ORGANELLES

Vacuole

Sac like structures filled with liquid

that store food, water, minerals,

enzymes and waste products

In plants only 1 large, centrally located

vacuole

Increase surface area of plant cells

Smaller versions called food vacuoles or

contractile vacuoles on other organisms

Food vacuoles for phagocytosis

Contractile vacuoles in freshwater protists

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PLANT CENTRAL VACUOLE 1

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ENDOMEMBRANE SYSTEM 1

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ENDOMEMBRANE SYSTEM

Endomembrane system

These organelles work together to

synthesize proteins and transport them

into membranes, into organelles, or out of

the cell.

The membranes of these organelles are

related through direct physical contact or

by tiny vesicles

Endoplasmic reticulum (Rough and Smooth)

Golgi apparatus

Lysosome

Vacuoles (transport vesicles)

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ENDOMEMBRANE SYSTEM Ribosomes on the RER make proteins.

These proteins are destined to leave the cell.

The proteins move into the RER

In the RER the protein folds into its specific shape

The RER modifies the protein

This often means adding carbohydrates to the protein

The proteins leave the RER in vesicles that are like

bubbles that bud off of the RER

The transport vesicles transport the proteins from the

RER to the Golgi apparatus

Here the proteins are further modified, stored and

eventually sent to other locations

More transport vesicles bud off the Golgi and transport

the proteins to the cell membrane to be released from the

cell.

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ENDOMEMBRANE SYSTEM 1

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ENDOMEMBRANE SYSTEM 1

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ORGANELLES

Mitochondria

Site of cellular respirations which

provides chemical energy (ATP) from

food through chemical reactions

Powerhouse of the cell

Has double membrane

Outer layer is smooth

Inner layer has many long folds called

cristae

Increases inner surface area to create more space

for the chemical reactions

Contains its own DNA

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MITOCHONDRIA 1

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ORGANELLES

Chloroplast

Site of Photosynthesis

Creates food energy from light energy through

chemical reactions

Has double membrane

Only found in plants and some protists

Contains chlorophyll

green pigment that absorbs light energy

Contains its own DNA

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CHLOROPLAST 1

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ORGANELLES Peroxisomes

Membranous sacs that contain oxidase

enzymes to detoxify harmful substances in the

liver and kidneys

Enzymes break down various toxins by transferring

hydogen from the toxin to oxygen (O2) creating

hydrogen peroxide (H2O2)

Hydrogen peroxide is toxic but peroxisomes also

contain an enzyme (catalase) that converts H2O2 to

H2O

Lysosomes break down alcohol, Formaldehyde and free

radicals

Free radicals are highly reactive chemicals with unpaired electrons that

can change the structure of proteins and nucleic acids

Normal products of cellular metabolism

If allowed to accumulate can destroy cells

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METABOLIC ORGANELLES 1

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CYTOSKELETON

Network of structures that support

and protect cell

Made of different types of proteins

3 types

Microtubules

Intermediate filaments

Microfilaments

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CYTOSKELETON

Microtubules

Largest – 25nm

Hollow tubes made of tubulin

Maintain cell shape

Make up cilia and flagella for cell

motility

Chromosomes movement

Organelles movement

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CYTOSKELETON

Microfilaments Smallest – 7 nm

Two strands of actin fibers intertwined Also called actin filaments

Maintain cell shape

Muscle contraction

Cleavage furrow formation during cell

division in animal cells

Cell motility - pseudopodia movement

Cytoplasmic streaming Circular flow of cytoplasm common in large plant

cells, speeds the distribution of materials within

the cell.

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CYTOSKELETON

Intermediate filaments

Intermediate size – 8-12 nm

Thick cables of many keratin fibers

coiled together

Maintain cell shape

Anchorage of nucleus and other

organelles

Formation of nuclear lamina

Lines interior of nucleus and

maintains the shape of the nucleus

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CYTOSKELETON Centrosomes and Centrioles

Centrosome

Region located near the nucleus

Considered a microtubule-organizing

center

Microtubules grow out of the centrosome

Centrioles

Paired organelles found within centrosome

Replicate before animal cell divides

Thought to help with cellular reproduction by

making sure each cell receives a complete set of

chromosomes

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CENTRIOLES 1

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CYTOSKELETON AND MOTILITY

Three types of cell movement:

Cilia

Flagella

Pseudopodia

Functions:

Move cell through environment

Move materials over cell’s surface

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CYTOSKELETON AND MOTILITY

Cilia

Short whip-like extensions on surface of cell

that move substances along the cell surface

Made up of microtubules

Usually occur in large numbers

Example: Line trachea and sweep debris from lungs

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CYTOSKELETON AND MOTILITY

Flagella

Long whip-like extensions on surface of cell

that move the entire cell

Made up of microtubules

Usually only one or a few per cell

Examples: Sperm of animals, algae, some plants

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CILIA AND FLAGELLA

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CILIA AND FLAGELLA 1

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CYTOSKELETON AND MOTILITY

Pseudopodia

Amoeboid movement

A cell such as an amoeba crawls along a surface

by extending and flowing into cellular

extensions called pseudopodia

Ooze forward and then collect back together, only to

ooze forward again

Uses microfilaments

Examples: amoeba, white blood cells

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CYTOSKELETON AND MOTILITY

Cell motility (movement) also

involves the cytoskeleton

Cilia and flagella are extensions

projecting from some cells that contain

microtubules arranged in a 9+2

pattern

9 sets of microtubules are arranged in a

ring and in the center of the ring are two

single microtubules

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9 + 2 PATTERN OF MICROTUBULES

IN CILIA AND FLAGELLA 1

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