Basic Structure of a Cell

1Adapted from work of CMASSENGALE

Main Characteristics of Living Things

1. Made of CELLS

2. Maintain HOMEOSTASIS

3. METABOLISM (produce and/or use energy)

4. RESPOND to stimulus

5. REPRODUCTION at species level

6. HEREDITY (DNA)

7. GROW and DEVELOP

8. EVOLVE as a species over generations

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LEVELS OF ORGANIZATIONNonliving Levels:

1. ATOM (element)

2. MOLECULE (compounds like carbohydrates &

proteins)

3. ORGANELLES (nucleus, ER, Golgi …)

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LEVELS OF ORGANIZATIONLiving Levels:

1. CELL (makes up ALL organisms)

2. TISSUE (cells working together

3. ORGAN (heart, brain, stomach …)

4. ORGAN SYSTEMS (respiratory, circulatory …)

5. ORGANISM

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LEVELS OF ORGANIZATIONLiving Levels continued:

1. POPULATION (one species in an area)

2. COMMUNITY (several populations in an area

3. ECOSYSTEM (forest, prairie …)

4. BIOME (Tundra, Tropical Rain forest…)

5. BIOSPHERE (all living and nonliving things on Earth)

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History of Cells & the Cell Theory

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Cell Specialization

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First to View Cells•In 1665, Robert Hooke used a microscope to examine a thin slice of cork.

•Cork consists of dead plant cell walls.

•What he saw looked like small boxes.

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First to View Cells

•Hooke is responsible for naming cells.

•Hooke called them “CELLS” because they looked like the small rooms that monks lived in called cells.

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Anton van Leeuwenhoek•In 1673, Leeuwenhoek(a Dutch microscope maker), was first to view organism (living things)

•Leeuwenhoek used a simple, handheld microscope to view pond water & scrapings from his teeth

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Beginning of the Cell Theory

• In 1838, a German botanist named Matthias Schleidenconcluded that all plants were made of cells

• Schleiden is a cofounder of the cell theory

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Beginning of the Cell Theory• In 1839, a German zoologist named Theodore Schwannconcluded that all animals were made of cells

• Schwann also cofounded the cell theory

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Beginning of the Cell Theory

• In 1855, a German medical doctor named Rudolph Virchow observed, under the microscope, cells dividing.

• He reasoned that all cells come from other pre-existing cells by cell division.

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CELL THEORY

• All living things are made of cells.

• Cells are the basic unit of structure and function in an organism (basic unit of life.)

• Cells come from the reproduction of existing cells (cell division.)

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Cell Size and TypesCells, the basic units of organisms, can only be observed under microscope.

Three basic types of cells include:

Animal Cell Plant Cell Bacterial Cell

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Number of Cells

Although ALL living things are made of cells, organisms may be:

Unicellular – composed of one cell

Multicellular- composed of many cells that may organize into tissues, organs, and so on.

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CELL SIZE

Typical cells range from 5 – 50 micrometers (microns) in diameter

Which Cell Type is Larger?

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> > Plant cell Animal cell Bacteria

What Cells Look Like

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Multicellular Organisms

Cells in multicellular organisms often specialize (take on different shapes and functions.)

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Cell Specialization

• Cells in a multi-cellular organism become specialized by turning different genes on and off

• This is known as DIFFERENTIATION

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Specialized Animal Cells

Muscle cells Red blood cells

Cheek cells

Organization Levels of Life

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Atoms to Organisms

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ATOMS ���� MOLECULES ���� ORGANELLES

Nonliving Levels

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CELLS –

life starts here

TISSUES –

Similar cells working together

Living Levels

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ORGANSORGAN

SYSTEMSORGANISM

Different tissues

working together Different organs

working together

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More Living Levels

Different organ systems

working together

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Simple or Complex Cells

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Prokaryotes – the first cells

• Cells that lack a nucleus or membrane-bound organelles

• Includes bacteria

• Simplest type of cell

• Single, circular chromosome

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Eukaryotes

• Cells that HAVE a nucleus and membrane-bound organelles

• Includes protists, fungi, plants, and animals

• More complex type of cells

Two Main Types of Eukaryotic Cells

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Plant Cell Animal Cell

Organelles

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Organelles

• Very small (microscopic)

• Perform various functions for a cell

• Found in the cytoplasm

• May or may not be membrane-bound

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Animal Cell Organelles

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Nucleolus

Nucleus

Nuclear envelope

Ribosome (attached)

Ribosome (free)

Cell Membrane

Rough

endoplasmic

reticulum

Golgi apparatus

Mitochondrion

Smooth endoplasmic

reticulum

Centrioles

Plant Cell Organelles

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• Composed of double layer of phospholipids interspersed with proteins (phospholipid bilayer)

• Surrounds cytoplasm of ALL cells

• Controls what enters and leaves the cell

Cell or Plasma Membrane

Outsideof cell

Insideof cell(cytoplasm)

Cellmembrane

Proteins

Proteinchannel Lipid bilayer

Carbohydratechains

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The Cell Membrane is Fluid

Molecules in cell membranes are constantly moving and changing.

COPYRIGHT CMASSENGALE 36

Cell Membrane Proteins

• Proteins help move large moleculesor aid in cell recognition

• Peripheral proteins are attached on the surface (inner or outer)

• Integral proteins are embedded completely through the membrane

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Cell Membrane in Plants

• Surrounds the

cytoplasm

• Pushes out against

the cell wall to

maintain cell shape

Cell membrane

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Cell Wall

• Supports and protects cell

• Found outside of the cell membrane

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Permeability Permeable: allowing substances to pass through

• Cell walls are semi-permeable based on molecule size.

• Cell membranes are selectively permeable based on

molecule recognition.

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Cytoplasm of a Cell

• Jelly-like substance

enclosed by cell

membrane

• Provides a medium

for chemical reactions

to take place

cytoplasm

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More on Cytoplasm

• Contains organelles to

carry out specific jobs

• Found in ALL cells

cytoplasm

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The Control Organelle - Nucleus

• Controls the normal

activities of the cell

• Contains the DNA in

chromosomes

• Bounded by a

nuclear envelope

(membrane) with pores

• Usually the largest

organelle

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More on the Nucleus

• Each cell has fixed

number of

chromosomes that

carry genes

• Genes control cell

characteristics

Nucleus

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Nuclear EnvelopeDouble membranesurrounding nucleus

Also called nuclear membrane

Contains nuclear poresfor materials to enter & leave nucleus

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Inside the Nucleus -

The genetic material (DNA) is found

DNA is spread out

And appears as

CHROMATIN

in non-dividing cells

DNA is condensed &

wrapped around proteins

forming

as CHROMOSOMES

in dividing cells

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What Does DNA do?DNA is the hereditary material of the cell

Genes that make up the DNA

molecule code for different

proteins (which means you)

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Nucleolus

Inside nucleus

Cell may have 1 to 3nucleoli

Disappears when cell divides

Makes ribosomes that make proteins

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CytoskeletonHelps cell maintain cell shape

Also help move organellesaround

Made of proteins

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Centriole

Found only in animal cells

Found near the nucleus

Centrioles:

Made of bundle of microtubules

Found in pairs

Form the mitotic spindle during cell division

Help to pull chromosome pairs apart

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Centrioles and the Mitotic Spindle

Made of MICROTUBULES (Tubulin)

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Mitochondrion(plural = mitochondria)

“Powerhouse” of the cell

Generate cellular energy (ATP)

More active cells like muscle cells have more mitochondria

Both plants and animal cells have mitochondria

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Mitochondria

Surrounded by a double outer

membrane

Has folded inner membrane

Rod shape

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Fact… Mitochondria come from cytoplasm in the egg cell during fertilization

Therefore …

You inherit your mitochondria (and mitochondrial DNA) from your mother

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Endoplasmic Reticulum - ERNetwork of hollow membranes

Connects to nuclear envelope and cell membrane

Functions in synthesis and transport of cell products

Two kinds of ER ---ROUGH & SMOOTH

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Rough ER

Has ribosomes on its surface

Makes, stores, and transports proteins

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Rough ER

Proteins are made by ribosomes on ER surface.

They are then threaded into the interior of the rough ER to be transported.

Examples:

•digestive enzymes stored in sacs until transported out of the cell

•proteins created and placed into cell’s membrane

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Smooth ER

Smooth ER lacks ribosomes on its surface.

Attached to the ends of rough ER.

Most cells have very little smooth ER.

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Functions of the Smooth ER

Functions:

•Makes lipids (fats)

•Makes steroids (in ovaries and testes makes estrogen and testosterone)

•Regulates calcium (heart and skeletal muscle, controls contractions)

•Detoxifies drugs and poisons (liver and kidney; contributes to drug tolerance)

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RibosomesMade of PROTEINS and rRNA

“Protein factories” for cell

Join amino acids to make proteins

Process called protein synthesis

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Ribosomes

Can be attached to Rough ER

(eukaryotic)

OR

Be free (unattached) in the cytoplasm

eukaryotic and prokaryotic

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Golgi Bodies

Stacks of flattened sacs

Receive proteins made by ER

Transport vesicles received by side nearest the nucleus and/or ER, passed through membranes, and exit the opposite side.

Transport

vesicles

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Golgi Bodies

Look like a stack of pancakes

Modify, sort, package, and label

molecules from ER for storage OR transport out of cell

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Golgi Animation

Materials are transported from Rough ER to Golgi

to the cell membrane by VESICLES

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Lysosomes

Bud from the golgi body

Membrane bound sacs

Contain digestive enzymes

Break down large molecules:• liver: break down glycogen for release of glucose into bloodstream

• white blood cells: break down bacteria

• digest worn out cell parts

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Lysosomes

Suicide SacsWhen it is time for a cell to die, lysosomes lyse (break open) themselves.

This results in the breakdown and digestion of the entire cell.

This “programmed cell death” is called autolysis and is critical to

maintaining and organism's health.

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Vacuoles

Fluid filled sacs for storage

Plant cells have a large Central Vacuole

Small or absent in animal cells

No vacuoles in bacterial cells

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Central Vacuole

Central vacuole stores mostly water and can take up 90% of the interior of a plant cell

In addition to water, they can also contain enzymes and wastes

Examples: ◦ Acacia trees store poisons◦ Tobacco plants store nicotine

Presence means it is

a plant cell

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Chloroplasts

Found only in plants

Use light energy to combine CO2 and water to make glucose (sugar)

Each chloroplast:

System of flattened membranous sacs called thylakoids

Thylakoids contain chlorophyll

Chlorophyll is the molecule that absorbs light energy

Chloroplasts can only arise by dividing existing chloroplasts

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Cilia and Flagella

Function in moving cells, in moving fluids, or detection of vibration.

Composed of microtubules

• Cilia are short and numerous

• Flagella are longer and fewer in number

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Cilia and Flagella

Bacteria

Sperm

Inner ear

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Cilia move like oars

Flagella move like a whip

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Cell Size

Cell size varies, but only within

a relatively small margin… the

size of an elephant cell is

approximately the same size of

a mouse cell.

Two important factors affecting cell size:

1. Type

2. Surface area to volume ratio

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Surface Area to Volume Ratio

Surface area (cell membrane surface) of a cell is important to allow nutrients in and to remove wastes

Volume of a cell is where all the life processes happen

Math dictates that volume increases FASTER than surface area

When the volume of the cell exceeds the membrane’s ability to regulate nutrients and wastes, the cell is too big and must divide

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Surface Area to Volume Ratio

The cell type can affect the surface area to volume ratio

The cell type is related to cell shape

Different shapes allow for different sizes, but the RATIO REMAINS WITHIN NARROW LIMITS