Cell Structure and Function

Preview

• Cell characteristics and cell theory

• Overview of cell membrane

• Eukaryotic cells

• Eukaryotic organelles

• Prokaryotic cells

• How Cells Move

• Smallest unit of life

• Can survive on its own or has potential to do so

• Senses and responds to environment

• Has potential to reproduce

• Differ in:– Size– Shape – functions

Characteristics of Cells

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Cell Theory

1) Every organism is composed of one or

more cells

2) Cell is smallest unit having properties of

life

3) Continuity of life arises from growth and

division of single cells

Structure of Cells

All cells have three distinct sections:

Plasma Membrane

Nucleus (or nucleoid region in prokaryotes)

Cytoplasm

Cell• Plasma Membrane

• Nucleus

• Cytoplasm

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Preview of Cell Membranes

Plasma membranes are composed mostly of a lipid bilayer that prevents free passage of water soluble substances across it.

one layerof lipids

one layerof lipids

8Plasma Membrane

Other names for a cell membrane:

• Cytoplasmic membrane

• Semipermeable membrane

• Phospholipid bilayer

Eukaryotic Cells

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• Have a nucleus 

• Have organelles – small, membrane bound “organs” in the cell that perform a specific job for the cell.

• Found in the Protista, Fungi, Plant, and Animal kingdoms

• Have 1000 times more DNA than prokaryotic cells

Organelle Functions

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nucleus - controls the cell’s activities Nuclear membrane – separates cytoplasm from

nuclear materialNucleolus – site of RNA and ribosome synthesisDNA – genetic material

cytoplasm – Space between nucleus and plasma membrane(cytosol) jellylike substance that fills the inside of a

cell , gives structure and shape

Cont.

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endoplasmic reticulum - "tunnels" in the cytoplasm that allow materials to move through the cell easier (subway system of the cell)Rough (RER) – makes proteins, covered in ribosomesSmooth (RER) - makes lipids, degrades fats,

detoxifies materialribosomes – attached to ER and scattered in cytoplasm,

make proteins mitochondrion – powerhouse, produce energy in the cell Golgi body - stores, processes, and secretes proteins

and lipids (post office)

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• vesicle- sacs that transport material in cell

• centrioles – centers that produce and organize structures that help in cell reproduction (animal cells only)

• lysosome – digest, recycles nutrients (suicide sack)

• cytoskeleton – structurally supports, gives shape & helps move cell components

Quick Check

1. List two parts of the cell theory.

2. Rough endoplasmic reticulum is responsible for making ___ for the cell.

3. List the four eukaryotic kingdoms

4. Centrioles are only found in ___ cells.

Eukaryotic Animal Cell Structure

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Plant vs. Animal Cell

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Plant Cells Only

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• cell wall - rigid surrounding of plant cells, protects, structural to support

• chloroplasts - contain chlorophyll in plants; this is where the plant’s food is produced by photosynthesis

• vacuoles - large bodies in plant cells that hold water, waste, etc.

A closer look at major organelles

19A closer look at the nucleus:

Nuclear Envelope/Membrane20

• Double lipid membrane with pores• Controls what goes in and out

–Pores control ions & water soluble materials entrance and exit

• Ribosomes on outer membrane • Membrane merges with ER• Nucleoplasm - semifluid interior of nucleus

Nuclear Envelope

Nucleolus

Mass of proteins that codes for rRNA (ribosomal RNA)

Synthesis of ribosomes and proteins

Genetic Material (DNA)

• Chromosome – one DNA molecule and the many proteins that are associated with it

• Chromatin – total collection of all DNA molecules and their associated proteins

• DNA + proteins=

chromatin

Chromatin strands

bunched together=

chromosome

A closer look at ER:

• Endoplasmic reticulum

• A flattened channel that starts at the nuclear envelope/membrane and folds back and forth

• Two typesRough (RER)– Has ribosomes attached

• Makes proteins

Smooth (SER)– Detoxifies drugs, makes lipids

A closer look at Golgi bodies:

• Vesicles pinch off of ER.• Fuse with Golgi bodies• Golgi bodies repackage and ship vesicles by

adding or removing molecules to proteins and lipids.

• Think post office

and stacks of

pancakes with

syrup!

A closer look at lysosomes:

• membrane-enclosed vesicles that contain powerful digestive enzymes – internal pH reaches 5.0

• Functions– digest foreign substances

and recycles own organelles– Autolysis– Suicide sac

Tay-Sachs Disorder

• Affects children of eastern European descent• Genetic disorder caused by absence of single

lysosomal enzyme– enzyme normally breaks down glycolipid

commonly found in nerve cells– as glycolipid accumulates, nerve cells lose

functionality– chromosome testing now available

A closer look at mitochondria:

• Mitochondria resemble bacteria– Have DNA, ribosomes– Divide on their own

• May have evolved from ancient bacteria that were engulfed but not digested

• Mitochondrial DNA (genes) are usually inherited only from the mother.

Mitochondria (cont.)• Double outer membrane• Inner folded membrane• Site of most of cells ATP

production• Only in eukaryotic cells• Site of aerobic respiration

(oxygen present)• Numerous in skeletonal cells

A closer look at chloroplasts (and other plastids):

• Plastids • Are organelles that function in

photosynthesis or storage in plants.• Three types

– Chloroplast– Chromoplasts– Amyloplasts

Cont.Chloroplast – • Conduct

photosynthesis• Enclosed by a double

membrane• Thylakoid stacks of

grana – Contain pigments

such as chlorophyll• Stroma fluid filled area

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Other Plastids

• Chromoplasts – No chlorophyll

– Abundance of carotenoids

– Color fruits and flowers red to yellow

• Amyloplasts– No pigments

– Store starch (tubers- potatoes)

A closer look at plant cell walls:

• Surrounds the plasma membrane

• Protects, supports and give shape to cell

• Porous – allows water and solutes to pass in/out

• In all plants

• Some protist and fungi

• Cuticle on outer most surfaces of plants

Even Cells Have a Skeleton• Cyto means cell

– So cytoskeleton means cell skeleton

• It is organized system of protein filaments in the cytoplasm.

• Some are permanent others are temporary

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Cytoskeletal Elements

microtubule

microfilament

intermediatefilament

Functions ofCytoskeletal Elements:

• Move organelles within the cytoplasm

• Assist in cell division

• Provide structure and support for the cell

• Can be used to identify cells

Prokaryotic Cells

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DNA is not enclosed in nucleus

Generally the smallest, simplest cells

No organelles

Most ancient form of life

Archaeans and bacteria the only representatives

Prokaryotic means “before the nucleus

Prokaryotic Cells

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Permeable, semi-rigid cell wall outside plasma membrane gives shape

Plasma membrane- semi-permeable to control what goes in and outCan contain pigments for photosynthesis

Polysaccharides are on surface to help them stick to objects or give a protective coating

1-2 Flagella – movement

Prokaryotic Cells

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Pili – helps stick to surfaces and exchange genetic material

Cytoplasm – semifluid material inside cellRibosomes – scattered in cytoplasm,

protein making siteNucleoid – concentrated region where DNA

is located. DNA is circular. Plasmids – scattered in cytoplasm, these

can confer selective advantages such as antibiotic resistance. Contain just a few genes.

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Prokaryotic Structure

DNA

pilus

flagellum

cytoplasm with ribosomes

capsulecell wall

plasma membrane

Quick Check

How Do Cells Move?

• Cells must have ATP in order for movement to take place.

• Cilia, flagella and false feet are all ways that cells move.

Cilia, Flagella and False Feet• Cilia

– many small projections on cell membranes working in together for movement

– Along trachea, oviducts in humans

• Flagella – generally 1-2 projections that move an object– Sperm is the only flagella in humans

• Pseudopodia– False foot– Temporary extension of cytoplasm for movement

Protists use all three.

• Cilia pseudopodia

• flagella

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Lab Notes

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Lead to the ability to develop the Cell TheoryCreate detailed images of something that is

otherwise too small to seeLight microscopes

Simple or compoundUses two sets of lenses to magnify the living or dead

image

Electron microscopesTransmission EM or Scanning EMUses electrons view either inside or surface of a dead

cell

Microscopes

New Terms

• Wavelength – distance from the peak of a wave to the peak of another wave

• Ocular Lens enlarges 10x inside the eye piece

• Objective lens magnify at various levels

• Stage supports the object viewed on slide

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• Create detailed images of something that

is otherwise too small to see

• Light microscopes

– Simple or compound

• Electron microscopes

– Transmission EM or Scanning EM

Microscopes

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Limitations of Light Microscopy

• Wavelengths of light are 400-750 nm

• If a structure is less than one-half of a wavelength long, it will not be visible

• Light microscopes can resolve objects down to about 200 nm in size

http://www.microscopepartsforsale.com/ccount12/click.php?id=2

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Electron Microscopy

• Uses streams of accelerated electrons rather than light

• Electrons are focused by magnets rather than glass lenses

• Can resolve structures down to 0.5 nm

SEM- surface views

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Electron Microscopes

TEM

SEM

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TEM- inside cell view

Image comparison

• The electron microscope allows a smaller object to seen

• The electron microscope is not limited by the wavelength of light

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