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Topic 2.3: Eukaryotic Cells

IB Biology HL

A. Allen

Cytoplasm (cytosol): a cell's inner space

cytosol

Cytosol: large fluid-filled space (mostly water + proteins that control

most of the cell metabolisms): glycolysis, transcription

factors, intracellular receptors etc.

Plasma

membrane

Organelles

• Nucleus

• Protein production machine: the ribosomes

• Mitochondria and Chloroplasts

• Endoplasmic Reticulum and the Golgiapparatus (we don’t say ‘Golgi body’ in IB)

• Lysosomes

• Adapted and/or specialized for carrying out one or more vital functions

Reminder! Membrane-bound

organelles are only found in

eukaryotes.

Nucleus: a cell's center

Function of the nucleus:

• Stores the chromosomes (genetic material) Note: Two kinds of genetic material:

– deoxyribonucleic acid (DNA)

– ribonucleic acid (RNA)

• Keeps the DNA molecules separated from metabolic machinery of cytoplasm.

• Makes it easier to

organize DNA and to

copy it before parent

cells divide into daughter

cells

• DNA replication and

synthesis of messenger

RNA (mRNA). The

mRNA is allowed to

leave the nucleus. It is

read by the ribosomes

during protein synthesis.

...Nucleus: a cell's center

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Nucleolus

• Dense mass of

material in nucleus

• Cluster of DNA and

proteins

• Subunits must pass

through nuclear pores

to reach cytoplasm

• production of

ribosomes in nucleolus

• Two outer membranes (lipid bilayers)

• Pores span bilayer and controls what

enters/leaves nucleus.

• Much more detail to follow!

Nuclear Membrane (Envelope)

Chromatin

• Cell’s collection of DNA and associated proteins

• A chromosome is one DNA molecule and its associated proteins

• Appearance changes as cell dividesFUNCTION:

• With the help of tRNA, ribosomes use information in mRNA to assemble proteins

• small semi-spherical, black dots

• some are free in cytoplasm (cytoplasmic ribosomes), others are attached to the ER (ER ribosomes)

Ribosomes

STRUCTURE

• ER is a continuation of the outer nuclear membrane.

• Two types: Smooth and Rough. (Rough ER has ribosomes on it)

• Network of membrane that connects nuclear envelope to the cell

membrane

Endoplasmic Reticulum (ER)

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FUNCTION:

• Smooth ER (no ribrosomes):

responsible for lipid and membrane

protein modifications). In some cells, it

regulates carbohydrate metabolism and

breaks down toxins and drugs

• E.g., in liver, metabolizes alcohol and

barbiturates; in testes and ovaries,

synthesizes sex steroids; etc.

• Rough ER (has ribosomes on it)

responsible for the synthesis of other

proteins). The ribosomes assemble the

proteins within the rough ER. Once

assembled, the proteins pinch off the ER

and are released in a vesicle.

Endoplasmic Reticulum

Endoplasmic Reticulum (ER)

…Endoplasmic Reticulum (ER)

FUNCTION:

• processes, packages, and, secretes cell products (lipids & proteins)

• Put finishing touches on proteins and lipids that arrive from ER

• Package finished material for shipment to final destinations. (Exocytosis)

• Material arrives

and leaves in vesicles

Golgi Body (Golgi Apparatus) Golgi Apparatus

…Golgi Body (Golgi Apparatus)

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STRUCTURE

• Double membrane. Inner membrane is

folded for greater surface area. Folds

are called cristae.

• Interior is called the matrix.

• Contain their own genome (distinct

from nuclear genome)

• Self-replicating

FUNCTION

• ‘burns’ food, i.e. glucose to release

energy. Energy is used to make ATP.

ATP is a high-energy molecule that

can be directly used by the cell.

Mitochondria

The “powerhouse” of the cell

…Mitochondria

TEM of Mitochondria

STRUCTURE

• Formed by Golgi bodies

• Bound by a single membrane

FUNCTIONS

• Digests the food particles inside the cell with help of enzymes. These enzymes work at low pH.

• Involved in autolysis (suicide of cell)

• Digest foreign bacteria that invade a cell

• Recycling of membrane components

• Repair damage to plasma membrane

Lysosomes

lysosomes McGraw Hill

Lysosomes

• Made by Golgi

• Surrounded by a single membrane

• Get rid of toxic substances

• Many in the liver/ brain

lysosome

Peroxisomes

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FUNCTION:

• maintains the shape of a

plant cell

• found in plants, some fungi,

some protists

• In plants, cell walls are made

of a polysaccharide called

cellulose.

• Structural component that

wraps around the plasma

membrane

Cell Wall …Cell Wall

FUNCTION:

• Photosynthesis: converts sunlight, carbon dioxide,

and water into sugar (makes food for plants)

Chloroplasts

• A large membrane bound sac

FUNCTION:

• storage area for proteins and

water

• Maintain structure in plant cells by means of turgor pressure

Vacuole

1.3 Eukaryotic Cells2.3.5 Describe three differences between plant and animal cells.

Carbohydrates

stored as starch.

Carbohydrates

stored as glycogen.

Stores large

amounts of liquid

(juice). Larger

size of cell.

√√√√Central VacuoleXDoes not store

large amounts of

liquid. Smaller

size of cell.

Rigid, cannot easily

change shape.√√√√Cell WallXFlexible, can easily

change shape.

Can produce its

own food.

√√√√ChloroplastXCannot produce its

own food

Plant CellsStructureAnimal Cells

• very complex and dynamic cell component!

• organizes and maintains the cell's shape (e.g. epithelial cells of the

gut)

• anchors the organelles in place

• helps during the uptake of external material (endocytosis)

• involvement in cell movement

• growth

Cytoskeleton: a cell's scaffold

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microtubules microfilamentsintermediate filaments

tubulin actin keratin family

All help maintain cell shape

Cilia, flagellaChromosome movementOrganelle movement

Cytoplasmic streamingPseudopodiaCell division

Nuclear laminaAnchorage of nucleus and some other organelles

...Cytoskeleton ...Cytoskeleton

...Cytoskeleton

Molecular

motors

...Cytoskeleton

Macrophage attacks bacteria

Microfilaments (actin) allow formation of pseudopods

...Cytoskeleton

Striated Muscle

...Cytoskeleton

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Centrosome:Made up of centriole pairs

...Cytoskeleton 2.3.4 Compare prokaryotic and eukaryotic cells.

• Prokaryotic cells have naked DNA which is found in the cytoplasm in a

region named the nucleoid. On the other hand, eukaryotes have

chromosomes that are made up of DNA and protein. These chromosomes

are found in the nucleus enclosed in a nuclear envelope.

• Prokaryotes do not have any mitochondria whereas eukaryotes do.

Prokaryotes make use of their cell surface membrane and mesosomes

instead.

• Prokaryotes have small ribosomes (70S) compared to eukaryotes which

have large ribosomes (80S).

• In prokaryotes there are either no organelles bounded by a single

membrane in comparison to eukaryotes which have many of them

including the Golgi apparatus and the endoplasmic reticulum.