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The Ultrastructure of Cells

Topic 1
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flagella)
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Used for movement

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Used for attachment

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Joining of bacteria in preparation for the transfer of DNA from one cell to

➢ Pili

another
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Sexual reproduction

➢ Ribosomes
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Sites of protein synthesis

○

Free in the cytoplasm

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The Ultrastructure of Cells
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DNA is copied
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The cell divides into two identical daughter cells
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Biology SL

There are two kinds: the rough endoplasmic reticulum and the smooth
endoplasmic reticulum
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■

Rough ER
●

Has ribosomes on the surface

●

Produces various proteins for transportation to other cells

Smooth ER
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Has no ribosomes on the surface

●

Instead, on the surface, it has many unique enzymes filling
functions such as:
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Production of membrane (phospholipids)

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Production of sex hormones in ovaries and testicles

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Detoxification of drugs in the liver

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Storage of calcium ions in muscles

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Transporting lipid-based compounds

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Helping the liver release glucose into the bloodstream
when needed

➢ Golgi apparatus
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Consists of flattened sacs, called cisternae, stacked one on top of the other

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Collects, packages, modifies and distributes materials synthesized in the
cell

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One side of the apparatus is near the rough ER and is called cis side
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Where products are received

■

The discharging opposite side is the trans side

In glandular cells, such as those in the pancreas, the golgi apparatus can be
very large

➢ Ribosomes
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Don’t have exterior membranes

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Assemble proteins

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Either free (proteins to stay in cell) or attached to ER (proteins to go out of
the cell)

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Composed of RNA and protein

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80S
■

Same function, but are heavier than prokaryotes (70S)

➢ Cytoplasm
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The region inside all cells where organelles are found

○

There’s a fluid around organelles which is called cytosol

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The Ultrastructure of Cells

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crista), which provide a
huge surface within the organelle where chemical reactions can
occur

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Cellular respiration happens in the matrix
■

○

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A semi-fluid substance, similar to cytoplasm, within the organelle

Contain their own DNA and ribosomes
■

A circular chromosome like prokaryotes

■

70S ribosomes, the same as prokaryotic cells

■

Perform reproduction and produce their own proteins

Cells that have high energy requirement, like muscle cells, have many
mitochondria

➢ Nucleus
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Holds the DNA

○

Has a double membrane, called nuclear envelope
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Both are smooth

■

Contains small pores allowing communication

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The Ultrastructure of Cells
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2

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Helps to preserve shape

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Made of the carbohydrate cellulose

○

What the cell wall is made of depends on the organism
■

Biology SL

Different for bacteria, yeast, fungi, algae and plants

➢ Chloroplasts
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Occur only in algae and plant cells

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Have a double membrane

○

They have approximately the same size as bacteria

○

Have their own DNA and ribosomes (70S)

○

■

Able to reproduce and make their own proteins

■

DNA is in form of a ring

Contain grana, thylakoids and a stoma
■

Grana (sin
...
2

Biology SL

Prokaryotes & Eukaryotes
➢ Differences

Prokaryotic cells

Eukaryotic cells

DNA in a ring form without protein

DNA with proteins as chromosomes/

DNA free in the cytoplasm => nucleoid

DNA enclosed within a nuclear envelope

region

=> nucleus

No mitochondria

Mitochondria present

70S ribosomes

80S ribosomes

No internal compartmentalization to form

Internal compartmentalization = many

Size less than 10 μm

Size more than 10 μm

chromatin

organelles

organelles

➢ Similarities
○

Have plasma membrane

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Carry out the functions of life

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DNA present in both

○

Have ribosomes = produce proteins

Plant & Animal cells
➢ Similarities
○

○

Many organelles are shared
■

Golgi apparatus

■

Rough and smooth ER

■

Mitochondria

■

Ribosomes

■

Plasma membrane

■

Nucleus

■

vacuoles

The organelles shared have the same structure and function

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The Ultrastructure of Cells

Topic 1

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