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Chapter 3 - Cell Structure 
 
Eukaryotic Cells 
A cell that contains a true nucleus is called a ​eukaryotic cell​
...
 
 
Organelle 

Description 

Nucleus 

Largest​ cell organelle
...
 
Contains small nuclear 
pores​ to allow proteins to 
move out of the nucleus
...
 

● Controls the ​activity​ of the 
cell
...
 

Nucleolus 

1-2 micrometers in 
diameter
...
 

● Where ​ribosomes​ are 
made
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The outer layer is 
continuous with the RER 
and encrusted with 
ribosomes​
...
 

● Allows substances to 
exchange​ across 
membranes
...
Contains ribosomal 
RNA
...
 

● Carries out 
proteinsynthesis​
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Common in 
cells that secrete h
​ ormones 
and that m
​ etabolise​ ​lipids​
...
 

Rough Endoplasmic  Complex 3D system of 
Reticulum 
flattened sacs and 
membranes
...
 

with ​ribosomes​
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Cell-surface 
membrane 

Double​ membrane
...
 

● Regulates m
​ ovement​ of 
molecules in and out of 
cells
...
 

Mitochondria 

Double​ membrane
...
The ​matrix​ makes 
up the rest and contains its 
own DNA
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● Provides a large surface 
area for enzymic activity
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A Golgi vesicle is 
a small, spherical organelle 
bound by a ​single 
membrane​
...
 

● Involved in the ​synthesis 
and ​modification​ of 
biological molecules from 
the endoplasmic 
reticulum
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Chloroplasts 

Double​ membrane
...
Contains their own 
circular DNA
...
  

Cell Vacuole 

Contains ​cell​ ​sap​
...
 

● Maintains ​pressure​ inside 
the cell and keeps it turgid
...
 

Cell Wall 

Made of beta glucose 
(​cellulose​)
...
 

● The cell wall prevents the 
cell changing shape to 
withstand​ t​ he​ p
​ ressures​ ​of 
osmosis​
...
 
Lysosomes 

Type of ​Golgi​ v
​ esicle​
...
 

● Contains ​hydrolytic 
enzymes​ to break down 
unwanted organelles or 
material taken into the cell 
by p
​ hagocytosis​
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These cells contain ​no true nucleus, 
contain ​no membrane-bound organelles​ and are much​ smaller a
​ nd simpler than 
eukaryotic cells
...
 

Capsule 

Protects​ the cell and allows a
​ ttachment​ to other 
objects
...
 

Plasma 

Controls​ t​ he​ f​ low​ of small molecules in and out of 
the cell
...
 

Nuclear zone 

Contains the D
​ NA​ and RNA
...
 

Plasmids 

Circular​ ​DNA​ not associated with histones
...
 

What is the difference between eukaryotic and prokaryotic cells? 
 
Eukaryotic 

Prokaryotic 

Much bigger
...
 

Membrane-bound organelles
...
 

Contains a nucleus
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DNA associated with histones
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80s ribosomes (much bigger)
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DNA enclosed in a nucleolus
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Microscopy 

 
Optical Microscope - U
​ ses light and lenses to magnify images
...
Resolution is much lower as light has a much longer wavelength than electrons
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Scanning Electron Microscope - ​Directs a beam of electrons onto the surface of the 
specimen
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Specimens can be viewed in colour and 
3D
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Resolution is 20nm
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The resolution is 0
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The specimen must be 
extremely thin, there is a complex staining process for preparing a sample and living 
specimens cannot be viewed
...
 
 
 
 
 
 
 

Cell Fractionation and Ultracentrifugation  
Cell​ f​ ractionation​ is the process by which scientists break open cells to study and 
separate different organelles
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Cold - ​To reduce enzymic activity breaking down the organelles
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Buffered - ​To ensure that the pH does not fluctuate
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The cell is placed in a ​homogeniser​
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The resulting fluid (​homogenate​) is then filtered to remove 
debris
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This removes the 
most​ ​dense​ ​organelle​ (nucleus)
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● Nucleus (most dense/lowest speed)
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● ER
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Mitosis  
Mitosis i​ s important for growth, repair and reproduction, producing two genetically 
identical daughter cells
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The cell ​grows​ (G1), organelles are 
synthesised​ (S) and the DNA is 
checked for m
​ utation​ (G2)
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Rapid 
interphase suggests uncontrolled cell 
division
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The centrioles 
divide
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Sister chromatids are joined by a 
centromere​ and chromosomes ​move 
to the opposite p
​ oles​ of the cell
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Prophase 

Metaphase 

Image 

Each centriole is at an opposite pole
...
 
Each c
​ entromere​ is a
​ ttached​ to each 
pole​
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Chromatids 
are pulled to the poles (centromere 
first) and each half of the cell now has 
one chromatid
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Spindle fibres 
disintegrate and the nucleolus and 
nuclear envelope reform
...
Two ​genetically 
identical​ ​daughter​ ​cells​ are formed
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