Transcript Cell structure

Unit 1
Cell and Molecular
Biology
Section 1
Cell Structure
Cells
Organisms can be divided into two major groups,
depending on the structure of their cells.
1.
Prokaryotes – bacteria and archaea
2.
Eukaryotes – Protists, fungi, animals and plants.
Prokaryotic Cell Structure
Organisms may be divided into two main forms :prokaryotic and eukaryotic
This is a typical prokaryotic bacterial cell and shows the following features
all of which are mentioned in the monograph P2
Plasmids
Structure
Definition
Nucleoid
This is highly condensed DNA in the form of a single
circular molecule. It is often referred to as a bacterial
chromosome
Plasmid
These are smaller rings of DNA which contain genes
Cytosol
This is the watery gel making up the majority of the
cell content and is the site of bacterial metabolism
Ribosomes
Bacteria have many ribosomes suspended in the
cytosol
Cell wall
Tough outer coat made of peptidoglycan (linked
dissacharide and peptide) and is used as the basis of
the gram stain
Capsule
The bacterial has a mucilaginous coating known as
the capsule Pili and Flagella – Both aid bacterial
movement
Eukaryotic animal cell
structure
Features common to all Eukaryotic cells
Plant and animal cells eukoryotic cells have a nucleus and other membrane bound
organelles. Common to both are :a) Cell membrane – controls entry and exit of molecules
b) Cystol – Fluid part of cytoplasm in which many reactions take place
c) Ribosomes – site of protein synthesis. These are bound to rough ER
d) Endomembrane system – various membrane bound organelles such as:

Nucleus – Contains genetic information e.g. DNA

Rough ER – Transport of proteins

Golgi – packages protein for secretion

Mitochondria – the sites of oxidative phosphorylation

Lysosomes – sub cellular digestion using powerful protease enzymes

Peroxisomes – breakdown of hydrogen peroxide

Cytoskeleton – System of fibres inside the cell which add strength, allow cell
movement

and allow cell to change shape
Features unique to animal Eukaryotes
Certain features are only found in animal cells e.g.
a)
Intermediate filaments – these are part of the cytoskeleton
which is discussed in more detail in the next section. These
filaments are found under the cell membrane and add
mechanical strength. Plant cell don’t need them as they have a
cell wall.
b)
Centrioles – These organise the spindle fibres during cell
division
c)
Microvili – the lack of a cell wall allows the animal cell to form
fold called micro-villi which further increase the surface area in
specialised cells e.g. epithelial cells of gut.
Features unique to plant Eukaryotes
Middle Lamellae This is the layer
between two
adjacent cells
Plasmodesmata
These are
cytoplasmic
connections
between plants
which all the
movement of
substances.
Cellulose Cell Wall –
Flexible, strong and elastic
wall which adds
mechanical strength and
prevent cell from bursting
Chloroplasts Synthesis of
carbohydrates using
light energy
Large permanent
vacuole - Contains cell
sap
Differences between Prokaryote and Eukaryote cells
Feature
Prokaryote
Eukaryote
Size
small, mean
diameter
0.5 - 5 m
Up to 40 m common
Genetic
material
Contained in
nucleoid and
plasmids
DNA associated with proteins to form a
chromosome, found within a nucleus
Organelles
Few present and
none surrounded
by a plasma
membrane
Many organelles;
Some with double membranes e.g. nucleus,
mitochondria and chloroplasts. Many with a single
membrane e.g. golgi apparatus, endoplasmic
reticulum and lysosomes
Cell Walls
Rigid formed from
glycoproteins
(mainly murein)
Fungi: Rigid, formed from polysaccharide chitin
Plants: Rigid, formed from polysaccharide
cellulose