AQA AS Biology Unit 1: Structure of an Epithelial Cell

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  • Created on: 22-08-13 16:14
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Structure of an Epithelial Cell
Each cell can be regarded as a metabolic compartment, a separate place where the
chemical processes of that cell occur.
Cells are often designed to perform a particular function. Depending on that function, each
cell type has an internal structure that suits it for its job.
This is known as the ultrastructure of the cell.
Epithelial cells are eukaryotic cells.
Eukaryotic cells have a distinct nucleus and possess membrane-bounded organelles.
They differ from prokaryotic cells, such as bacteria.
Prokaryotic: a cell evolved before the nucleus
Eukaryotic: a cell evolved after the nucleus

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The Nucleus
The nucleus is the most prominent feature of a eukaryotic cell, such as an epithelial cell.
The nucleus contains the organism's hereditary material and controls the cell's
activities.
Usually spherical and between 10 and 20 µm in diameter, the nucleus has a number of
parts.…read more

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The Mitochondrion
Mitochondria are rod-shaped and 1-10 µm in length.
They are made up of the following structures:
Double Membrane
- Surrounds the organelle
- The outer membrane controlling the entry and exit of material
- The inner membrane is folded to form extensions known as cristae
Cristae
- Shell-like extensions of the inner membrane, some of which extend across the
whole width of the mitochondrion.…read more

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Endoplasmic Reticulum
The endoplasmic reticulum is an elaborate, three-dimensional system of sheet-like
membranes, spreading through the cytoplasm of the cells.
It is continuous with the outer nuclear membrane.
The membranes enclose flattened sacs called cisternae.…read more

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Golgi Apparatus
The Golgi apparatus occurs in almost all eukaryotic cells and is similar to the SER in structure
except that it is more compact.
It consists of a stack of membranes that make up flattened sacs, or cisternae,
with small rounded hollow structures called vesicles.
The proteins and lipids produced by the ER are passed through the Golgi apparatus in strict
sequence.
The Golgi modifies these proteins, often adding non-protein components, such as
carbohydrate, to them.…read more

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Lysosomes
Lysosomes are formed when the vesicles produced by the Golgi apparatus contain
enzymes such as proteases and lipases.
As many as 50 such enzymes may be contained in a single lysosome.
Up to 1.0 µm in diameter, lysosomes isolate these potentially harmful enzymes
from the rest of the cell before releasing them either to the outside or into a phagocytic
vesicle within the cell.…read more

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Ribosomes
Ribosomes are small cytoplasmic granules found in all cells.
They may occur in the cytoplasm or be associated with the RER.
There are two types, depending on the cells in which they are found:
80s type: found in eukaryotic cells, is around 25 nm in diameter
70s type: found in prokaryotic cells, is slightly smaller
Ribosomes have two subunits ­ one large and one small ­ each of which contains
ribosomal RNA and protein.…read more

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Microvilli
Microvilli are finger like projections of the epithelial cell that increase its surface
area to allow more efficient absorption.…read more

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Organelle Diagram Description Function
Plasma The membrane Regulates the
Membrane found on the movement of
surface of animal substances into
cells and just and out of the cell.
inside the cell wall Also has receptor
of plant cells and molecules on it,
prokaryotic cells. which allow it to
It's made mainly of respond to
lipids and protein. chemicals like
hormones.
Nucleus A large organelle Chromatin is made
surrounded by a from proteins and
nuclear envelope DNA. The pores
which contains allow substances
many pores.…read more

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Golgi A group of fluid- It processes and
Apparatus filled flattened packages new
sacs. lipids and proteins.
It also makes
lysosomes.
Lysosomes A round organelle Contains digestive
surrounded by a enzymes. These
membrane with no are kept separate
clear internal from the
structure. cytoplasm by the
surrounding
membrane, and
can be used to
digest invading
cells or to break
down worn out
components of the
cell.
Ribosomes A very small The site where
organelle that proteins are made.…read more

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