Eukaryotic cell structure
• Function of cell organelles
• Function of cell structural components
• Differences between plant and animal cells
• Division of labour within a cell

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The eukaryotic cell structure is found in all plants, animals, fungi and protoctists
The complex structure allows for the specialisation of cells to perform certain functions
With the specialisation of function, cells can form tissues which can work together to form an organ
Hence eukaryotic cells can form complex multicellular organisms

The animal cell

Rough ER
Mitochondria
Ribosomes
Smooth ER
Vacuole
Nucleus
Lysosome

The plant cell

Eukaryotic cellular organelles and structure
The detailed organisation of the cell is called the cell ultrastructure
The ultrastructure of a cell can only be seen using an electron microscope
Organelles
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Nucleus
Mitochondria
Endoplasmic reticulum
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Ribosomes
Golgi body
Lysosomes
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Centrioles
Chloroplasts
Vacuole

Mitochondrion
Nuclear envelope
Nuclear pore
Nucleolus
Rough ER
Chromatin

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The nucleus controls the cells activities
It contains chromatin which are coils of DNA bound to protein. During cell division the chromatin condenses to form the chromosomes.
The nucleus is surrounded by a nuclear envelope
(double membrane) continuous with Rough ER.
Pores allow transport of mRNA and nucleotides from the nucleus to the cytoplasm.
The cytoplasm like material in the nucleus is called nucleoplasm
A region called the nucleolus synthesises ribosomes.

DNA and histone proteins form chromatin.
During cell division chromatin condenses to form visible chromosomes (prophase)

Mitochondria (pleural) mitochondrion (single) are sites isolated from the rest of the cytoplasm where enzymecatalysed reactions of respiration take place.
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Their main function is to synthesis ATP (adenosine tri-phosphate)
The organelle has a double unit membrane – the inner one being highly folded to increase surface area called the cristae.
The inner and outer membrane are separated by a narrow fluid filled inter membrane space
The interior of the mitochondria contains a fluid called the matrix
Some of the reactions of aerobic respiration takes place in the matrix while others on the inner membrane
Mitochondria have their own DNA (the genes code for respiratory enzymes)

Rough and smooth
Endoplasmic Reticulum
Golgi body
Rough endoplasmic reticulum
Transitional elements
Nucleus
Smooth Endoplasmic
Reticulum
Nuclear envelope

Rough ER
Rough and smooth
Endoplasmic Reticulum

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Rough and smooth
Endoplasmic Reticulum
There is a system of flattened membranes which form sacs in the cytoplasm of all eukaryotic cells called Endoplasmic Reticulum.
It is continuous with the nuclear membrane and can link to the Golgi body
It ’ s function is to transport substances throughout the cell
The fluid filled spaces between the membranes are called cisternae
ER encrusted with ribosomes is called Rough ER, whilst that devoid of ribosomes is smooth ER.
Smooth ER is concerned with lipid metabolism and the manufacture of steroids.
Rough ER transports proteins made by the ribosomes

Ribosomes

Ribosomes

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Ribosomes
These are the sites of protein synthesis within cells and are composed of ribosomal RNA and
protein.
Ribosomes are synthesised in a region of the nucleus called the nucleolus.
They can be attached to the ER or free-floating in eukaryotic cells but only free-floating in prokaryotic cells.
Attached ribosomes make proteins used outside the cell.
Free-floating ribosomes make protein for use inside the cell.

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Larger vesicles surrounded by a single unit membrane - formed from the Golgi body.
They contain hydrolytic enzymes (proteases and lipases) to digest the contents of food vacuoles with which they fuse. (Phagocytosis)
They can also fuse with and digest worn out cellular organelles. The entire cell can be destroyed on occasions when the lysosomes break down ( suicide bags ).

Centrioles
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Centrioles are found in all animal cells, protoctists but not in higher plants .
They are found outside the nucleus in a region of the cytoplasm called the centrosome.
These have a 9 + 2 microtubular arrangement when viewed in cross-section.
They consist of two hollow cylinders positioned at right angles to each other.
They are the regions from which the spindle fibres emerge during cell division. Centrioles migrate to opposite ends of the nucleus and molecules of tubulin (a dimer protein with a large molecular weight) polymerise to form the spindle.

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Chloroplast (Plants only)
Sites isolated from the rest of the cytoplasm in
eukaryotic plant cells where reactions of photosynthesis occur.
They consist of a double membrane with a fluid filled stroma.
The stroma contains ribosomes, lipid, circular DNA and starch
The thylakoids (stack of pennies) form the granum and house the photosynthetic pigments
The thylakoids are adapted to form a large surface area to trap light
Main function is to manufacture reduced nicotinamide adenine dinucleotide phosphate (NADP.H
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) and ATP in the light dependent reactions, to use in the light independent reactions to fix CO carbohydrate (Starch).
2 into a storage

Permanent Vacuole

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Permanent Vacuole
These include numerous small vesicles found in animal cells (food vacuoles) and a large central cavity surrounded by a single membrane called
the tonoplast, in plant cells.
In animal cells vacuoles are a temporary store of food and secretions
In plants the permanent vacuole is a store of amino acids, carbohydrates and lipids (mainly oils). They also store tannins and other substances that comprise cell sap.
The cell sap provides an osmotic system which plants can alter to move water in and out

These are the structural elements of the cell required for protection, shape, boundary layers and movement
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Cellulose cell wall
Cytoskeleton
Flagella and cilia
Plasma membrane
Cytoplasm

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The cell wall consists of cellulose microfibrils embedded in a polysaccharide matrix.
The cell wall provides strength and support and also permits the movement of water from cell to cell via the plasmodesmata.

There are gaps in the cell wall that allow neighbouring cells to link together
There is a continuation of
cytoplasm
from cell to cell and the
endoplasmic reticulum can also be
linked

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The cytoskeleton is an internal network of protein fibres which helps to keep the cell shape.
There are three types:
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The actin filaments are able to move against each other and can cause the cell to move (WBC) or move organelles around
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Intermediate filaments help provide structure
Microtubules are cylinders made from a protein called tubulin. Microtubule motors on the tubulin use ATP for movement
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Move chromosomes during mitosis
Move vesicles from ER to golgi body

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Both have the same structure but cilia are shorter and tend to occur in greater numbers
(flagella 1-2)
Flagella also tend to move the entire cell (sperm) cilia tend to ‘ sweep ’ substances and mucus
Each consists of a cylinder with a 9 + 2 arrangement of microtubules which use
ATP as a source of energy

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Function of the plasma membranes:
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Occur around the cell and determine what enters and leaves the cell
Occur around organelles isolating enzymes within the organelle
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Within organelles providing a large surface area for the attachment of enzymes
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Provide a transport system within the cell. e.g vesicles
The structure of the plasma cell membrane will be studied in section 1.3

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The cytoplasm outside the organelles is called the cytosol
The cytosol is a complex mixture of cytoskeleton filaments, dissolved molecules, and water that fills much of the volume of a cell.
The cytosol is the site of glycolysis
(respiration)

ANIMAL CELL PLANT CELL
Courtesy of Dr. Julian
Thorpe – EM & FACS Lab,
Biological Sciences
University Of Sussex

Plant and animal cells are eukaryotic cells
Both types of cell possess characteristic organelles;
• Nucleus
• Rough endoplasmic reticulum
• Smooth endoplasmic reticulum
• Mitochondria
• Golgi apparatus
• Microtubules
Differences between mature plant and animal cells include:
PLANT CELLS
• Cellulose cell wall
•
ANIMAL CELLS
Microvilli
• Large vacuoles that store cell sap
• Centrioles
• Chloroplasts in photosynthetic cells

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The relationship between organelles
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The DNA in the nucleus contains the code to produce the protein. A gene on the DNA will be copied
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The code will be ‘ transcibed ’ by mRNA
The mRNA attaches to the ribosome (free or on RER)
The protein will be made using tRNA
The assembled protein inside the RER will be pinched off into a vesicle and transported to the golgi body
The golgi will package the protein and maybe modify
Another vesicle will be pinched off the golgi and moved to cell surface for exocytosis

Division of labour
How organelles work together