2.3.1 Diagram of the eukaryotic liver cell.
2.3.2 Functions of the cell parts.
2.3.3 Electron micrographs of the liver cell.
2.3.4 Compare the prokaryotic and eukaryotic cell.
2.3.5 Three differences between a plant and an animal cell.
2.3.6 Outline two roles of extracellular components.
N:Nucleus
PM: plasma membrane
M: mitochondria
rER: Rough endoplasmic reticulum
GA: Golgi apparatus
L: Lysosome
MV: Microvilli
see 2.3.2 form functions of the cell components.
Nucleus: This is the largest of the organelles. The nucleus contains the chromosomes which during interphase are to be found the nucleolus.
The nucleus has a double membrane with pores(NP).
The nucleus controls the cells functions through the expression of genes.
Some cells are multi nucleated such as the muscle fibre
Plasma membrane: controls which substances can enter and exit a cell. It is a fluid structure that can radically change shape. see 2.4
The membrane is a double layer of water repellant molecules.
Receptors in the outer surface detect signals to the cell and relay these to the interior.
The membrane has pores that run from the cytoplasm to the surrounding fluid.
Mitochondria: location of aerobic respiration and the synthesis of ATP for
Double membrane organelle.
Inner membrane has folds called cristae. This is the site of oxidative phosphorylation.
Centre of the structure is called the matrix and is the location of the Krebs cycle.
Oxygen is consumed in the synthesis of ATP on the inner membrane
The more active a cell the greater the number of mitochondria.
Rough endoplasmic reticulum (rER): protein synthesis and packaging into vesicles.
rER form a network of tubules with a maze like structure.
In general these run away from the nucleus
The 'rough' on the reticulum is caused by the presence of ribosomes.
Proteins made here are secreted out of the cell
Ribosomes: the free ribosome produces proteins for internal use within the cell.
Golgi apparatus: modification of proteins prior to secretion.
proteins for secretion are modified
possible addition of carbohydrate or lipid components to protein
packaged into vesicles for secretion
Lysozyme:
Vesicles in the above diagram that form on the golgi apparatus.
Containing hydrolytic enzymes.
Functions include the digestion of old organelles, engulfed bacteria and viruses.
To identify structures within an electron micrograph it is necessary to know the scale at which the image has been taken. Look around the image to find the nucleus and then the mitochondria. In a plant cell there will also be the cell wall, chloroplasts and the vacuole to identify.
Nucleus:
In an electron micrograph the nucleus will be the largest of the organelles.
In this image there is a dark stained region celled the nucleolus which is the location of the DNA.
The membrane has pores which allow the entry of cell signal molecules, nucleotides and the exit of mRNA.
Generally the nucleus appears spherical however there are cells in which the nucleus has more unusual shape such as the multi-lobbed white blood cells.
Plasma membrane:
This image shows the junction between two liver cells. The image has been manipulated for clarity to see the two adjoining plasma membranes.
Notice the mitochondria to the left and the rER to the right of the membranes.
Mitochondria:
This micrograph of a mitochondria shows:
Double outer membrane
Folded inner membrane called the cristae.
Matrix of the mitochondria
These features are common to all mitochondria. Notice the rER above the mitochondria for scale and the dark granules of glycogen below the organelle.
Endoplasmic reticulum (rER).
The rER runs vertical in the image. Note the dark spots which are the ribosomes.
A cell with a great deal of rER is producing proteins for secretion outside of the cell.
The network of tubules allows proteins to be moved around within the cytoplasm before final packaging and secretion.
Golgi apparatus:
The golgi apparatus in the diagram forms a stack of membrane envelopes on top of each other.
Vesicles containing proteins fuse with the structure.
The proteins are modified inside the apparatus usually with the addition of non-protein substances.
Lysozyme:
simple membrane bound vesicle containing hydrolytic enzymes
produced in the golgi apparatus.
used to digest engulfed bacteria or viruses or old organelles
used to digest macromolecules
hydrolytic enzymes are retained within the vesicle membrane to prevent autodigestion of the cell.
Boston University Histology this site is a great source of histological diagram including those of the liver cell (syllabus specified).
Plant cell electron micrographs and images are provided at this stage although not specified at this point in the syllabus
Note the:
double membrane
internal thylakoid membranes which contain the chlorophyll.
Stroma where the calvin cycle fixes CO2 into carbohydrates, oils or starch.
Vacuole:
The vacuole is a storage area for organic solute such as sugars and amino acids.
The vacuole is surrounded by a membrane called the tonoplast which has essentially the same structure as the plasma membrane.
Cell Wall:
Plant cell walls are composed of cellulose (2.3.6)
In the electron micrograph we can see cytoplasmic connections through adjacent cells. These are called plasmodesmata.
a) Plant cell wall.
Found around all plant cells
Composed of cellulose.
Maintains the shape of the cell.
Provides structural support against the force of gravity.
prevents excessive uptake of water by the cell
b) Animal extracellular matrix
i) Basement membrane: a secretion formed from collagen and glycoproteins joined together by a third 'linkage' protein. Their exact composition varies form tissue to tissue.
Support: the membrane surrounds the tissues of lines ducts. It provides structural support for the integrity of the tissue or organ. Usually found as the basal lamina or basement membrane of epithelial cells.
Filter : The basement membrane of the kidney glomerulus provides the effective barrier for ultrafiltration
Vascular niche : Interestingly cells often require a base on which to organise before they will form proper tissue. There are implications here for developmental biology, tissue repair, stem cell therapies and cancer treatment.
ii) Interstitial matrix:
Bone has a matrix which includes collagen with a calcium phosphate.
Other tissues are surrounded by a matrix composed of a kind of gel that provides support for the tissue.
