Biology

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Prokaryotes	Small and Simple Bacteria DNA is not enclosed, one circular chromosome DNA is free, not attached to proteins Ribosomes no exterior membrane Lack of membrane-bound organelles Cell wall made up of peptidoglycan Binary fission (simplest form of cell division)
Cell Wall	-Protects and maintains the shape of the cell. -Composed of carbohydrate-protein complex called peptidoglycan. -Some bacteria have additional layer of polysaccharide outside the cell wall, this layer makes it possible for the bacteria to adhere to the structures such as teeth, skin and food.
Plasma Membrane	-Controls the movement of materials in and out the cell to a large extent -Plays role in binary fission -Cytoplasm occupied the complete interior of the cell -All cellular processes in prokaryotic cells occurs in the cytoplasm.
Pili	Used for attachment -Joining bacterial cells in preparation for the transfer of DNA from one cell to another (sexual reproduction) - Extensions from the bacterial cell body - Surface recognition
Flagella	-Allow the cell motility and propulsion -Extensions from the bacterial cell body -It can be used to sense certain chemicals and temperature.
Ribosome	-Site of protein synthesis -Very large numbers in cells with high protein production -They are smaller and less denser than those in the eukaryotic cells.
Nucleoid	- Non-compartmentalized and contains a single, long, continuos, circular thread of DNA -Cell control and reproduction Bacteria may also contain plasmids, this are small circular DNA molecules are not connected to the main bacterial chromosomes. The plasmid replicated independently of the chromosomal DNA -Plasmid DNA is not required by the cell under normal conditions but it may help the cell adapt to unusual circumstances.
Binary Fission	Very simple process called binary fission -The DNA is copied, the two daughter chromosomes becomes attached to different regions on the plasma membrane, and the cell divides into two genetically identical daughter cell -The division process includes an elongation of the cell and partitioning of newly produced DNA by microtubules-like fibres made of protein called FtsZ
Eukaryotes	Algae, Protozoa, Fungi, Plants and Animals
Nucleus	DNA resides. Bordered by double membrane (nuclear envelope) This provides an area where DNA can carry out its functions and not be affected by processes occurring in other parts of the cell. Does not provide complete isolation, (pores) allow communication.
Nucleolus	Dense, solid structure involved in ribosomes synthesis. It has numerous other functions including assembly of signal recognition particles, modification of transfer RNAs and sensing cellular stress.
Rough Endoplasmic Reticulum	Site of protein development and transport. Has ribosomes on the exterior of the channels. These proteins may become parts of membranes, enzymes, or even messengers between cells. The rough ER working with membrane bound ribosomes takes polypeptides and amino acids from the cytosol and continues protein assembly including, at an early stage, recognising a ‘destination label’ attached to each of them.
Smooth Endoplasmic Reticulum	Unique enzymes embedded on its surface. • Production of membrane phospholipids and cellular lipids. • Production of sex hormones (testosterone and oestrogen) • Detoxification of drugs in the liver • Storage of calcium ions needed for contraction in muscle cells. • Transportation if lipid-based compounds • To aid the liver in releasing glucose into the bloodstream when needed.
Golgi Apparatus	• Flattened sacs called cisternae, stacked on top of one another. • Collection, packing, modification and distribution of materials synthesised in the cell. • One side of the apparatus is near the rough ER, called cis side. It receives products from the ER. This products move into the cisternae. Movement then continues to the opposite side (trans side). Vesicles (small sacs) carry modified material to wherever they are needed inside or outside the cell. • Manufacture and secretes substances.
Centrioles	• Associated with nuclear division, • Composed of microtubules. • The area in which centrioles are found is called the centrosome. • Present in all eukaryotic cells, but are absent from higher plant cells. • Assembling microtubules, important to the cell in providing structure and allowing movement. • Microtubules are important for cell division.
Mitochondria	Rod shaped organelles, that appear throughout the cytoplasm. • Have their own DNA (autonomy within the cell) • Double membrane. Outer membrane is smooth, but inner membrane is folded into cristae • The cristae provide a hughe internal surface for the chemical reactions • Production of usable cellular energy called ATP (Adenosine triphosphate) • Produces and contains own ribosomes. • Carry out Respiration.
Lysosomes	Sacs bounded by a single membrane. • Contain and transport enzymes. • Usually absent from plant cells. • Intracellular digestive centres that arise from the Golgi apparatus. • Contains 40 different enzymes • Enzymes are hydrolytic and catalyse the breakdown of proteins, nucleic acid, lipids and carbohydrates. • Breakdown of material that may have brought into the cell by phagocytosis. • Interior of functioning lysosome is acidic. (enzymes hydrolyse large molecules)
Chloroplasts	• Only in algae and plant cell. • Contains double membrane. • Contains its own DNA and 70s ribosomes. (DNA form of a ring) • Interior includes grana, thylakoids, and stroma. • Grana (sing granum) made up of numerous thylakoids stacked like a pile of coins. Thylakoids are flattened membrane sacs with components necessary for the absorption of light. (first step in photosynthesis) • Fluid stroma, is similar to cytosol of the cell. Occurs outside the grana but within the double membrane. Storm contains enzymes and chemicals for the complete process of photosynthesis.
Ribosomes	Unique structures, do not have exterior membrane. • Carry out protein synthesis in the cell. • Found free in the cytoplasm or attached to the surface of the ER. • Always composed of a type of RNA and protein • Ribosomes of eukaryotic cells are larger and denser than those in the prokaryotic.

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