cellular components + functions notes

AS level Biology A OCR spec

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cellular component Outline of their functions
nucleus Contains the DNA. This DNA controls the synthesis of all the proteins required by the
cell (the actual synthesis does not occur in the nucleus). Example: metabolic activities
nucleolus An area within the nucleus responsible for producing ribosomes. It is composed of
proteins and RNA which is used to produce rRNA to form the ribosomes needed for
protein synthesis
nuclear envelope This is the double membrane which contains the DNA. This protects it from being
damaged in the cytoplasm. This envelope has nuclear pores allowing molecules to move
in and out of the nucleus. Ex: the RNA molecules which are copies of DNA leave the
nucleus this way, as DNA molecules are too big to exit through the pores.
RER and SER ER is connected to the outer membrane of the nucleus and is a network of membranes
which contain sacs called cisternae.
SER- responsible for lipid and carbohydrate synthesis and storage.
RER- responsible for synthesis and transport of proteins. Has ribosomes bound to its
surface.
Cells that release hormones or proteins have more RER.
Ribosomes Can be free in the cytoplasm, or attached to ER which makes RER. They are NOT
membrane-bound. They are made of RNA molecules created in the nucleolus of the
cell.
Site of protein synthesis. Mitochondria and chloroplasts contain ribosomes.
Golgi apparatus Similar structure as the SER. It is a compact structure made of cisternae and does NOT
contain ribosomes.
Role: modifying and packaging proteins into vesicles.
Mitochondria The final site of cellular respiration ­ they produce ATP (a molecule) which makes the
(Mitochondrion ­ energy stored in the bonds of complex organic molecules available for the cell to use.
singular) The number of mitochondria in a cell is dependent on the amount of energy it uses.
Mitochondria has a double membrane, the inner membrane is folded a lot and is called
cristae. The inside of mitochondria is fluid and called the matrix.
Mitochondria contain a small amount of DNA and they can produce their own enzymes
and reproduce themselves.
Vesicles They are membranous sacs that have a single membrane with a fluid inside. They
transport materials inside the cell. Also have storage rolls.
2.4 Eukaryotic Cell Structure, 2.5 The Ultrastructure of Plant Cells

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Lysosomes These are specialised forms of vesicles that contain hydrolytic enzymes. They break
down waste material inside cells (including old organelles), also break down pathogens.
Play a role in programmed cell death.
Centrioles A component of the cytoskeleton, present in most eukaryotic cells except fungi
Composed of microtubules. Two centrioles form a centrosome which is involved in the
organisation of spindle fibres during cell division.
flagella An extension that protrudes from the cell. Longer than cilia.
(flagellum-singular) Their function is mostly to enable cell motility.…read more

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