BIOLOGY 11/12
CELLULAR STRUCTURES AND THEIR FUNCTIONS
*NOTE: ORGANELLES ARE STRUCTURES THAT ARE ENCLOSED IN A DOUBLE
MEMBRANE THAT IS SIMILAR TO THE CELL MEMBRANE.
Cell membrane:- also known as the plasma membrane
-holds the contents of the cell; helps the cell maintain its shape
-separates the cell’s contents from the environment
-helps to maintain homeostasis by regulating the movement of material into and out
of the cell
-is selectively permeable because it only allows certain molecules in at certain times
-our understanding of the plasma membrane is based on the fluid mosaic model
-“fluid” because the molecules which form it are able to move around within
the membrane
-“mosaic” because it is made of different types of organic molecules such as
phospholipids, proteins, and polysaccharides (carbohydrates)
Cytoplasm: -a fluid that contains water and dissolved substances
-gives shape to the cell and fills out the cell membrane
-many chemical reactions take place here such as synthesis of fats, synthesis of
proteins, and anaerobic cellular respiration
-organelles are thought of as being suspended in the cytoplasm
Nucleus: -controls the cell’s metabolism (i.e. all the chemical reactions that occur within the
cell)
-holds chromosomes which are the structures that contain the cell’s genetic
information; they are the “blueprints” of life
-when stretched out, called chromatin
-made of a chemical called deoxyribonucleic acid (DNA)
-each member of a species has the same number of and types of
chromosomes
Nuclear membrane: -also known as the nuclear envelope
-similar in structure to the cell membrane
-has pores to control the movement of soluble materials into and out of the nucleus
Nucleolus: -site of the synthesis of ribosomes
-usually seen as darkly stained areas of the nucleus
Ribosome: -made of ribonucleic acid (RNA)
-involved in the synthesis of protein
-proteins include enzymes (to speed up chemical reactions), hormones and
pheromones (chemical messengers), receptors of chemical signals,
transportation channels, chemical signals on membrane surfaces, pigments
(coloured chemicals), and structural elements
-actually “holds” the chemical instructions for making the protein (messenger RNA
or mRNA)
-can be found free-floating in the cytoplasm (clusters of these ribosomes are called
polysomes)
-proteins made here are for use inside the cell
-can be attached to the endoplasmic reticulum
-proteins made here are for export from the cell
Endoplasmic reticulum:- also known as ER
-a system of tubules that is made of double membranes
-used as an assembly line and transportation system
-smooth ER is the site of lipid synthesis and is involved in the detoxification of
drugs and other harmful chemicals
-rough ER has ribosomes attached to it making it appear “rough”
-also packages and modifies the proteins produced by the attached ribosomes
Golgi Body: -also known as Golgi Apparatus or Golgi Complex
-connected to the ER
-modifies and packages the proteins produced by the cell for export (secretory
proteins)
-these packages of material are known as vesicles
-synthesises complex polysaccharides
Mitochondrion: -plural form = mitochondria
-site of the reaction in aerobic cellular respiration
-has its own DNA and is capable of synthesising some but not all of its own proteins
-suggests that mitochondria were once independent life forms
Vacuoles: -sacs which temporarily store food, water, waste, or proteins
-in plants, large central vacuole helps to put pressure on the cell wall to help it
maintain its shape and rigidity
-in some freshwater single-celled organisms, a contractile vacuole is necessary to
store and pump out excess water
Lysosome: -sac that contains digestive enzymes to break down fats, carbohydrates and
proteins into their building blocks so that they can be used by the cell
-fuses with food vacuoles to form digestive vacuoles
-involved in the recycling of dead cells
-burst and digest the contents of the whole cell
-called the “suicide bag”
Microtubule: -protein fibre that makes up the cell skeleton (cytoskeleton)
-gives shape to the cell
-forms the cilia (short, hair-like structures found around the whole cell) and the
flagella (long, whip-like structures usually found at the ends of the cell)
-forms the spindle in mitosis
Microfilament: -protein fibre that is different in structure from the microtubules
-influences changes in cell shape and involved in cytoplasmic streaming (the
characteristic cyclic motion of the cytoplasm in plant cells)
Plastids:- have a variety of functions
-only found in plant cells
-e.g. chloroplasts
-most important plastids
-contain a green pigment called chlorophyll
-site of photosynthesis
-like mitochondria, have own DNA and may once have been
independent organisms
-e.g. chromoplasts
-store/contain pigments
-e.g. amyloplasts/leucoplasts
-store starch
Cell Wall: -found only in plants, bacteria, some protists, and some fungi
-non-living part of cell
-usually made of cellulose
-provides a rigid structure and supports the cell
Centrioles: -found only in animal cells
-produce the spindle in mitosis (cell division)
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