CELLS Flashcards
Electron microscope
-Uses electrons rather than light to produce images
-The electron microscope can magnify much more than a light microscope as electrons have a shorter wavelength than light
Resolution
The ability to see two adjacent points as distinct entities following magnification
TEM
-Transmission electron microscope
-Electrons passing through a very thin specimen, produces very high quality images
SEM
-Scanning electron microscope
-Electrons reflecting off the surface of the image as opposed to going through it
-Resolution and maginifcation are not as high but it gives a 3D image
Eukaryotic cells
-Found in animals, plants and fungi
Mesosome
Tightly folded region of the cell membrane containing all the membrane-bound proteins required for respiration and photosynthesis
Flagellum
Rigid rotating helical-shaped tail used for propulsion
Cell membrane
-Two layers of phospholipids (bilayer)
-hydrophillic heads facing out, hydrophobic tails facing in
Function of the hydrophobic centre of the phospholipid bilayer
Prevents the free diffusion of water and polar molecules through the membrane
Structure of the plasma membrane
-Phospholipid bilayers
-Intrinsic and extrinsic proteins
-Carbohydrate glycocalyx
-Glycoproteins
-Glycolipids
-Cholesterol
arranged in a fluid mosaic structure
Proteins in the cell membrane
-Help provide stability and support as they ‘anchor’ the phospholipid molecules
-May act as enzymes
-Some act as adhesion sites, where adjacent cells are held together
-Involved in cell recognition and as receptors or antigens
-Particularly important in transporting substances across the bilayer
Advantages to having enzymes in the membrane
-Kept in the ideal place in terms of substrate availabiity and pH
-Need replaced less often
Examples of enzymes in the membrane
-In the membrane of the small intestine which are important in the digestion of disaccharides
Channel proteins
-Span the membrane and work by creating a hydrophillic channel that allows polar molecules to bypass the hydrophobic centre of the bilayer
-May be permenantly open or have their opening controlled (gated)
-Gated channels are very important in controlling the passage of ionsinto and out of neurons during nervous conduction
Carrier proteins
-Carry specific ions and molecules across the membrane
-May be because the ions have charged groups, or because the molcules have to be moved across the concentration gradient
-Can change shape to carry the substance from one isde of the membrane to the other
Factors that affect membrane fluidity
-The more phospholipids with sunsaturated hydrocarbon chains there are, the more fluid the membrane is (kinks prevent them from packing close together)
-Phospholipids with longer hydrocarbon chains will decrease the fluidity since attractive forces among the chains will be greater
-Cholesterol acts as a temperature stability buffer, at high temperatures it provides additional binding forces so decreases membrane fluidity, and at low temperatures prvents the phospholipids from packing too close together and ‘freezing’
Nucleus
-Controls the cells acivities as it contains the genetic informatio in the form of chromosonal DNA (which codes for protein synthesis in the cytopasm)
-Surrounded by a nuclear envelope
-Envelope is perforated with nuclear pores which allow for exchange of substances between the nucleus and cytoplasm
-Outer membrane of the envelops is encrusted with ribosomes and is the site of the RER
-The nucleoplasm contains chromatin and one or more nucleoli
-Chromatin is mainly coils of DNA called chromosones bound to basic proteins called histones
-Heterochromatin is tightly coiled chromatin therefore stains darker
-the loossely coiled chromatin is called euchromatin and are thought to contains the DNA which is active during interphase
-The nucleolus is a rounded structure whose function is the manufacture of ribosomal RNA and ribosomes, and stains intensely because it contains lots of DNA and RNA
The endoplasmic reticulum
-Joined to the outer surface of the nuclear membrane
-Consists of flattened, membrane-bound sacs caled cisternae
-These may be covered with ribosomes forming rough ER whihc is flattened, or ribosomes may be absent, forming smooth ER which is usually more tubular
-Both are concerned with the synthesis and transport of substances
Rough ER protein synthesis
-The growing polypeptide chain is bound to the ribosome until it’s synthesis is complete, ribosome is attached to the ER
-The protein passes through a channel into the cisternae of the ER
-Once inside, the proteins folds into it’s tertiary structure thus trapping it inside the ER
-The protein is now transported through the cisternae and is modified as it moves through
-The protein then travels to the golgi aparatus
-From here it is secreted from the cell or passed to other organelles in the cell
Functions of the smooth ER
Lipid synthesis, metabolism and cholesterol synthesis
Ribosomes
-Very small organelles found in large numbers in the cytoplasm
-Two types (70S and 80S)
-70S is found in prokaryotes and the 80S are found in eukaryotes
-Made of ribosomal RNA and protein
-During protein synthesis, at ribosomes amino acids are joined together one by one to form polypeptide chains
-Acts as a binding site for protein synthesis
Golgi apparatus
-Consists of a stack of flattened, membrance-bound sacs called cisternae together with golgi vesicles in a system of interconnected tubules formed around a central stack
-At the convex forming face, new cisternae are constantly being formed by fusion of vesicles which are derived from the buds of the ER
-The maturing face is concave and this is where vesicles pinch off the cisternae again
The whols stack is made up of cisternae moving from the forming to the maturing face
Function of the golgi apparatus
-Transport and modify proteins
–Protein received by the golgi from the ER have short carbohydate chains added to them to become glycoproteins
-Proteins are then packaged into vesicles either for secretion from the cell by exocytosis or for delivery to somewhere else in the cell
-Also secretes some carbohydatres and lipids
-Formation of lysosomes
Vesicles
-Small organelles which are pinched off the maturing face of the golgi
-Bounded by a single membrane
-Used for storage or transport of substances to and from the cell surface membrane
Vacuoles
-Large permenant vacuoles are found in plant and fungal cells
-Bound by a single membrane
-Small temporary vacuoles are in animal cells
-The membrane of the sap vacuole in plants is called the tonoplast
-Used for storage of water and ions
Lysosomes
-Found in most eukaryotic cells, particularly animal cells
-Vesicles produced by the golgi which contain hydrolytic enzymes
-These enzymes are made on thr rough ER and transported to the golgi apparatus
-Golgi vesicles containing the enzymes later bud off from the golgi and are called primary lysosomes
Functions of lysosomes
-Digestion of material taken in by endocytosis, the lysosome fuses with an endocytotic vesicle to form a secondary lysosome, releasing enzymes into it to digest it
-Digestion of old/non-functioning organelles (autophagy), lysosome fuses with the membrane-bound organelle releasing enzymes into it
-Breakdown of the whole cell (autolysis), contents of the lysosome release into the cytoplasm causing digestion of the cell
Microtubules
-Nearly all eukaryotic cells contain these
-Very fine tubes made up of the protein tubulin
-Found in the centrioles and throughout the cytoplasm of animal and fungal cells, and are involved in a number of cell processes
Microtubules funtion in cell division
Centroiles form the spindle fibres during cell division of animal and fungal cells
-At the beginning of cell division the cells replicate and the two new pairs move to oppoite sides of the cell spindle
-The microtubules control the separation of chromatids or chromosones during cell division, and enable the movement of these structures within the cell
Plasmodesmata
-Living connections that pass between neighbouring plant cells through very fine pores in adjacent cell walls
-Enables a continuous system of protoplasm to be formed between neighbouring cells for transport of substances between cells
Prokaryotic cells
-Usually small
-Single, circular DNA molecule without associated protein. the region in the cytoplasm containing the DNA is called the nucleoid
-Ribosomes are small 70s structures
-Peptidoglycan cell wall
-No microtubules
-No membrane bound organelles
Eukaryotic cells
-Usually large
-DNA as several lonear molecules with associated protein called histone to form chromosones. DNA in membrane-bound nucleus
-Ribosomes are larger 80s structures
-Asexual division by mitosis
-Cellulose cell wal in plant cells, chitin cell wall in fungal cells
-Microtubules present and organised into centrioles in animal cells
Has a nucleus mitochondria, chloroplasts, endoplasmic reticulum, golgi complex, vesicles, lysosomes and microtubules
Glycocalyx layer
-The polysaccharides that bin o membrane protein or phospholipid are always found on the outside of the cell surface membrane and are always peripheral to the protein or phospholipid.
-Glycoproteins/lipids are involved in cell-to-cell recognition and some glyoproteins can act as antigens or receptor sites (provide sites on the cell surface membrane that particuar molecules fit.
-As glyoproteins and lipids can form hydrogen bonds with water molecules outside the membrane, they help stabilise the membrane
Mitchondria structure and function
-Enclosed within a double membrane separated by an inner-membrane space
-The inner membrane is extended to form cristae that extend into the matrix of the mitochondrion
-The infolding gives the inner mitochondrial membrane a greater surface area, therefore increasing the amunt of enzymes that can be embedded within the membrane
-The site of ATP synthesis during aerobic respiration
-Cristae tend to be more numerous and more deeply folded in highly active cells
Chloroplasts structure and function
-Bound by a double membrane or envelope which encloses the stroma, which within contain thylakoids
-At intervals, thylakoids are stacked into grana and the space between the grana are referred to as inter-grana
-Usually have one or more starch grains and smaller lipid droplets
-Chloroplasts are the site of photosynthesis and are located in the palisade layer of leaves
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