Cells Flashcards
Eukaryotes (main characteristics)
Single celled OR multicellular, membrane bound nucleus and organelles, cell division via mitosis, 10-100μm
Prokaryotes (main characteristics)
Unbound nucleoid and organelles, circular DNA, 0.2-2μm diameter, semirigid cell wall, no cytoskeleton, division via binary fission (archaea and bacteria)
Phospholipids (main characteristics)
Amphipathic; hydrophilic phosphate-containing head bound to a glycerol molecule and a hydrophobic tail of 2 fatty acids.
How do cell membranes maintain fluidity?
- lipid molecules may move laterally and rotate
- unsaturated fatty acid tails
- cholesterol as a “fluidity buffer”
What are celll membranes MOST permeable to?
Small, hyrdophobic or neutral molecules (e.g. water, oxygen and carbondioxide)
What are cell membranes LEAST permeable to?
Large molecules, ions and other polar molecules
Explain the role of membrane proteins in the transport of molecules
“Facilitated Diffusion” utilises the concentration gradient - CARRIER PROTEINS bind to a solute, undergo a conformational change moving the solute to the other side of membrane. CHANNEL PROTEINS act as pipes for direct passage of solutes
Destinguish between hypertonic, hypotonic and isotonic
Hypertonic - area of low water concentration, hypotonic - high water concentration, isotonic - equal concentration
Describe primary active transport
The movement of substances against the concentration gradient, thus involving the expenditure of metabolic energy, usually in the form of ATP.
Provide an example of primary active transport
Antiporters known as ATPases (or “ion pumps”) use ATP to pump 3 Na+ ions out of the cell and 2 K+ ions into the cell, creating an electrochemical gradient.
Describe secondary active transport
Transport that harnesses the diffusion of one substance down its concentration gradient to pump another substance against its conc. gradient
Provide an example of secondary active transport
The Na+/glucose symporter uses the Na+ gradient created by ATPase to co-transport glucose into the cell as Na+ moves back down the electrochemical gradient
Define: Symporter
A membrane protein that moves two solutes in the same direction (Na+/gyucose symport)
Define: Antiporter
A membrane protein that moves two solutes in the opposite direction (ATPase antiporter)
Define: Endocytosis
A form of vesicle mediated transport through which an area of membrane enfolds, forming a vesicle around a large particle for transport into the cell (phagocytosis/pinocytosis)
Define: Exocytosis
A form of vesicle mediated transport through which intracellular vesicles containing large particles fuse with the plasma membrane, depositing the contents outside the cell
Define: Phagocytosis
Vesicle mediated inward transport of solids
Define: Pinocytosis
Vesicle mediated inward transport of liquids
What are the types of intercellular joints in animal cells
Tight (occluding) junctions, anchoring junctions and communicating (gap) junctions
Describe tight (occluding) junctions
present between tightly associated adjacent cells, creating an impermeable barrier
Describe anchoring junctions
Provide mechanical support of tissues via strong intercell adhesion (normally via desmosomes which are linked by cadherin)
Describe communicating (gap) junctions
Specialised channels for chemical and electrical communication between adjacent cells
Describe microfilaments
Fibres composed of actin that form a network within the plasma membrane to maintain cell shape
Decribe microtubules
Hollow cylinder structures composed of tubulin that provide tracks for organelle movement, assist in mitosis and allow whole cell movement by forming cilia and flagella
Describe intermediate filaments
Primarily for cell structural support e.g. lamin is found in the nuclear envelope
Describe carbohydrates
Exist as monosaccharides (e.g. glucose and fructose), disaccharides (e.g. sucrose) or polysaccharides (e.g. cellulose and starch)
Describe lipids
Exist as simple lipids (alcohol + fatty acid), fats (1 glycerol molecule + 3 fatty acids), phospholipids (2 fatty acids, 1 glycerol molecule + phosphate-containing head), waxes - (fatty acids + functional groups) or steroids (covalently linked rings with differing functional groups)
Describe nucleotides
The individual units of nucleic acids, consisting of phosphate, pentose (ribose in RNA and deoxyribose in DNA) and a nitrogenous base (adenine, cytosine, guanine, thymine or uracel)
Describe nucleic acids
Strands of nucleotides joined by phosphodiester bonds. RNA is a single strand while DNA consisted of two hydrogen bonded anti-parallel strands
Describe amino acids
The individual units that make up polypeptides. 13/22 can be synthesised by humans
Describe polypeptides
Polypeptides are chains of amino acids joined by peptide bonds
Describe proteins
Proteins are functional etities composed of 1 or more polypeptides
Describe the primary (1) structure of proteins
The amino acid sequence of the polypeptide/s, determined by gene sequence.
Describe the secondary (2) structure of proteins
The sturcture created by H-bonding between different different parts of the phospate backbone; forming a helices or b pleated sheets
Describe the tertiary (3) structure of proteins
The interactions between different side-chains of the polypeptides; H-bonds, electrostatic interactions, disulphide bridges or hydrophobic interactions
Describe the quaternary (4) structure of proteins
Two or more polypeptides coming together via H-bonds, electrostatic interactions, disulphide bridges or hydrophobic interactions
Cell cycle: G1 phase
Follows mitosis (diploid); cell returns to normal functioning, may enter G0 phase where cell division is halted
Cell cycle: S phase
“Synthesis” Phase, DNA is replicated - 46 duplicated chromosomes (diploid with chromosomes replicated)
Cell cycle: G2
Cell increases in size and prepares for mitosis
Cell cycle: M
Mitosis; PPMATC - the parent cell produces 2 identical diploid daughter cells
Differentiate between cytokinesis in animal and plant cells
Animal - clevage furrow caused by an internal contractile ring composed of microfilaments
Plant - Vesicles deposit a new cell wall, internally dividing the parent cell
Describe the Cell Control System
3 checkpoints that ensure efficient reproduction. C1 - exiting G0 phase; is cell division required? C2 - exiting G2 phase; is the DNA replicated correctly and undamaged? C3 - between Meta and Ana; are the splindles correctly attached to the centromeres?
