Cells

Question 1

Eukaryotes (main characteristics)

Answer 1

Single celled OR multicellular, membrane bound nucleus and organelles, cell division via mitosis, 10-100μm

Question 2

Prokaryotes (main characteristics)

Answer 2

Unbound nucleoid and organelles, circular DNA, 0.2-2μm diameter, semirigid cell wall, no cytoskeleton, division via binary fission (archaea and bacteria)

Question 3

Phospholipids (main characteristics)

Answer 3

Amphipathic; hydrophilic phosphate-containing head bound to a glycerol molecule and a hydrophobic tail of 2 fatty acids.

Question 4

How do cell membranes maintain fluidity?

Answer 4

• lipid molecules may move laterally and rotate
• unsaturated fatty acid tails
• cholesterol as a “fluidity buffer”

Question 5

What are celll membranes MOST permeable to?

Answer 5

Small, hyrdophobic or neutral molecules (e.g. water, oxygen and carbondioxide)

Question 6

What are cell membranes LEAST permeable to?

Answer 6

Large molecules, ions and other polar molecules

Question 7

Explain the role of membrane proteins in the transport of molecules

Answer 7

“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

Question 8

Destinguish between hypertonic, hypotonic and isotonic

Answer 8

Hypertonic - area of low water concentration, hypotonic - high water concentration, isotonic - equal concentration

Question 9

Describe primary active transport

Answer 9

The movement of substances against the concentration gradient, thus involving the expenditure of metabolic energy, usually in the form of ATP.

Question 10

Provide an example of primary active transport

Answer 10

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.

Question 11

Describe secondary active transport

Answer 11

Transport that harnesses the diffusion of one substance down its concentration gradient to pump another substance against its conc. gradient

Question 12

Provide an example of secondary active transport

Answer 12

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

Question 13

Define: Symporter

Answer 13

A membrane protein that moves two solutes in the same direction (Na+/gyucose symport)

Question 14

Define: Antiporter

Answer 14

A membrane protein that moves two solutes in the opposite direction (ATPase antiporter)

Question 15

Define: Endocytosis

Answer 15

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)

Question 16

Define: Exocytosis

Answer 16

A form of vesicle mediated transport through which intracellular vesicles containing large particles fuse with the plasma membrane, depositing the contents outside the cell

Question 17

Define: Phagocytosis

Answer 17

Vesicle mediated inward transport of solids

Question 18

Define: Pinocytosis

Answer 18

Vesicle mediated inward transport of liquids

Question 19

What are the types of intercellular joints in animal cells

Answer 19

Tight (occluding) junctions, anchoring junctions and communicating (gap) junctions

Question 20

Describe tight (occluding) junctions

Answer 20

present between tightly associated adjacent cells, creating an impermeable barrier

Question 21

Describe anchoring junctions

Answer 21

Provide mechanical support of tissues via strong intercell adhesion (normally via desmosomes which are linked by cadherin)

Question 22

Describe communicating (gap) junctions

Answer 22

Specialised channels for chemical and electrical communication between adjacent cells

Question 23

Describe microfilaments

Answer 23

Fibres composed of actin that form a network within the plasma membrane to maintain cell shape

Question 24

Decribe microtubules

Answer 24

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

Question 25

Describe intermediate filaments

Answer 25

Primarily for cell structural support e.g. lamin is found in the nuclear envelope

Question 26

Describe carbohydrates

Answer 26

Exist as monosaccharides (e.g. glucose and fructose), disaccharides (e.g. sucrose) or polysaccharides (e.g. cellulose and starch)

Question 27

Describe lipids

Answer 27

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)

Question 28

Describe nucleotides

Answer 28

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)

Question 29

Describe nucleic acids

Answer 29

Strands of nucleotides joined by phosphodiester bonds. RNA is a single strand while DNA consisted of two hydrogen bonded anti-parallel strands

Question 30

Describe amino acids

Answer 30

The individual units that make up polypeptides. 13/22 can be synthesised by humans

Question 31

Describe polypeptides

Answer 31

Polypeptides are chains of amino acids joined by peptide bonds

Question 32

Describe proteins

Answer 32

Proteins are functional etities composed of 1 or more polypeptides

Question 33

Describe the primary (1) structure of proteins

Answer 33

The amino acid sequence of the polypeptide/s, determined by gene sequence.

Question 34

Describe the secondary (2) structure of proteins

Answer 34

The sturcture created by H-bonding between different different parts of the phospate backbone; forming a helices or b pleated sheets

Question 35

Describe the tertiary (3) structure of proteins

Answer 35

The interactions between different side-chains of the polypeptides; H-bonds, electrostatic interactions, disulphide bridges or hydrophobic interactions

Question 36

Describe the quaternary (4) structure of proteins

Answer 36

Two or more polypeptides coming together via H-bonds, electrostatic interactions, disulphide bridges or hydrophobic interactions

Question 37

Cell cycle: G1 phase

Answer 37

Follows mitosis (diploid); cell returns to normal functioning, may enter G0 phase where cell division is halted

Question 38

Cell cycle: S phase

Answer 38

“Synthesis” Phase, DNA is replicated - 46 duplicated chromosomes (diploid with chromosomes replicated)

Question 39

Cell cycle: G2

Answer 39

Cell increases in size and prepares for mitosis

Question 40

Cell cycle: M

Answer 40

Mitosis; PPMATC - the parent cell produces 2 identical diploid daughter cells

Question 41

Differentiate between cytokinesis in animal and plant cells

Answer 41

Animal - clevage furrow caused by an internal contractile ring composed of microfilaments
Plant - Vesicles deposit a new cell wall, internally dividing the parent cell

Question 42

Describe the Cell Control System

Answer 42

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?