Cell biology 1.1-1.5

Question 1

What are the principles of cell theory?

Answer 1

> all organisms are made of cells 
> cells have membranes 	
	- division 
> cells conduct metabolic processes 
> cells have their own energy and genetic material

Question 2

Exceptions to cell theory

Answer 2

• striated muscle cell
  
  • multinuclear fusion of many cells
• cells formed without cytokinesis
  
  • giant algae

Question 3

What are the functions of a unicellular organism?

Answer 3

• homeostasis
• metabolism
• reproduction (of genetic material)
• growth
• nutrition
• excretion
• reaction / response
• in multicellular organisms different cells have different functions (differentiation)

Question 4

Why is surface area to volume ratio important?

Answer 4

• volume = amount of cytoplasm and metabolism
• surface area = exchange of materials
• larger cells need more surface area → more metabolism
  
  • too small ratio → not enough secretion → overheating

Solutions
- microvilli 
	- creating extensions 
- flattening into thin film 
- dividing cytoplasm into smaller parts

Question 5

What are emergent properties?

Answer 5

• sharing functions between different cells (and compartments within a cell)
• more than sum of the properties

Question 6

How do cell specialise?

Answer 6

> differentiation 
	- the same genetic material 
	- gene expression 
> more effective 
	- same function groups = tissue

Question 7

Stem cells

Answer 7

> capable of renewing for long time
> variable potency (differentiation)
> embryonic 
	- unlimited growth potential 
	- high tumour risk 
	- ethical considerations 
> cord blood 
	- easily obtained and stored 
	- compatible with adult body 
	- limited amount 
> adult 
	- limited potency 
	- compatible with tissue 
	- difficult to obtain

Question 8

Therapeutic uses of stem cells

Answer 8

• Stargardt’s disease
  
  • active transport in retina cells
  • retina degenerates
  • no light detection
  • stem cells in retina
• Leukemia
  
  • abnormally reproducing WBC
  • stem cells frozen
  • chemotherapy
  • stem cells reintroduced

Question 9

What is the structure of prokaryotic cell?

Answer 9

• simplest structure
• no nucleus
  
  • lighter
  • DNA
• one chamber
• ribosomes 70s

Question 10

What is binary fission?

Answer 10

• cell division of prokaryotes
  
  • DNA replication
  • opposite ends of the cell
  • membrane elongates (cytokinesis)

Question 11

How can cell perform many functions simultaneously?

Answer 11

• made of compartments
  
  • higher concentration of enzymes and substances
  • different pH
  • compartments move
    
    • protection from dangerous enzymes
• nucleus has chromosomes

Question 12

What are the amphipathic properties?

Answer 12

• hydrophobic parts
  
  • phospholipid tails
• hydrophilic parts
  
  • phospholipid heads
  • phosphate group
    > arranged in double layer
  • hydrophilic parts on the outside

Question 13

What were different phospholipid bilayer models?

Answer 13

Davson-Danielli model
     - phospholipids sandwiched between protein layers 
     - good barrier 

Singer and Nicolson model (fluid mosaic) 
     - proteins have different positions 
     - peripheral, integral proteins
     - phospholipids and proteins move

Question 14

How was Davison-Danieli falsified?

Answer 14

> freezing of cells and fracturing them 
	- globular structures appeared - transmembrane proteins 
> structure of membrane proteins 
	- globular, different shapes 
> fluorescent tagging 
	- antibodies on proteins 
	- scattered = movement

Question 15

What are the functions of membrane proteins?

Answer 15

• hormone receptors
• immobilised enzymes
  
  • active site outside
• cell adhesion
  
  • junctions in tissue
• cell-to cell communication
  
  • synapses
• channels for passive transport
• pumps for active transport

Question 16

What is cholesterol and what is its role?

Answer 16

• in animals
• hydrophobic
• near neurotransmitters
• role in membranes
  
  • stabilising
    
    • disrupt tails = no cristalisation
    • disrupts molecular motion = no liquid

Question 17

What is simple diffusion?

Answer 17

• particles move from high concentration to low
  
  • gases
  • solutes in solvent
• no energy

Question 18

What does semi-permeability mean?

Answer 18

• only some particles can move through
• plasma membrane
  
  • only small and uncharged molecules pass
    
    • water, O2, CO2, urea

Question 19

What affects diffusion rate?

Answer 19

• concentration gradient
• surface area
• length of diffusion

Question 20

Increase in diffusion rate

Answer 20

> surface area 
	- villi
	- cristae in mitochondrion 
	- alveoli 
> diffusion distance 
	- thin membrane 
	- single layer of cells 
	- small diameter

Question 21

What is osmosis?

Answer 21

• movement of solvent molecules
• semi-permeable membrane necessary
• types of solutions
  
  • hypertonic (high solute)
  • isotonic (equal)
  • hypotonic (low solute)
• osmolarity - total concentration of osmotically active solutes

Question 22

What is facilitated diffusion?

Answer 22

• molecules that are too big or charged cannot pass
  
  • glucose
  • ions
• protein transporters (glucose) or channels (channels)
• along conc. gradient
  - no energy needed

Question 23

How does potassium channel work?

Answer 23

• 4 protein subunit
• pore small
  
  • potassium solution can’t pass
  • potassium broken into ions passes
  • other molecules can’t pass
• impulse (nerve cells)
  
  • charges change
    
    • outside (-) inside (+) —> normally the other way
  • channel opens and close rapidly
    
    • ball goes into the pore

Question 24

What is active transport?

Answer 24

• through pump
• needs energy (ATP)
• against gradient

Question 25

How does a pump work?

Answer 25

> nerve impulse 
	- potassium and sodium move, facilitated diffusion from different gradients 
> gradients are built up by active transport 
> potassium-sodium pump (cotransport)
	- 3 Na ions 
	- ATP —> ADP + Pi
	- 3 Na ions out, 2 K ions in 
	- let Pi detaches

Question 26

How are things transported within a cell?

Answer 26

> from ER to Golgi apparatus
From Golgi apparatus to the membrane
in vesicles
- spheres of phospholipid bilateral

Question 27

How are vesicles formed?

Answer 27

• plasma membrane pulled (PM moves)
• pinched off

Question 28

What is endo- and exocytosis?

Answer 28

• endocytosis
  
  • forming a pit
  • engulfing the molecule
  • vesicles is formed and pinched off
    
    • inner layer outside
    • particles are digested (fusion with lysosome)
• exocytosis
  
  • vesicles with particle travel to PM
  • bilayers of membrane fuse
  • particles from vesicle are released

Question 29

How are cells formed?

Answer 29

• from division of existing cells

Question 30

Pasteur’s experiment

Answer 30

• swan-necked flasks
• hypothesis: pre-existing microorganisms in air can contaminate broth
• broth in flasks
  
  • boiled / unboiled
  • long / short necks
• the results showed that in boiled flasks with long necks there were no organisms

Question 31

How did first cells arise?

Answer 31

• production of carbon compounds
  
  • Miller-Urey experiment
    - carbon compounds arose from non-organic molecules
• assembly of carbon compounds
  
  • deep-sea vents
    
    • hot water + inorganic molecules
    • energy
  • assembling carbon compounds into polymers
• formation of membranes
  
  • phospholipids naturally form spherical membranes (vesicles)
    
    • amphipathic properties
• mechanism for inheritance
  
  • RNA was genetic material
    
    • self-replicating and catalyst

Question 32

What is the origin of eukaryotic cells?

Answer 32

> prokaryotic cell (doing anaerobic respiration) engulfed a different cell (aerobic)
- instead of digesting it, both cells lived in mutualism
- energy supply
during natural selection they were favoured

Question 33

What are the signs that mitochondria and chloroplasts were separate prokaryotes?

Answer 33

• their own DNA (circular)
• 70s ribosomes
• DNA transcription
  
  • mRNA used to synthesise proteins
• produced by division of pre-existing cells