Cell Biology

Question 1

explain the necessity of control experiments in general and give examples

Answer 1

The function of an experimental control is to hold the variables constant that the experiment isn’t interested in measuring. It helps scientists ensure that there have been no deviations in the environment of the experiment, besides the variable they are investigating. Example: James Lind of the Royal Navy solved the problem of the disease scurvy. He did so by putting sailors that had scurvy into the exact same room (conditions) and fed them the exact same diet, except on item. Some of the remedies included barely water, cider and a regiment of oranges and lemons. This created the first clinical trial, or test of the effectiveness of certain treatments in a controlled experiment.

Question 2

Characteristics of life

Answer 2

• Growth and development
• Cells
• Reproduction
• Excretion
• Movement
• Nutrition
• Respiration
• Irritability or sensitivity

Question 3

Light microscope

Answer 3

Microscopes: 	Light microscope;
Radiation source: 	Light; 
wavelength: 400-700 nm; 
lenses: Glass; 
specimen: Living or non-living; 
Max.resolution: 200 nm; 
Maximum useful magnification: 1000x / 1500 x;
Stains: Coloured dyes; 
Usage: Studying non subcellular organisms “normal”; 
Image: Coloured and 2D

Question 4

Transmission electron microscope

Answer 4

Transmission electron microscope (TEM);
Radiation source: Electron;
Wavelength: 0,005 nm; 
Lenses: Electromagnets;  
Specimen: Non – living (in a vacuum); 
Max. Resolution: 0,2-0,3 nm; 
Maximum useful magnification: 300 000 x;
Strains: Impregnated with heavy metals; 
Usage: Subcellular organisms;
Image: Monochrome (Black white), 2D

Question 5

Scanning electron microscope

Answer 5

Scanning electron microscope (SEM);
Radiation source: Electron; 
Wavelength: 0,005 nm; 
Lense: Electromagnets; 
Specimen: Non – living (in a vacuum);  
Max. resolution: 10 nm;  
Maximum useful magnification: 100 000 x; 
Stains: Coated in carbon or gold; 
Usage: Surface of the specimen; 
Image: Monochrome (Black & white), 3D

Question 6

Function of chloroplasts

Answer 6

Photosynthesis

Question 7

Function of Mitochondrion

Answer 7

Production of ATP through cellular respiration (through the energy from sugar, fats and other fuels with oxygen)

Question 8

Function of Nucleus

Answer 8

Nuclear lamina regulates exit and entry 
Chromosomes store DNA 
Nucleoli produce ribosome RNA 
-> Is used to build Ribosomes 
Synthesises messenger RNA according to what is provided by DNA. 
Duplication of DNA during mitosis

Question 9

Function of Dictyosomes

Answer 9

Modifying, storing, packaging proteins and lipids into vesicles
Receives and dispatches vesicles

Question 10

Function of Smooth endoplasmic Reticulum

Answer 10

Synthesis, metabolism and movement of liquids (Also steroids -> abundant in testes (ovaries)

Question 11

Function of Vacuole

Answer 11

Food storage -> minerals, sugar….

Contractile vacuoles regulate water volume

Question 12

Function of Cell Wall

Answer 12

Gives structure to the cell
Protects the cell
Prevents excessive uptake of water

Question 13

Function of Cytoskeleton

Answer 13

Gives mechanical support to cell (-> shape)
->Important for animal cells (back of walls)
Strong and resilience
Provides anchorage for many organelles and molecules
Quickly dismantled and reassembled in new location
Involved in cell mobility (movement for the interaction with proteins)
Muscular contraction
Cell division

Question 14

Function of Rough Endoplasmic reticulum

Answer 14

Synthesis of secretory proteins and their transport into membranes/organelles/out of cell

Question 15

Function of Ribosomes

Answer 15

Responsible for creating proteins by translating DNA

• Catalyses
• Secreted from cell

Question 16

Function of Lysosome

Answer 16

Digestion of macromolecules in cell
Dysome and food vacuole fuse
-> Enzyme then digest the food
-> Simple sugars, amino acids and other monomers
-> Pass into cytosol and become nutrients for the cell
Lysosome recycles cells and organises material -> anthophagy -> damage organelle is surrounded with membrane and fuses with dysosome

Question 17

Function of Peroxisome

Answer 17

2 Enzymes
Breaks down fatty acids into sugars (for mitochondria)
-> Transfer from Hydrogen to oxygen to oxygen substances -> H2O2 -> poisonous
Converts H2O2 to water -> detoxification

Question 18

Mitochondrion

Answer 18

Name of chemical reaction: Cell respiration

Chemical Formula: C6H12O6 + 6O2 –> 6CO2 + 6H2O + 36 or 38 ATP

Question 19

Chloroplast

Answer 19

Name of chemical reaction: Photosynthesis

Chemical Formula: 6CO2+6H2O→C6H12O6+6O2

Question 20

Structure Function principle

Answer 20

“With all biological structures the connection between the form and function can be seen (“form follows function”), e.g. the heart. The heart’s function is as a pump for blood. It needs to pump blood to the lungs for oxygenation and to the body to provide energy.
Its structure is that of a dual pump that pumps the oxygenated blood to the body and the deoxygenated blood to the lungs. Its muscle is made to contract so that it squeezes the blood out, and it has its own electrical system to ensure it keeps going if other systems fail.
nerve cells have long axons to conduct electrical impulses over long body distances (i.e. form backbone to big toe)

Question 21

Reaseach methods in cell biology to isolate cell organelles

Answer 21

1. Breaking cells and tissues.
   The first step on purification is to disrupt tissues and cells in a controlled fashion. Commonly used methods for homogenization:
   - Cells or tissues are broken open with high-frequency sound waves
   - A mild detergent is used to make holes in the plasma membrane
   - The cells are forced through a small hole using high pressure.
   - Shear cells are put between a close-fitting rotating plunger and a thick wall of a glass vessel.
   The resulting thick soup (called a homogenate or an extract) contains large and small molecules from the cytosol, such as enzymes, ribosomes and metabolites, as well as all the membrane-enclosed organelles. When carefully conducted, homogenization leaves most of the membrane-enclosed organelles intact.
2. Centrifugation
   - Differential Centrifugation or Cell Fractionation
   Is a technique used to extract cell organelles from cells so that they can be studied? The aim is to extract undamaged intact organelles. Samples must be kept very cool so that metabolism is slowed, and self-digestion of organelles is prevented. The samples must also be kept in a buffered, isotonic solution so that the organelles do not change volume and the enzymes are not desaturated by changes in pH. Centrifugation uses different speeds to separate cell components on the basis and density. The larger and denser components experience the greater centrifugal force and most move rapidly. They sediment to form a pellet at the bottom of the tube, while smaller, less dense components remain in suspension above, a portion called the supernatant (and the stuff at the bottom is called pellet).
3. Velocity Sedimentation or Density Gradient Centrifugation
   Here sucrose is added to the sample, which is then centrifuged at high speed. The organelle will form layers according to their specific buoyant densities (lower buoyant densities will settle at the top, whilst higher buoyant densities will settle at the bottom). There is an automated rack of small collecting tubes that allow the fractions to be collected.

Question 22

Cellular Differentiation

Answer 22

Cells that carry out a specialized function within a multicellular organism are differentiated, meaning that they are no longer able to divide and have a specific function to fulfil in the organism. The opposite is undifferentiated cells, which have no special structural properties and can still divide. E.g. In the plant cell the upper epidermis has he function of preventing uncontrolled water loss (transpiration) and mechanical damage. It is possible to identify the epidermis cells from their thick walls, which are covered with a transparent waterproof layer.

In the animal cell an example is the nerve cell, which have the task of transporting stimuli around the body, and therefore possess long extensions that transmit information.

Cells that are created for every single function are called totipotent cells. They can differentiate into all cell types but have fewer possibilities to develop further.

Question 23

Prokaryotic cells

Answer 23

• older
• The cells are found in Bacteria (or eubacteria) and archaea.
• No nucleus, genetic material loosely within the cell in the nucleoid region.
• DNA is circular and “naked”, called nucleoid and plasmid
• No compartments/ organelles (only ribosomes, cell wall, plasma membrane, cytoplasm, no mitochondria)
• Cell cycle goes between 20-26 mins

Question 24

Eukaryotic cells

Answer 24

• younger
• Cells are found in Animals, Plants, Protists and Fungi.
• Nucleus with a double membrane present
• DNA is linear and organized into histones
• Membrane-bond / membrane enclosed organelles; Structurally more complex
• Cell cycle goes between 12-24 hours

Question 25

Similarities of the Eukaryotic and PRokaryotic cell

Answer 25

• Both can exist in a multicellular organism

- Both have the same components, just minimally altered to serve the organism better.

Question 26

Endosymbiotic Theory:

Answer 26

The eukaryotic internal membrane server, called the endoplasmic reticulum, and the nuclear envelope may have evolved from infoldings of the plasma membrane in an ancestral prokaryotic cell. The theory of endosymbiosis proposes that a critical stage in the evolution of eukaryotic cells involved endosymbiotic relationships with prokaryotic organisms. Microorganisms that live within other cells are called endosymbionts. According to the theory, energy-producing bacteria may have been engulfed by a larger primitive cell and come to reside within it, eventually evolving into what we now know as mitochondria. Photosynthetic bacteria use photosynthetic pigments embedded in internal membranes to derive energy from sunlight. These bacteria may have come to live in early eukaryotic cells, leading to the evolution of chloroplasts.

Question 27

Proof of the endosymbiotic theory

Answer 27

• Mitochondria and chloroplasts contain their own circular DNA, like DNA in bacteria.
• Mitochondria are about the same size as bacteria
• Mitochondria appear to have been derived from purple bacteria, and chloroplasts devised from photosynthetic bacteria.
• Mitochondria and Plastids (Chloroplasts) have the same replication method.

Question 28

Development of the Biomembrane: 1917,1935,1935,1971,1971

Answer 28

• 1917; Langmuir: It was assumed that lipids float on the surface of water in a monolayer.
• 1935; Gorter and Grendel: It was concluded that the lipid layer was twice as big as the calculated surface of all erythrocyte membranes, the cell membrane was not a monolayer, but instead is a bilayer.
• 1935; Danielli and Davson: Lipids can isolate themselves from membranes and can attach themselves to proteins.
• 1972;Singer and Nicolson: It was discovered that the 2 layers of the lipid bilayer are not smooth, but instead structured. The breakage visible in the images is interpreted to occur along a protein molecule. This implies that the protein penetrates the membrane completely.
• 1972;Frye and Edidin: The proteins “float like icebergs in the sea” (fluid mosaic model), It was discovered that the membrane cannot be static, it is always in motion.

Question 29

Experiments used by the Biomembrane Reasearchers

Answer 29

• Freese fracture technique 1972: calls are frozen and then a knife is used to crack them open. The crack often passes through the interior of plasma and internal membranes. The “bumps” that appear are usually large proteins embedded in the interior of the membrane.
• Different coloured cells fused 1972 : Proteins were stained with different colour antibodies. The 2 differently stained cells were then fused. At first both colours were still clearly visible on the combined cell, then they became mixed. From this the fluid-mosaic model was discovered.
• Non-polar solvents to extract lipids from cell membranes 1935: Nonpolar solvents were used to extract lipids from the cell membranes of erythrocytes, and they were then put on the surface of water. The 2 scientists then proved that the lipid layer was twice as big as the calculated surface of all erythrocyte membranes. From this the cell membrane bilayer was discovered.
  The plasma membrane is a biomembrane that forms a barrier between the cytoplasm and the extracellular environment.
  The cell membrane according to the model of Singer and Nicolson, consists of a highly viscous fluid matrix of a bilayer of phospholipids having globular proteins associated with them. The phospholipid molecules in a cell membrane have their polar, hydrophilic heads towards the outer surface and the nonpolar, hydrophobic tails towards the inner surface. The arrangement forms a water-resistant barrier through which only lipid soluble substances can pass through.

Question 30

Global Proteins:

Answer 30

• Peripheral proteins: These are proteins that are partly projecting out of the lipid layer
• Integral proteins: These proteins are embedded in the phospholipid matrix and they penetrate the hydrophobic core of the lipid bilayer. They are also mainly called tunnel proteins, which are believed to have channels for the passage of water-soluble substances.

Question 31

Lipids in the biomembrane

Answer 31

Lipids ae a group of organic compounds with an oily, greasy or waxy consistency. They are relatively insoluble in water and tend to be water-repelling. They mostly consist of a glycerol molecule attached to 2 fatty acid chains and a Phospholipid group (PO43-). The Phospholipid group is the Hydrophilic end, and the Fatty acid chains are the hydrophobic end.

Question 32

Current biomembrane model

Answer 32

The currently accepted model for the structure of membranes is called the fluid-mosaic model. In this model, there is a double layer of phospholipids (bilayer) which are arranged with their hydrophobic tails facing inwards. The double layer of lipids is quite fluid with proteins floating in the layer, which have a number of functions.

Question 33

Structure of Cell Membranes

Answer 33

A cell membrane consists of two phospholipid layers. Each layer has an electrically charged and hydrophilic head, while the tail is uncharged and hydrophobic. The electrically charged heads of these layers face toward the water. The uncharged tails face each other. This makes it easier for small, neutrally charged molecules to pass through the cell membrane as opposed to charged and larger molecules. The phospholipid layers also prevent non-lipid soluble substances from passing through the cell membrane.

Question 34

Diffusion

Answer 34

The Random movement of molecules or other particles in liquid/air from an area of high concentration to an area of low concentration resulting in an even distribution of the particles based on the BROWNion motion. A solution on which the solute particles are uniformly distributed is said to be at equilibrium. If molecules are free to move, they move from high to low concentration until they are evenly dispersed (because of BROWNian motion).

Question 35

Osmosis:

Answer 35

The movement of water across a selectively permeable membrane (-> using specialized channels) from one region to another region where the water is more negative. The diffusion between two liquids (from a region of lower solute (=a substance that is dissolved) concentration to that of a higher solute (=dissolved substance) concentration) across a semipermeable membrane allows passage of the solvent (=a liquid that dissolves other substances; e.g.) (water), but no the solved solids.

Question 36

Plasmolysis

Answer 36

was the process of protoplasm (=is the living content of a cell that includes cytoplasm and the nucleus)shrinkage and detachment with the cell wall due to the loss of water when it placed in a solution with low water potential (hypertonic solution). Deplasmolysis is the reverse of plasmolysis. The key difference between the plasmolysis and deplasmolysis is that, during the plasmolysis, water molecules go out of the cell and cell protoplasm shrinks while during the deplasmolysis, water molecules enter the cell and cell protoplasm swells.

Question 37

Hypotonic:

Answer 37

A hypotonic solution is a solution that has a lower solute concentration compared to another solution.

Question 38

Isotonic

Answer 38

In chemistry, a solution is said to be isotonic when it has the same concentration of solutes as another solution across a semipermeable membrane.

Question 39

Hypertonic:

Answer 39

On the cellular and chemical levels, hypertonic fluids have a greater osmotic pressure than other fluids, and hypertonic solutions have a higher solution concentration than another, more diluted solution.

Question 40

Active transport

Answer 40

• Primary active transport
  Explanation: Involves the direct hydrolysis of ATP (-> cellular respiration in mitochondria) providing the energy required for the transport
  Examples. Uniport (transport substances one way): calcium – binding protein
  Antiport (molecules are transported at the same time, only both are transported in opposite directions (opposite is symport): sodium-potassium pump
• Secondary active transport
  Explanation: Energy is supplied by an ion concentration and electrical gradient established by active transport. Thus, ATP is used indirectly to set up the gradient. The ion moving down its electrochemical gradient is referred to as the driving ion because it is movement to this ion that drives the uphill movement of another ion/molecule (driven ion/molecule). In secondary active transport coupling between the driving and driven species is obligatory.
  Examples: Symport (2 Molecules are transported at the same time, in the same direction (opposite is antiport): sucrose H+ cotransport in plants (into vascular tissue); glucose and Na+ cotransport into epithermal cells of small intestine.

Question 41

Passive transport

Answer 41

Diffusion :
The Random movement of molecules or other particles in liquid/air from an area of high concentration to an area of low concentration resulting in an even distribution of the particles based on the BROWNion motion. A solution on which the solute particles are uniformly distributed is said to be at equilibrium. If molecules are free to move, they move from high to low concentration until they are evenly dispersed (because of BROWNian motion).
Osmosis:
Explanation: The movement of water across a selectively permeable membrane (-> using specialized channels) from one region to another region where the water is more negative. The diffusion between two liquids (from a region of lower solute (=a substance that is dissolved) concentration to that of a higher solute (=dissolved substance) concentration) across a semipermeable membrane allows passage of the solvent (=a liquid that dissolves other substances; e.g.) (water), but no the solved solids.

Question 42

Bulk transport

Answer 42

• Endocytosis ( “Normal Endocytosis”)
  A Part of the cell surface membrane is wrapped around the material which is supposed to enter the cell. A vesicle is formed which becomes detached from the plasma membrane.
• Endocytosis (Receptor-Mediated Endocytosis)
  Is used by animal cells to capture specific macromolecules from the cell’s environment. This process depends on receptor proteins, integral membrane proteins, that can bind to a specific molecule.
• Exocytosis
  Is the reverse process its endocytosis. Here a cell secretes macromolecules by the fusion of vesicles with the plasma membrane. Secretory vesicles carry their contents to the plasma membrane, then the vesicle fuses with the membrane and the contents are released. Exocytosis can be used by cells to dispose of waste material; however, often exocytosis is important in the secretion of useful substances.

Question 43

Factors that affect the rate of transport in cells

Answer 43

• The availability of a substrate
• The availability of carrier proteins.
• The availability of ATP

Question 44

Sodium potassium pump

Answer 44

Sodium-potassium pump minimises the concentration of Na+ moves down its concentration gradient using a symporter with glucose.
A Cytoplasmic Na+ binds to the sodium-potassium pump
B Extracellular K+ binds to the protein, triggering release of the phosphate group.
C K+ is released and NA+ sites are receptive again; the cycle repeats.
D Loss of the phosphate restores the proteins original confirmation.
E Na+ binding stimulates phosphorylation by ATP.
F Phosphorylation causes the protein to change its conformation, expelling NA+ to the outside.

Question 45

4 classes of organic molecules

Answer 45

• Lipids
  Include fats and oils for storing energy, phospholipids and glycolipids (structure of the cell membrane), waxes (protective surfaces for plants and animals) and steroids
• Carbohydrates
  Main energy-storage molecules in most organisms, used in making sugars.
  Proteins:
  Structural proteins like elastin and collagen provide support.
  Regulatory proteins control cell processes. Storage proteins produced in reproductive structures are a source of amino acids for developing organisms.
  Contractile proteins are responsible for movement of cells and organisms.
  Transport proteins carry substances from one place to another.
  Proteins also serve as antibodies, hormones, receptors and enzymes.
  Nucleic acids
  Make up the most important macromolecules; each is found in abundance in all living things, where they function in encoding, transmitting and expressing genetic information .

Question 46

What state are Membranes in

Answer 46

Membranes are fluid: lipids and some of the proteins can move laterally (happens often); sometimes they “flip-flop” across the membrane (rare). Unsaturated hydrocarbon tails of phospholipids have kinks that keep the molecules from packing together, enhancing membrane fluidity. Cholesterol (a sterile or modified steroid) reduces membrane fluidity, but at low temperatures it prevents tight packing of phospholipids, thus hindering solidification (temperature buffer) .

Question 47

What is the permability of a membrane affected by

Answer 47

The permeability of a cell membrane is affected by the polarity, electric charge and molar mass of the molecules that diffuse through it. The phospholipid layers that make up the cell membrane also affect its permeability.

Question 48

Function of select membrane permability

Answer 48

Cell membranes are selectively permeable, allowing some substances to pass through while restricting the passage of others. This is essential for providing a cell with nutrients, eliminating waste and preventing unwanted molecules from entering a cell. Cell membranes are very permeable to non-polar molecules, such as oxygen, nitrogen, carbon dioxide and steroids, membranes are less permeable to small polar molecules, such as water, glycerol, urea and ethanol, and highly impermeable to large polar molecules, such as glucose and sucrose. Electric charge also plays an important role in membrane permeability, charged particles, or ions, cannot penetrate a cell membrane. These charged particles, such as sodium, potassium, calcium, hydrogen and chlorine ions, require specialized transport proteins to carry them across the membrane

Question 49

large total surface area

Answer 49

One of the cell structures that has a large total surface area is the chloroplast. It namely has a larger membrane surface for enzymes and chlorophyll to do photosynthesis.