AS Booklet 3- Viruses, Cell Structure, Cell Transport and Mitosis

Question 1

What are Viruses?

Answer 1

Viruses are non-living, acellular. Viruses have no nucleus, organelles, cell-surface membrane and no cytoplasm.

Question 2

What is the structure of a virus?

Answer 2

Capsid (usually protein), usually always genetic material either DNA or RNA. An envelope (mostly lipids) and attachment proteins.

Question 3

How do viruses replicate?

Answer 3

Non-living so they attach to specific host cell’s cell-surface membrane via attachment proteins.
Usually viruses inject genetic info into host cell. Viral DNA used as template to create viral proteins and eventually whole viruses which often release via lysis of the host cell.

Question 4

What is the cell structure of Prokaryotes?

Answer 4

Murein cell wall
Cell-surface membrane
Circular DNA molecule free in cytoplasm, not relation to a protein.
70s ribosomes.
Cytoplasm.
OCCASIONALLY: capsule surrounding cell wall, one+ plasmids, one+ flagella.

Question 5

What is the cell structure of Eukaryotes?

Answer 5

Cell-surface membrane.
Nucleus.
Linear DNA related to protein (histones).
Membrane-bound organelles.
80s ribosomes
Cytoplasm.

Question 6

What are the differences and similarities between the cell structures of prokaryotic cells and eukaryotic cells?

Answer 6

Differences: 70s vs 80s ribosomes. No organelles vs organelles No nucleus vs
Similarities: Cell-surface membrane.

Question 7

What are the named organelles of the eukaryotic cell?

Answer 7

Nucleus, Ribosome, Mitochondrium, SER and RER, Golgi body and apparatus, Lysosome, Chloroplast.

Question 8

What is the structure and function of the Nucleus of the eukaryotic cell?

Answer 8

Ribosomes, RER, pernicular space (in between inner and outer nuclear membrane, which forms nuclear envelope), nuclear pore, chromatin, nucleolus.

Contains DNA (genetic information) and more than one or more nucleoli.
Controls protein synthesis and therefore development and function of cell.

Question 9

What is the structure and function of the Ribosome of the eukaryotic cell?

Answer 9

Small, made up of protein and rRNA (small and large subunit) Appear in cytoplasm alone or on RER.
Used in protein synthesis, joins amino acids together.

Question 10

What is the structure and function of the SER and RER of the eukaryotic cell?

Answer 10

RER: has ribosomes on it that produce secretory enzymes. These secretory enzymes go to Golgi body for modification/packaging.
SER: doesn’t have ribosomes, involved in production and transport of lipids.

Question 11

What is the structure and function of the Golgi body and apparatus of the eukaryotic cell?

Answer 11

Golgi apparatus is flattened membrane sacs just like SER/RER.
Adds carbohydrates to proteins from RER, forming glycoproteins.
Packages proteins/glycoproteins into Golgi vesicles for secretion.
Produces lysosomes that contain lysozymes (hydrologic enzymes).

Question 12

What is the structure and function of the Mitochondria of the eukaryotic cell?

Answer 12

Circular DNA. 
Matrix.
Inter membrane space.
Enzymes.
Inner membrane.
Outer membrane.
Cristal.
80s ribosomes. 
Function is the place where respiration takes place.

Question 13

What is the structure and function of the Lysosomes of the eukaryotic cell?

Answer 13

Membrane sacs containing hydrolytic enzymes. Enzymes are kept separately so as not to destroy the cell.
Formed by Golgi Apparatus.

Functions:
Digestion of material from phagocytosis. Fuse with vesicles and release hydrolytic enzymes to digest the material and then this is deposited outside of the cell (lysosome fuses with membrane to release it).
Organelles that don’t work anymore/are non-functional are engulfed digested.
Release of hydrolytic enzymes outside of cell.

Question 14

What is the structure and function of the Chloroplast in eukaryotic plant cells?

Answer 14

Lipid droplets.
Circular DNA.
Outer membrane.
Inner membrane.
Stroma.
Granum.
Thylakoid.
Membrane-bound AND free 80s ribosomes.
Starch grains.

Question 15

What is the structure of a eukaryotic plant cell?

Answer 15

Murein Cell wall.
Cell-surface membrane.
RER and SER.
Golgi Apparatus.
Nucleolus.
Nucleus.
Chromatin.
Large vacuole.
Cytosol.
Mitochondria.
Plasmodesmata- fine strands that connect to adjacent cells.

Question 16

Give a description of one type of cell from a multicellular organism?

Answer 16

An epithelial cell from the lining of the ileum.
Microvili, RER, SER, Golgi Apparatus, Cytoplasm, Nucleus, Nuclear membrane, 80s Ribosomes, cell-surface membrane, mitochondria.

Question 17

What are the definitions of tissues, organs and systems?

Answer 17

Tissues: groups of similar cells performing specific functions, with a common origin.
Organs: different tissues, which have specific functions.
Systems: consists of two or more organs working together.

Question 18

What is the process of cell fractionation and ultracentrifugation?

Answer 18

• Cells homogenised (by grinding) to release stuff within cell membrane and put into ice cold isotonic buffer solution, prevents damage to organelles by osmosis, pH or temperature change, enzymes hydrolysing them due to increase in temp = increase in KE.
• Suspension is put into centrifuge at low speed.
• Sediment and supernatant are divided.
• Supernatant mixed at medium speed.
• New sediment and supernatant separated.
• Supernatant mixed at high speed.
• Sediment and supernatant separated, supernatant is soluble protein.

Have to spin at low speed-high speed because at high speed immediately, all organelles would sink.

Question 19

What is Electron Microscopy?

Answer 19

The use of a beam of electrons to magnify a sample.

Question 20

What are the advantages and disadvantages of Electron Microscopy?

Answer 20

Advantages:
• There is a greater resolution because electrons have shorter wavelengths of light.
Disadvantages:
• Vacuum is required so live samples can’t be seen.
• Preparation involving staining is more complicated than light microscopy + can result in artefacts.
• Thin sections must be prepared.
Images aren’t in colour.

Question 21

How does a transmission electron microscope (TEM) work?

Answer 21

• Uses a beam of electrons focused by electromagnets.
• Specimen must be thing, stained by electron-dense substances like heavy metal salts.
• These substances deflect electrons and pattern made by remaining electrons of the beam passing through specimen converted to image.

Question 22

How does a scanning electron microscope (SEM) work?

Answer 22

• Specimen coated with thin film of heavy metal like gold.
• Electron beam is scanned to and fro across specimen.
• Electrons reflected from surface produce image seen.

Question 23

What are the advantages and disadvantages of a TEM?

Answer 23

Advantages:
• Higher resolution than SEM.
• Can see internal structures (proteins, nucleic acids etc).
Disadvantages:
• Isn't 3D.
• No colour.

Question 24

What are the advantages and disadvantages of an SEM?

Answer 24

Advantages:
• Surfaces of structure shown.
• 3D effect.
• Thicker sections can be examined than in TEM.
Disadvantages:
• Lower resolution than TEM.
• Only surface (of cross-section) can be viewed.

Question 25

How do you calculate the size of cellular structures (microscope formula)?

Answer 25

IMA
Image = magnification x actual.
Actual size = real life size.
Image size = magnified size.

Question 26

How do you convert units?

Answer 26

mm-µm-nm

x 1000 each time or divide 1000.

Question 27

What is the structure of the cell-surface membrane?

Answer 27

Phospholipid bilayer:
• Phospholipids in two layers, hydrophobic fatty acid tails facing outwards and hydrophilic phosphate heads facing onwards towards each other.
• Cholesterol embedded in membrane.
• Proteins embedded in membrane.
• Carbohydrate chains, often forming glycolipids and glycoproteins due to being attached to lipids or proteins, respectively.
• Unsaturated and saturated fatty acids.

Question 28

Which molecules can get through the cell surface membrane and how?

Answer 28

Small, large, charged.
• Small molecules such as CO2 and O2 can diffuse between the gaps between molecules of the phospholipid bilayers. H2O can pass through aquaporins by osmosis.
• Carrier Proteins allow specific/certain molecules through by facilitated diffusion and active transport.
• Channel Proteins allow specific/certain molecules through by facilitated diffusion.
• Water soluble ions and polar ions cannot pass through cell membrane.
• Lipid soluble molecules can pass through the cell surface membrane, bad because harmful molecules such as benzene can get into cell.

Question 29

What are the different types of transport across cell membranes and how do they differ?

Answer 29

Diffusion, active transport and facilitated diffusion.
• Diffusion is passive (does not require energy from respiration).
• Facilitated diffusion is passive.
• Active transport is active, so requires energy from the hydrolysis of ATP.

Question 30

What is diffusion?

Answer 30

The net movement of molecules from a high concentration to a low concentration.
Doesn’t use energy.

Question 31

What is facilitated diffusion?

Answer 31

Allows the transport of polar molecules such as glucose and amino acids across membranes down a concentration gradient.

In Carrier Proteins, molecule fuses with protein to cause a change in the tertiary structure which allows the protein to pass through.

In Channel Proteins, there is no shape change.

Question 32

What is active transport?

Answer 32

Movement of molecules or ions through partially permeable membranes.
Phosphate group from energy in ATP attaches to carrier protein and activates protein to accept the particle to be transported.
Energy of the phosphate group attaching to the protein is used to change the shape, transporting the molecule.

Question 33

What is osmosis?

Answer 33

The net movement of water molecules from a high concentration to a low concentration.

Question 34

What is Water Potential and how does it effect cells?

Answer 34

The potential of water molecules to leave a solution by osmosis.
Higher water potential —> lower water potential.
Pure water = 0
Less negative = more water.
More negative = less water.

If a cell is in a solution with a higher water potential, the cell will lose water via osmosis and plant cells become plasmolysed (cell membrane comes away from cell wall).
If a cell is in a solution with a lower water potential, the cell will gain water via osmosis and this can result in the cell bursting (osmolysis).

Question 35

What is DNA?

What are chromosomes?

Answer 35

Deoxyribose nucleic acid is genetic material wrapped around histones (protein).
Chromosomes are thread-like structures that DNA is organised into during cell division (in eukaryotes).

Question 36

What is mitosis? What are the 5 stages of mitosis called?

Answer 36

Mitosis is the process by which two new (daughter) cells are created from a single (parent) cell.
The stages of mitosis are interphase, prophase, anaphase, metaphase, telophase followed by cytokinesis.

Question 37

Describe each stage of mitosis.

Answer 37

Interphase:

• DNA content is doubled, as are organelles.
• Increase in protein synthesis.

Prophase:

• Chromosomes joined by centromeres. They shorten and thicken.
• Centrioles move to opposite poles (not present in plant cells).
• Nuclear membrane breaks down.

Metaphase:

• Centrioles form spindles (consists of protein microtubules).
• Chromosomes move to equator of spindle and attaches via centriole.
• Sister chromatid orientated towards opposite poles of the cell, horizontal.

Anaphase:
- Centromere splits, sister chromatids separated and pulled to opposite poles of the cell by the spindles.

Telophase:

• Chromatids at opposite ends of cell begin to uncoil.
• Nuclear membrane reforms.

Cytokenesis:
- The splitting of the cytoplasm into two, with the cell membrane

Question 38

How is cancer linked to cell division?

Answer 38

Uncontrolled growth can lead to cancer. Uncontrolled growth occurs when the cell cycle is not regulated due to mutations in the genes (proto-oncogenes and tumour-suppressor genes). This could result in a cell being in the interphase section of the cycle much, much shorter than usual so that they can rapidly divide, forming a tumour.

Question 39

How do Prokaryotes reproduce?

Answer 39

Binary Fission.
The circular DNA and plasmid DNA is replicated. The cell elongates as this happens. The cell wall and plasma membrane divide and the cells separate. Identical daughter cells.

Question 40

How do you calculate the population in a certain generation of bacteria?

Answer 40

Population in the nth generation = 2 to the power of n (2^n).
n = number of generations so after 4 generations the population would be:
2^4 = 2 x 2 x 2 x 2 = 16 cells.

Question 41

What components of a cell separate at which bit of centrifugation?

Answer 41

Nuclei.
Mitochondria and chloroplasts.
ER, ribosomes.

Question 42

What is the definition of resolution?

What is the definition of artefacts?

Answer 42

Resolution: ability to distinguish between two close objects.
Artefacts: False images arising from poor technique.

Question 43

What does each bit of the phospholipid bilayer do?

Answer 43

• Molecules of phospholipid move creating fluid structure.
• Proteins in membrane are unevenly distributed, creating mosaic.
• Partial permeability due to proteins and phospholipids in membranes.
• Proteins act as carrier or channel proteins.
• Some proteins act as specific receptors to hormones.
• Glycolipids and glycoproteins act as both receptors and also as antigens in cell-cell recognition.
• Cholesterol restricts movement of phospholipids so membrane is less fluid and less ions are lost.

Question 44

What is the rate of diffusion proportional to?

Answer 44

Rate of diffusion is PROPORTIONAL TO
surface x concentration difference
————————————————
Thickness of exchange surface

Concentration difference = gradient.