Cell theory 2

Question 1

Ribosome function

Answer 1

not organelles (no membrane) composed out of rRNA and proteins (formed in the nucleus) – made out of big and small subunit and there are 70S and 80S (Svedberg is the unit indicating how fast something sediments when centrifuged) – proteins synthesized on free ribosomes stay inside the cell and those synthesized on bound ribosomes get transported outside of the cell

Question 2

Plastid (example structure)

Answer 2

a family of double-membraned organelles like chloroplast (green) also exist red, orange, yellow… but only in plant cells – e.g. chloroplast surrounded by a double membrane, thylakoid membrane containing chlorophyll and other pigments, it is the site of photosynthesis (stroma, outer membrane, inner membrane, granum, thylakoids)

Question 3

Centrioles

Answer 3

elongated cylindrical structures present only in animal cells

Question 4

Mitochondria

Answer 4

the site of CR, surrounded by a double membrane (ribosomes, matrix, inner membrane, outer membrane, intermembrane space, starch grains, cristae, mDNA)

Question 5

Cilia and flagella

Answer 5

project from the cell surface, cilia are only present in animal cell and have the same function as pili in prokaryotic cells (attachment) while flagella is used for locomotion (movement)

Question 6

Do animals, fungi, and plants have these structures:
1) cell wall
2) vacuoles
3) plastids
4) centrioles
5) cilia
6) flagella

Answer 6

1) no, yes, yes
2) small, large, large
3) no, no, yes
4) yes, no, no
5) some, no, no
6) some, some, some

Question 7

What does the endosymbiotic theory say?

Answer 7

eukaryotes evolved from an anaerobic, one-celled common ancestor (with a nucleus) that reproduced either asexually by mitosis or sexually by meiosis and fertilization – mitochondria were formed by the endocytosis of aerobic heterotrophic bacteria by the common ancestor and chloroplasts by the endocytosis of photoautotrophic bacteria by the common ancestor

Question 8

What is the evidence for the endosymbiotic theory?

Answer 8

1| 70S ribosomes
2| Double membrane (vacuole)
3| Circular, naked DNA
4| Mitochondria divide by binary fission

Question 9

Cell differentiation

Answer 9

when cells develop along different pathways despite the same genome due to different gene expression because different chemical signals in the environment impact them

Question 10

How are tissues formed?

Answer 10

cells in the same environment (area) get influenced by the same chemicals and express the same genes (specialize for the same function) – cells of the same tissue interact and connect by cell-to-cell adhesion proteins (the integrity of the tissue is maintained) in all tissues except blood

Question 11

Housekeeping vs other genes

Answer 11

genes active in all cells that are required for basic life processes – other genes are expressed in only some cells because they cause the development of specialized structures, e.g. genes for the synthesis of hemoglobin only expressed during the development of erythrocytes

Question 12

Advantages of cell differentiation

Answer 12

1| Form can match function more specifically
2| A Specialist performs a function of life more efficiently than a generalist

Question 13

Advantages of multicellularity

Answer 13

1| Longer lifespan of the organism (death of one cell does not impact its survival
2| Larger body size possible (plants competing for light, predatory animals)
3| Effectiveness due to cell differentiation (more complex body forms can develop)

Question 14

Shared vs different features in viruses

Answer 14

shared:
1) non-cellular (no cytoplasm, metabolism or enzymes)
2) obligate intracellular parasites
3) no shared ancestor
4) small, fixed size (lack structural features, do not grow)
5) nucleic acid as genetic material (same genetic code as the host so that proteins can be synthesized)
6) capsids made of protein subunits
diverse features are in genes (no genes occur in all viruses) and structure (can be enveloped or non-enveloped)

Question 15

Viruses only have enzymes for:

Answer 15

1| Replication of genetic material
2| Infection of the host cells
3| Lysis (bursting host cells)

Question 16

Which genetic material can viruses have?

Answer 16

double/single-stranded DNA/RNA which can be circular/linear and can either be positive/negative sense (if it’s single-stranded)

Question 17

Positive vs negative sense strand

Answer 17

positive sense can be used immediately as mRNA while negative has to be transcribed before translation

Question 18

Viral membrane structure and function

Answer 18

made out of phospholipids (from the host) and glycoproteins (from the virus) – it helps the virus make contact and infect the host cell – only animal/human viruses are enveloped (plant and bacteriophages are mostly not)

Question 19

Spike proteins

Answer 19

receptors that initiate the fusion of the virus with the host cell

Question 20

Influenza, TMV (Tobacco Mosaic Virus), bacteriophage, COVID-19 and HIV (host cell, genetic info, membrane and extra info)

Answer 20

1) epithelial cells of the respiratory system, 8 SS negative-sense RNA, enveloped, RNA-replicase
2) plant cells, 1 SS positive-sense RNA, non-enveloped
3) bacteria, 1 DS DNA, non-enveloped
4) epithelial cells of the human respiratory system, SS positive-sense RNA, enveloped, spike proteins
5) human T-lymphocyte cells, 2 SS positive-sense RNA, enveloped, a retrovirus so converts RNA to DNA by reverse transcriptase (has the highest mutation rate)

Question 21

Lytic cycle steps

Answer 21

1| Attachment (to a host cell using tail fibers)
2| Penetration - genetic material entered via tail and pores in the membrane
3| DNA replication (100 copies)
4| Synthesis of viral proteins - using mRNA transcribed from viral genetic material
5| Assembly (of new viruses)
6| Lysis (host bursting)

Question 22

Lysogenic cycle

Answer 22

the viral genetic material becomes integrated into the host cell’s genetic material and becomes a prophage which gets inherited by next generations - virus is temperate in this state because it causes minimal harm to the host - stimulus for it changing to lytic state can come from inside or outside of the host

Question 23

Evidence for several origins of viruses

Answer 23

1| Obligate parasites (cells evolved before)
2| Use the same genetic code as living organisms (evolved from cells by losing cell components and life functions)
3| Diverse in structure and genetic constitution (similarities due to convergent evolution)
4| Evolved from cell components (some virus-like cell components)

Question 24

Main reasons for rapid rates of evolution in viruses

Answer 24

1| Short generation times (under an hour) in the lytic cycle
2| High mutation rates (RNA viruses)
3| Intense natural selection (host cells defending (antibodies))

Question 25

Why do influenza and HIV have high mutation rates?

Answer 25

in influenza RNA replicase replicates genetic material and does not proofread or correct errors (also transmission between species triggers evolution)
in HIV reverse transcriptase converts single-stranded RNA genome to DNA and does not proofread or correct errors – also the highest mutation rate produces genetically different strains, becomes resistant to drugs, evades the immune system, chronic infection

Question 26

Glycoproteins vs glycolipids

Answer 26

glycoproteins are polypeptides with carbohydrates attached and glycolipids are lipids (1-2 f.a.) with carbohydrates attached

Question 27

Role(s) of glycoproteins and glycolipids

Answer 27

1| Cell adhesion - form a carbohydrate-rich layer called glycocalyx (glycocalyx of adjacent cells can fuse)
2| Cell recognition - differences in the types of glycoproteins and glycolipids – e.g. immune system distinguishing between self and non-self-cells (destroying pathogens)

Question 28

What makes the membrane stable and what fluid?

Answer 28

stable: interactions between hydrophobic tails, hydrophilic heads, and hydrophobic tails and hydrophilic heads
fluid: lateral movement of protein and phospholipid molecules (up-down not possible)

Question 29

Role of saturated and unsaturated fatty acids in the membrane

Answer 29

saturated create a tightly packed structure of phospholipids because of their straight chains
unsaturated have bent chains so they make the membrane more permeable, fluid, and flexible, e.g. Antarctic fishes have more unsaturated fatty acids than tropic fishes

Question 30

Cholesterol

Answer 30

present in animal cells only, amphipathic – at low temp increases permeability and increases cell fluidity so that the cell doesn’t burst – at high temp maintains arrangement of the membrane, restricting movement, increasing viscosity, and decreasing permeability

Question 31

Types of globular proteins in the plasma membrane

Answer 31

integral (embedded, amphipathic) which can be transmembrane, and peripheral (attached, hydrophilic)

Question 32

Types of plasma membrane proteins (by function)

Answer 32

1| Channels for passive transport/pumps for active transport (aquaporin and Na/K pump)
2| Immobilized enzymes (NADP reductase)
3| Hormone receptor (insulin receptor)
4| Cell-to-cell recognition (antigens)
5| Cell-to-cell adhesion 6| Attachment site for cytoskeletons

Question 33

What property allows the cell to control the type and amount of substances that pass through the plasma membrane?

Answer 33

the specific diameter size and the chemical properties of channels

Question 34

Diffusion (and the two types)

Answer 34

the net movement of particles from a region of their higher to a region of their lower concentration (result of random movement of particles – orientation cannot be controlled)
simple is the diffusion of small, hydrophobic particles across a “bare” phospholipid layer (O2, CO2, ethanol, water)
facilitated is the diffusion of big, hydrophilic substances across the membrane through protein channels (glucose, proteins, sodium ions, water)

Question 35

Osmosis

Answer 35

the facilitated diffusion of water across a semi-permeable membrane from a region of lower solute concentration (hypotonic) to a region of higher solute concentration (hypertonic)

Question 36

Aquaporins function and where can they be found (which cells)

Answer 36

greatly increase membrane permeability to water molecules by transporting them, can be found in kidney cells and plant root cells

Question 37

How does active transport through protein pumps function?

Answer 37

the solute enters the pump and E from ATP changes the pump’s conformation so that its opening is on the other side of the membrane. The pump then goes back to its initial conformation spontaneously (no E/ATP required)

Question 38

Resting and active potential definition and value

Answer 38

resting: unequal distribution of charges on opposite sides of the membrane while the cell is at rest (-70 mV – slightly more Na+ on the outside than K+ inside the cell)
action potential: new distribution of charges across the membrane once the Na+ channels opened and let the ions inside (40 mV)

Question 39

When is the resting potential of the cell zero and why?

Answer 39

when the cell is dead because in that case there is no ATP to provide energy to the Na/K pump which, after Na+ and K+ diffuse down their concentration gradients through partially open channels, pumps them back to maintain the uneven charge distribution (called exchange transporter/antiporter)

Question 40

Nerve impulse

Answer 40

the change of polarity of the membrane: depolarization turns resting potential into action potential and repolarization is when K+ channels open and ions diffuse out of the cell, making the cell even less positive than it was before so the Na/K pump has to return the resting potential