1 The cell

Question 1

What are the three original tenets of cell theory and what is newer fourth?

Answer 1

• All living things are composed of cells
• The cell is the basic functional unit of life
• Cells arise only from preexisting cells

New: Cells carry genetic material in the form of deoxyribonucleic acid (DNA). This genetic material is passed on from parent to daughter cell.

Question 2

Why are viruses not considered living organisms?

Answer 2

They violate two of the tenets of cell theory:

Unable to reproduce on their own (don’t arise from preexisting cells and have ribonucleic acid (RNA) sometimes instead of DNA

Question 3

Where is ribosomal RNA (rRNA) synthesized?

Answer 3

The nucleolus

Question 4

What is the paradigmatic example of cytoplasmic or extranuclear inheritance (the transmission of genetic material independent of the nucleus)?

Answer 4

The mitochondria, which replicate independently of the nucleus via binary fission.

Mitochondria are thought to have evolved from an anearobic prokaryote engulfing an aerobic prokaryote (early mitochondria) and establishing a symbiotic relationship.

Question 5

What organelle is responsible for kicking off apoptosis?

Answer 5

The mitochondria, by releasing enzymes involved in the electron transport chain.

Question 6

What are lysosomes?

Answer 6

Lysosome pathway is for degradation

• membrane bound structures containing hydrolytic enzymes
• Break down things ingested and cellular waste products
• Function with endosomes, which transport, package, and sort cell material to and from the membrane, golgi apparatus, or lysosomal degradation pathway
• Release of enzyme content is called autolysis and can kick off apoptosis as well as mitochondria (these enzymes directly degrade cellular machinery however).

Question 7

What are the smooth and rough endoplasmic reticulums?

Answer 7

Rough: contain ribosomes which synthesize proteins

Smooth: lipid synthesis (e.g. for cell membrane), detoxifying, shuttling proteins from the rough endoplasmic reticulum to the golgi apparatus for shipping out.

Question 8

What is the golgi apparatus?

Answer 8

Stacked membrane bound sacs. Proteins are sent here from endoplasmic reticulum. They are modified here (e.g. signal added, carb/protein/lipids added etc.). And sent to other parts of the cell or to the cell membrane in secretory vesicles for exocytosis.

Question 9

What are peroxisomes?

Answer 9

Organelles that contain hydrogen peroxide. Breakdown of very long fatty acids via beta-oxidation.

Participating in the synthesis of phospholipids and contain some of the enzymes involved in the pentose phosphate pathway.

Question 10

What are the three components of the cytoskeleton?

Answer 10

• Microfilaments: actin, provide structural integrity, can generate movement with myosin, form the cleavage furrow in mitosis. Can withstand compression/fracture.
• Microtubules: Tubulin (hollow polymers, 9 microtubules form ring, two in the centre), primary pathways for motor proteins kinesin and dynein carry vesicles. Compose cilia and flagella.Centrioles found in centrosomes. Microtubues emanating from centrioles attach to the chromosomes via kinetochores and can pull sister chromatids apart.
• Intermediate filaments: filamentous proteins (diverse), cell-cell adhesion, maintenance of cytoskeleton integrity, can withstand pulling tension. Anchor organelles (including nucleus).

Question 11

What are microfilaments?

Answer 11

• Microfilaments: actin, provide structural integrity, can generate movement with myosin, form the cleavage furrow in mitosis. Can withstand compression/fracture.

Question 12

What are microtubules?

Answer 12

• Microtubules: Tubulin (hollow polymers, 9 microtubules form ring, two in the centre), primary pathways for motor proteins kinesin and dynein carry vesicles. Compose cilia and flagella.Centrioles found in centrosomes. Microtubues emanating from centrioles attach to the chromosomes via kinetochores and can pull sister chromatids apart.

Question 13

What are intermediate filaments?

Answer 13

• Intermediate filaments: filamentous proteins (diverse), cell-cell adhesion, maintenance of cytoskeleton integrity, can withstand pulling tension. Anchor organelles (including nucleus).

Question 14

What type of cells form the parenchyma (functional tissue parts of an organ)?

Answer 14

Epithelial tissue cells which are often polarized (facing a lumen)

Epithelia classified based on layers:

• Simple epithelia (one layer)
• Stratified epithelia (multiple layers)
• Pseudostratified epithelia (appear to have multiple layers due to varying cell height, but in reality, one layer).

Question 15

Connective tissues are the main contributors to the_____ or support structure. Most cells in connective tissues produce and secrete materials such as _____ and _____ to form the ____________.

Answer 15

Connective tissues are the main contributors to the stroma or support structure. Most cells in connective tissues produce and secrete materials such as elastin and collagen to form the extracellular matrix.

Question 16

Many archaea are chemosynethetic. How does this make them unique?

Answer 16

Able to generate energy from inorganic compounds, including sulfur and nitrogen based compounds such as ammonia which helps them act as extremophiles in some cases.

Question 17

What are aerotolerant anaerobes?

Answer 17

Bacteria that are unable to use oxygen for metabolism, but are not harmed by its presence in the environment.

Question 18

Describe the envelope of a bacterium and gram staining.

Answer 18

The envelope of a bacterium is comprised of two parts, outer wall and cell membrane.

The outer is a cell wall, which protecs and controls movement of solutes into and out of the bacterium. The cell wall can be gram positive or gram negative (depending on crystal violet stain followed by counterstain with safranin). The stain will take if a thick layer of peptidoglycan, which can protect from the immune system (adaptive). There is also lipoteichoic acid, which can trigger the human immune system (maladaptive).

Gram negative cell walls are very thin and contain a much smaller amount of peptidoglycan. They also have an outer membrane with lipopolysaccharides, which triggers a much more pronounced inflammatory response than to lipoteichoic acid.

Question 19

True or false? Archaea are more close to eukaryotes than prokaryotes?

Answer 19

True! Archaea have more similarities to eukaryotes, including having true histones

Question 20

Where does the generation of ATP happen in prokaryotes?

Answer 20

The electron transport chain occurs on the cell membrane in prokaryotes.

Question 21

What are the two ribosomal subunits for eukaryotes and prokaryotes respectively? Which is bigger?

Answer 21

Eukaryotes: 40S and 60S

Prokaryotes: 30S and 50S

Eukaryotes are bigger

Question 22

Give three unique features of plasmids

Answer 22

• Contained outside bacterium genome
• May carry virulence factors that increase how pathogenic a bacterium is (e.g. toxin production)
• Episomes are plasmids that are capable of integrating into the genome of the bacterium

Question 23

Bacterial genetic recombination helps increase bacterial diversity and thus permits evolution of a bacterial species over time. These recombination processes include ________, _______, and ________.

Answer 23

Transformation: integration of foreign genetic material into the host genome (e.g. from lysed bacteriums)

Conjugation: Conjugation bridge (sex pili) facilitates transfer of genetic material from donor male (+) to recipient female (-).

Transduction: Requires a vector (a virus that carries genetic material from one bacterium to another). Bacteriophages can accidentally trap a segment of host DNA during assembly. When the bacteriophasge infects another bacterium it can release this trapped DNA into the new host cell and therefore transfer DNA giving the host new genes.

Question 24

What are the four phases of the bacterial growth curve? What are the features of each phase?

Answer 24

1. Lag phase: adapting to environment
2. Exponential phase: exponential growth
3. Stationary phase: resources reach equilibrium (depletion:production)
4. Death phase: resources are used up

Question 25

How does the presence of an envelope help or hinder viruses?

Answer 25

If an envelope is present, it will surround the capsid and is composed of phospholipids and virus-specific proteins. The envelope is very sensitive to heat, detergents, and desiccation; thus enveloped viruses are easier to kill.

Viruses without an envelope are more resistant to sterilization.

Question 26

What is the difference between positive sense RNA viruses and negative sense RNA viruses?

Answer 26

Positive sense: genome may be directly translated to functional proteins by the ribosomes of the host cell

Negative sense: synthesis of an RNA strand complementary to the negative-sense RNA strand, which can then be used as a template for protein synthesis. Negative sense RNA viruses must carry an RNA replicase in the virion to ensure that the complimentary strand is synthesized.

Question 27

What enzymes MUST retroviruses carry?

Answer 27

reverse transcriptase, which synthesizes DNA from single-stranded RNA. the DNA then integrates into the host cell genome, where it is replicated and transcribed as if it were the host cell’s own DNA.

This makes the virus exceptionally hard to kill (to completely kill you have to kill infected cells as well). And is one of the reasons HIV is so hard to treat.

Question 28

What does it mean for a virus to be in a ‘productive cycle?’

Answer 28

A virus can leave the cell by fusing with its plasma membrane (extrusion). This keeps the host cell alive and able to make more copies (rather than the buildup of virions and subsequent lysing of the host cell that occurs with some viruses).

Question 29

Compare and contrast the lytic and lysogenic cycles of bacteriophages

Answer 29

One key difference between the lytic cycle and the lysogenic cycle is that the lysogenic cycle does not lyse the host cell straight away. Phages that replicate only via the lytic cycle are known as virulent phages while phages that replicate using both lytic and lysogenic cycles are known as temperate phages.

Question 30

What are prions and viroids?

Answer 30

Prions: Infectious proteins that cause disease by triggering misfolding of other proteins (usually from alpha helices to beta pleated sheets). Protein aggregates form and cell function is reduced. Familial fatal insomnia, mad cow disease etc.

Viroids: Small pathogens consisting of very short circular single-stranded RNA that infect plants. Silence genes in plant genome by binding to RNA sequences. Can cause metabolic and structural derangements in the plant cell. Hepatitis D virus is a human example of viroids, but unable to exert silencing effect on human hepatocytes without HBV.