Chapter 1 The Cell

Question 1

The cell theory

Answer 1

• All living things are composed of cells.
• The cell is the basic functional unit of life.
• Cells arise only from preexisting cells.
• Cells carry genetic information in the form of DNA. This genetic material is passed on from parent to daughter cell.

Question 2

Viruses are not considered living things because they are

Answer 2

acellular

cannot reproduce without the assistance of a host cell

may use RNA as their genetic material.

Question 3

Eukaryotes have what?

Answer 3

Eukaryotes have membrane-bound organelles

a nucleus

form multi-cellular organisms.

Question 4

The cell membrane and membranes of organelles contain

Answer 4

The cell membrane and membranes of organelles contain phospholipids, which organize to form hydrophilic exterior and hydrophobic interior.

Question 5

The cytosol suspends the

Answer 5

The cytosol suspends the organelles and allows diffusion of molecules through-out the cell.

Question 6

The eukaryotic organelles each serve specific functions:

Answer 6

Nucleus. Nucleoli. Mitochondria ( outer membrane, and inner membrane). Lysosomes. endoplasmic reticulum (ER) both the smooth and rough ER. Golgi apparatus. Peroxisomes.

• The nucleus contains DNA organized into chromosomes. It is surrounded by the nuclear membrane or envelope, a double membrane that contains nuclear pores for two-way exchange of materials between the nucleus and cytosol. DNA is organized into coding regions called genes.
• The nucleolus is a subsection of the nucleus in which ribosomal RNA (rRNA) is synthesized.
• Mitochondria contain an outer and inner membrane. The outer membrane forms a barrier with the cytosol; the inner membrane is folded into cristae and contains enzymes for the electron transport chain. Between the mem-branes is the intermembrane space; inside the inner mitochondrial mem-brane is the mitochondrial matrix. Mitochondria can divide independently of the nucleus via binary fission and can trigger apoptosis by releasing mitochondrial enzymes into the cytoplasm.
• Lysosomes contain hydrolytic enzymes that can break down substances ingested by endocytosis and cellular waste products. When these enzymes are released, autolysis of the cell can occur.
• The endoplasmic reticulum (ER): interconnected membranes and is continuous with the nuclear envelope. The rough ER (RER) is studded with ribosomes, which permit translation of proteins destined for secretion. The smooth ER (SER) is used for lipid synthesis and detoxification.
• The Golgi apparatus consists of stacked membrane-bound sacs in which cellular products can be modified, packaged, and directed to specific cellular locations.
• Peroxisomes contain hydrogen peroxide and can break down very long chain fatty acids via β-oxidation. They also participate in phospholipid synthesis and the pentose phosphate pathway.

Question 7

The cytoskeleton provides

Answer 7

provides stability and rigidity to the overall structure of the cell

providing transport pathways for molecules within the cell.

Question 8

Microfilaments

Answer 8

Microfilaments composed of actin.

They provide structural protection for the cell and can cause muscle contraction through interactions with myosin.

They also help form the cleavage furrow during cytokinesis in mitosis.

Question 9

Microtubules

Answer 9

Microtubules composed of tubulin.

Create pathways for motor proteins like kinesin and dynein to carry vesicles.

also contribute to the structure of cilia and flagella, where they are organized into nine pairs of microtubules in a ring with two microtubules at the center (9 + 2 structure).

Centrioles are found in centrosomes and are involved in microtubule orga-nization in the mitotic spindle.

Question 10

Intermediate filaments

Answer 10

Intermediate filaments are involved in cell–cell adhesion and maintenance of the integrity of the cytoskeleton; they help anchor organelles. Common examples include keratin and desmin.

Question 11

Epithelial tissues cover the

Answer 11

Epithelial tissues cover the body and line its cavities, protecting against patho-gen invasion and desiccation. Some epithelial cells absorb or secrete substances, or participate in sensation.

Question 12

In most organs, epithelial cells form the

Answer 12

In most organs, epithelial cells form the parenchyma, or the functional parts of the organ.

Question 13

Epithelial cells may be

Answer 13

Epithelial cells may be polarized, with one side facing a lumen or the outside world, and the other side facing blood vessels and structural cells.

Question 14

Epithelia can be classified by

Answer 14

Epithelia can be classified by the number of layers:

simple epithelia have one layer

stratified epithelia have many layers

pseudostratified epithelia appear to have multiple layers due to differences in cell heights, but actually have only one layer.

Question 15

Epithelia can be classified by the

Answer 15

Epithelia can be classified by the shapes of the cells:

cuboidal cells are cube-shaped

columnar cells are long and narrow

squamous cells are flat and scale-like

Question 16

Connective tissues does what? In most organs, connective tissues form the?
Ex of connective tissues?

Answer 16

Connective tissues support the body and provide a framework for epithelial cells.

Whereas epithelial cells contribute to the parenchyma of an organ, connective tissue are the main contributors to the stroma or support structure. In most organs, connective tissues form the stroma or support structure by secreting materials to form an extracellular matrix.

Bone

cartilage

tendons

ligaments

adipose tissue

blood are all connective tissues.

Question 17

Prokaryotes do not contain

Answer 17

membrane-bound organelles; they contain their genetic material in a single circular molecule of DNA located in the nucleoid region.

Question 18

There are three overarching domains of life and how many account for prokaryotic or eukaryotic?

Answer 18

prokaryotes account for two of these:

• Archaea are often extremophiles, living in harsh environments (high temperature, high salinity, no light) and often use chemical sources of energy (chemosynthesis) rather than light (photosynthesis). They have similarities to both eukaryotes (start translation with methionine, similar RNA poly-merases, histones) and bacteria (single circular chromosome, divide by binary fission or budding).
• Bacteria have many similar structures to eukaryotes, and have complex relationships with humans, including mutualistic symbiosis and pathogenesis.
• Eukarya is the only non-prokaryotic domain.

Question 19

Bacteria can be classified by shape:

Answer 19

1. Cocci
2. Bacilli
3. Spirilli

• Spherical bacteria are called cocci.
• Rod-shaped bacteria are called bacilli.
• Spiral-shaped bacteria are called spirilli.

Question 20

Spherical bacteria are called

Answer 20

cocci

Question 21

Rod-shaped bacteria are called

Answer 21

bacilli

Question 22

Spiral-shaped bacteria are called

Answer 22

spirilli

Question 23

Bacteria can be classified based on metabolic processes:

Answer 23

• Obligate aerobes ——require oxygen for metabolism.
• Obligate anaerobes ——cannot survive in oxygen-containing environments and can only carry out anaerobic metabolism.
• Facultative anaerobes ——can survive in environments with or without oxygen and will toggle between metabolic processes based on the environment.
• Aerotolerant anaerobes ——cannot use oxygen for metabolism, but can survive in an oxygen-containing environment.

Question 24

The cell wall and cell membrane of bacteria form the

Answer 24

The cell wall and cell membrane of bacteria form the envelope.

Together, they control the movement of solutes into and out of the cell.

Question 25

Bacteria can be classified by

Answer 25

Bacteria can be classified by the color their cell walls turn during Gram staining with a crystal violet stain, followed by a counterstain with safranin. Gram-positive bacteria turn purple, while gram-negative bacteria turn pink-red.

• Gram-positive bacteria have a thick cell wall composed of peptidoglycan(apolymeric substance made from aa and sugars) and lipoteichoic acid.
• Gram-negative bacteria have a thin cell wall composed of peptidoglycan and an outer membrane containing phospholipids and lipopolysaccharides (triggers an immune response in human beings; the inflammatory response to lipopolysaccharides is much stronger than the response to lipoteichoic acid).

Question 26

Bacteria may have one, two, or many?

Answer 26

Bacteria may have one, two, or many flagella that generate propulsion to move the bacterium toward food or away from immune cells. Moving in response to chemical stimuli is called chemotaxis. Bacterial flagella contain a filament composed of flagellin, a basal body that anchors and rotates the flagellum, and a hook that connects the two.

Prokaryotes carry out the electron transport chain using the cell membrane.

• Prokaryotic ribosomes are smaller than eukaryotic ribosomes (30S and 50S, rather than 40S and 60S).

Question 27

Prokaryotes multiply through ___, in which the

Answer 27

Prokaryotes multiply through binary fission,

in which the chromosome replicates while the cell grows in size, until the cell wall begins to grow inward along the midline of the cell and divides it into two identical daughter cells.

Question 28

In addition to the single circular chromosome in prokaryotes

plasmids that integrate in genome are called what?

Answer 28

extrachromosomal material can be carried in plasmids. Plasmids may contain antibiotic resistance genes or virulence factors.

Plasmids that can integrate into the genome are called episomes.

Question 29

Bacterial genetic recombination increases bacterial diversity.

Answer 29

1 Transformation
2 Conjugation
3 Transduction
4 Transposons

• Transformation occurs when genetic material from the surroundings is taken up by a cell, which can incorporate this material into its genome.
• Conjugation is the transfer of genetic material from one bacterium to another across a conjugation bridge; a plasmid can be transferred from F+ cells to F− cells, or a portion of the genome can be transferred from an Hfr cell to a recipient.
• Transduction is the transfer of genetic material from one bacterium to another via a bacteriophage vector.
• Transposons are genetic elements that can insert into or remove themselves from the genome.

Question 30

Transformation

Answer 30

Transformation occurs when genetic material from the surroundings is taken up by a cell, which can incorporate this material into its genome.

Foreign genetic material comes from other bacteria that, upon lysing, spill their contents into the vicinity of a bacterium cable of transformation. Many gram negative rods are able to carry out this process.

Question 31

Conjugation

Answer 31

Conjugation is the transfer of genetic material from one bacterium to another across a conjugation bridge; a plasmid can be transferred from F+ cells to F− cells, or a portion of the genome can be transferred from an Hfr cell to a recipient.

Detailed explanation:

Conjugation is the bacterial form of mating (sexual reproduction). It involves two cells forming a conjugation bridge between them that facilitates the transfer of genetic material. The transfer is unidirectional, from the donor male (+) to the recipient female (−). The bridge is made from appendages called sex pili that are found on the donor male. To form the pilus, bacteria must contain plasmids known as sex factors that contain the necessary genes. The best-studied sex factor is the F (fertility) factor in E. coli. Bacteria possessing this plasmid are termed F+ cells; those without are called F− cells. During conjugation the F+ cell replicates its F factor and donates the copy to the F− cell, converting it to an F+ cell. This enables the cell obtaining the new plasmid to then transfer copies to other cells. This method of genetic recombination allows for rapid acquisition of antibiotic resistance or virulence factors throughout a colony because other plasmids can also be passed through the conjugation bridge.

The sex factor is a plasmid, but through processes such as transformation, it can become integrated into the host genome. In this case, when conjugation occurs, the entire genome replicates because it now contains the sex factor. The donor cell will then attempt to transfer an entire copy of its genome into the recipient; however, the bridge usually breaks before the full DNA sequence can be moved. Cells that have undergone this change are referred to by the abbreviation Hfr for high frequency of recombination.

Question 32

Transduction

Answer 32

Transduction is the transfer of genetic material from one bacterium to another via a bacteriophage vector.

Question 33

Transposons

Answer 33

Transposons are genetic elements that can insert into or remove themselves from the genome.

Question 34

bacteriophages

Answer 34

viruses that infect bacteria

Question 35

Bacterial growth follows a predictable pattern:

Answer 35

1. lag phase
2. exponential (log) phase
3. stationary phase
4. death phase

• The bacteria adapt to new local conditions during the lag phase.
• Growth then increases exponentially during the exponential (log) phase.
• As resources are reduced, growth levels off during the stationary phase.
• As resources are depleted, bacteria undergo a death phase.

Question 36

Viruses and Subviral Particles chapter

Answer 36

START

Question 37

Viruses contain

Answer 37

1. Nucleic acid
2. Captid (protein coat)
3. Tail sheath
4. Tail fiber
5. Sometimes an envelope

Viruses contain genetic material, a protein coat (capsid), and sometimes a lipid-containing envelope.

An envelope is sensitive to heat, detergent, and desiccation. hence, easy to kill.

If no envelope than it would be hard to kill.

Question 38

Viruses are obligate intracellular parasites, meaning that they

Answer 38

Viruses are obligate intracellular parasites, meaning that they cannot survive and replicate outside of a host cell. Individual virus particles are called virions.

Question 39

Bacteriophages are

Answer 39

Bacteriophages are viruses that target bacteria. In addition to the other structures, they contain a tail sheath, which injects the genetic material into a bacterium, and tail fibers, which allow the bacteriophage to attach to the host cell.

Question 40

Viral genomes may be made of various nucleic acids:

Answer 40

• They may be composed of DNA or RNA and may be single-or double-stranded.
• Single-stranded RNA viruses may be positive sense (that can be translated by the host cell) or negative sense (which requires a complementary strand to be synthesized by RNA replicase before translation).
• Retroviruses contain a single-stranded RNA genome, from which a comple-mentary DNA strand is made using reverse transcriptase. The DNA strand can then be integrated into the genome.

Question 41

Viruses infect cells by

Answer 41

Viruses infect cells by attaching to specific receptors, and can then enter the cell by fusing with the plasma membrane, being brought in by endocytosis, or injecting their genome into the cell.

Question 42

The virus reproduces by

Answer 42

The virus reproduces by replicating and translating genetic material using the host cell’s ribosomes, tRNA, amino acids, and enzymes.

Question 43

Viral progeny are released through

Answer 43

• Viral progeny are released through cell death, lysis, or extrusion.

Question 44

Bacteriophages have two specific life cycles:

Answer 44

1. Lytic cycle
2. Lysogenic cycle

• In the lytic cycle, the bacteriophage produces massive numbers of new virions until the cell lyses. Bacteria in the lytic phase are termed virulent.
• In the lysogenic cycle, the virus integrates into the host genome as a provirus or prophage, which can then reproduce along with the cell. The provirus can remain in the genome indefinitely, or may leave the genome in response to a stimulus and enter the lytic cycle.

Question 45

Prions are

Answer 45

Prions are infectious proteins that trigger misfolding of other proteins, usually converting an α-helical structure to a β-pleated sheet. This decreases the solubility of the protein and increases its resistance to degradation.

Question 46

Viroids are

Answer 46

Viroids are plant pathogens that are small circles of complementary RNA that can turn off genes, resulting in metabolic and structural changes and, potentially, cell death.

ex of viroids in humans; hepatitid D (HDV)

Question 47

Plasmids that can integrate into genome are called

Answer 47

Episomes

Question 48

The lysoginic cycle

Answer 48

This type of gene transfer of viral DNA

Question 49

positive sense vs negative sense

Answer 49

positive-sense implies that the genome may be directly translated to functional proteins by the ribosomes of the host cell, just like mRNA.

negative-sense RNA viruses are a bit more complicated; the negative sense RNA strand acts as a templet for symthesis if a complementray 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 complementary strand is synthesized.

—————— (- RNA)

——————(+RNA)

Question 50

HIV is what?

Answer 50

is a retrovirus that utilizes this life cycle(reverse transcriptase), which is one of the characteristics that make HIV so difficult to treat

Question 51

there are 4 tissue types:

Answer 51

epithelial tissue

connective tissue

muscle tissue

nervous tissue

Question 52

bec viruses cannot reproduce independently they are considered what?

Answer 52

obligate intracellular parasites

Question 53

viruses will replicate and produce viral progeny called

Answer 53

virions