MCAT Biology Review - Chapter 1: The Cell

Question 1

1.1 Cell Theory

How many cells are in the human body and how much do bacterial cells out number the eukaryotic cells?

Answer 1

37 trillion cells and they outnumber them 10 to 1.

Question 2

What was believed in the 1600s about organisms and why?

Answer 2

They were perceived to being complete and inseparable into smaller parts.

Due to the inability to see smaller structures through simple optical instruments.

Question 3

Who, in 1665, assemble a crude microscope and tested its properties on a piece of cork?

Answer 3

Robert Hooke (known for Hooke’s Law, characterization of springs)

Question 4

What did Robert Hooke compare the honeycomb-like like structures within the cork using his crude microscope?

Answer 4

Small rooms within a monastery, known as cells.

Question 5

Who, and when, saw the first living cell under a microscope in 1674?

Answer 5

Anton von Leeuwenhoek

Question 6

What did Rudolph Virchow demonstrate in 1850?

Answer 6

That diseased cells arise from normal cells in normal tissues.

Question 7

What were the three original basic tenets of cell theory?

Through the advances of molecular biology, what is the fourth tenet?

Answer 7

1. All living things are composed of cells.
2. The cell is the basic functional unit of life.
3. Cells arise only from preexisting cells.
4. Cells carry genetic information in the form of deoxyribonucleic acid (DNA). Genetic material is passed on from parent to daughter cell.

Question 8

What tenets are violated by viruses and virions and why?

Answer 8

The third and fourth tenets.

They replicate by invading other organisms and because they use RNA as their genetic information.

Question 9

1.2 Eukaryotic Cells

What is the first major distinction we can make between living organisms?

Answer 9

If they are composed of prokaryotic or eukaryotic cells.

Question 10

T/F Prokaryotic organisms are always acellular, while eukaryotic organisms are always multicellular and unicellular.

Answer 10

False.

Prokaryotic organisms are ALWAYS single-celled, while eukaryotic organisms can be unicellular or multicellular.

Viruses are acellular since they lack most components of a cell.

Question 11

What type of cell contains a nucleus enclosed in a membrane?

What cell does not have a nucleus?

Answer 11

Eukaryotic cells

Prokaryotic cells

Question 12

What allows for compartmentalization of function of organelles within a cell?

Answer 12

They are membrane-bound isolating them from the cytosol.

Question 13

What allow for diffusion of molecules throughout the cell?

Answer 13

The cytosol

Question 14

Where is the genetic material encoded in deoxyribonucleic acid (DNA) and how is this DNA organized?

Answer 14

In the nucleus, and it is organized into chromosomes. ALL genetic material necessary to replicate the cell is located in the nucleus.

Question 15

How do eukaryotic cells reproduce? And what do they produce when reproducing?

Answer 15

Mitosis, and allows the formation of two identical daughter cells.

Question 16

• What is the difference between the cytoplasm and the cytosol?*

Answer 16

Cytoplasm includes all structures and organelles within a cell. The cytosol is the fluid within the cell, and everything floats in it!

Question 17

What is the nucleus surrounded by? And what does it maintain?

Answer 17

It is surrounded by the nuclear membrane or envelope. It is a double membrane that maintains a nuclear environment separate and distinct from the cytoplasm.

Question 18

What, within the nuclear membrane or envelope, allows for a selective two-way exchange of material between the cytoplasm and the nucleus?

Answer 18

The nuclear pores.

Question 19

What are the coding regions of DNA?

Answer 19

Genes.

Question 20

What is linear DNA wound around? After being wound, what it is further wound into?

Answer 20

Organizing proteins called histones. Linear strands called chromosomes.

Question 21

What does the location of DNA in the nucleus permit in relation to transcription and translation?

Answer 21

It permits the compartmentalization of DNA transcription separate from RNA translation.

Transcription of mRNA (from hnRNA) to translation (mRNA to peptides)

hnRNA stands for heterogeneous nuclear RNA. It refers to the large pre‐mRNAs of various nucleotide sequences that are made by RNA Polymerase II, and processed in the nucleus to become cytoplasmic mRNAs. RNA Capping RNA Polymerase II Transcription.

Question 22

What does the subsection of the nucleus, known as the nucleolus (takes up roughly 25% of the volume of the nucleus and can often be identified as a darker spot in the nucleus), synthesize what?

Answer 22

Ribosomal RNA (rRNA)

Question 23

What is often called the power plants of the cell, in reference to their important metabolic functions?

Answer 23

Mitochondria (plural) Mitochondrion (singular)

Question 24

How many layers does a mitochondrion consist of and what are their purpose?

Answer 24

2.

The outer membrane serves as a barrier between the cytosol and the inner environment of the mitochondrion.

The inner membrane contains the molecules and enzymes of the eletron transport chain (ETC).

Question 25

What are the numerous infoldings in which the inner membrane of the mitochondrion is arranged?

Why are they arranged this way?

Answer 25

Cristae.

These highly convoluted structures that increase the surface area available for electron transport chain enzymes.

Question 26

What do you call the space between the inner and outer membrane of the mitochondrion?

What do you call the space inside the inner membrane of the mitochondrion?

Answer 26

Intermembrane space

Mitochondrial matrix

Question 27

Real World (No Answer)

The serial endosymbiosis (a symbiotic relationship where one organism lives inside the other) theory attempts to explain the formation of some of the membrane-bound organelles; it posits that these organelles formed by the engulfing of one prokaryote by another and the establishment of a symbiotic relationship. In addition to mitochondria, chloroplasts in plant cells and organelles of motility (such as flagella) are believed to originated from this process.

Bottom line: Mitochondria are thought to have originated when the engulfing of an aerobic prokaryote by an anaerobic prokaryote resulted in a symbiotic relationship.

Answer 27

(No Answer)

Question 28

What establishes the proton-motive force?

Answer 28

The pumping of protons from the mitochondrial matrix to the intermembrane space; ultimately, these protons flow through ATP synthase to generate ATP during oxidative phosphorylation.

Question 29

Why are mitochondria different from other parts of a cell and what do they contain?

Answer 29

They are semi-autonomous. They contain some of their own genes and replicate independently of the nucleus via binary fission.

Question 30

Why are mitochondria considered semi-autonomous?

Answer 30

They are only semi-autonomous because the replication, transcription and translation of the DNA molecules within the mitochondrion, mtDNA, are ultimately controlled by the cell nucleus.

Question 31

What is a typical or paradigmatic example of cytoplasmic or extranuclear inheritance?

Answer 31

The transmission of genetic matieral independent of the nucleus.

Question 32

In addition to keeping the cell alive by providing energy, the mitochondria are also capable of killing the cell by release of enzymes from the ETC. What process does this release of enzymes kick-start? Also known as programmed cell death.

Answer 32

Apoptosis

Question 33

What are the membrane-bound structures that contain hydrolytic enzymes (acts and behaves like hydrolase) that are capable of breaking down many different substrates, including substances ingested by endocytosis (taking in matter by a living cell via invagination) and cellular waste products?

Answer 33

Lysosomes

Question 34

What do lysosomes often function in conjuntion with that transports, packages, and sorts cell materials to and from the membrane?

They are capable of transporting materials to the trans-golgi, to the cell membrane, or to the lysosomal pathway for degradation.

Answer 34

Endosomes

Question 35

Why does the lysosomal membrane sequester its enzymes? And what is the process called when the enzymes are released?

Answer 35

To prevent damage to the cell. The process is called autolysis and, like mitochondria, their hydrolytic enzymes are released which results in apoptosis if the cell when cellular components are degraded.

Question 36

What is a series of interconnected membranes that are actually contigous with the nuclear envelope, has a double membrane that is folded by numerous invaginations creating complex structures with a central lumen (inside space of a tubular structure similar to a vein or artery)?

Answer 36

Endoplasmic reticulum

Question 37

What is studded with ribosomes within a cell and what do they permit?

Answer 37

RER. The ribosomes permit the translation of proteins destined for secretion directly into its lumen.

Question 38

What lacks ribosomes, and is utilized primarily for lipid sysnthesis (such as the phospholipids in the cell membrane) and the detoxification of certain drugs or poisons?

Answer 38

SER. This structure also transports proteins from the RER to the Golgi apparatus.

Question 39

What consists of stacked membrane-bound sacs where materials are transferred to in vesicles?

Answer 39

Golgi apparatus

Question 40

What happens to the materials once inside the golgi apparatus?

Answer 40

They are be modified by the addition of groups like carbohydrates, phosphates, and sulfates.

The GA may also modify cellular products through introduction of signal sequences, which direct the delivery of the product to a specific cellular location.

Question 41

What happens after the modification and sorting of the products within the GA? What happens if the cellular products are destined for secretion?

Answer 41

They are packaged in vesicles and directed to the correct cellular location. If destined for secretion, the secretory vescile merges with the cell membrane and its contents are released via exocytosis (opposite of endocytosis).

Question 42

What cellular component contains hydrogen peroxide, and has a primary function to breakdown very long chain fatty acids via B-oxidation?

Answer 42

Perioxisomes. They also participate in the synthesis of phospholipids and contain some of the enzymes involved in the pentose phosphate pathway.

Question 43

Give 2 examples of cells not having the same distribution of organelles? Form will follow function.

Answer 43

Cells that require a lot of energy for locomotion (such as sperm cells) have high concentrations of mitochondria.

Cells involves in secretion (such as pancreatic islet cells and other endocrine tissues) have high concentrations of RER and Golgi apparatuses.

Other cells, such as red blood cells, which primarily serve a transport function, have no organelles at all.

Question 44

What provides structure to the cell and helps it maintain its shape? It also provides a conduit for the transport of materials around the cell.

Answer 44

Cytoskeleton.

Question 45

What are the three components of the cytoskeleton?

Answer 45

Microfilaments, microtubules, and intermediate filaments.

Question 46

What component of the cytoskeleton is made up of solid polymerized rods of actin where the actin filaments are organized into buncdles and networks resistant to both compression and fracture which provides protection for the cell?

Answer 46

Microfilaments

Question 47

Which component of the cytoskeleton can use ATP to generate force for movement by interacting with myosin, such as muscle contraction?

Answer 47

Microfilaments or actin filaments.

Question 48

Which component of the cytoskeleton also plays a role in cytokinesis, or the division of materials between daughter cells during mitosis?

Answer 48

Microfilaments

The cleavage furrow is formed from microfilaments, which organize as a ring at the site of division between the two new daughter cells. As the actin filaments within this ring contract, the ring becomes smaller, eventually pinching off the connection between daughter cells.

Question 49

What component of the cytoskeleton are hollow polymers of tubulin proteins which radiate throughout the cell, providing primary pathways along which moto proteins like kinesin and dynein carry vesicles?

Answer 49

Microtubules

Question 50

What are the motile structures composed of microtubules?

Answer 50

Cilia and flagella

Question 51

What is the difference between cilia and flagella even though they have the same structure?

Answer 51

Cilia are projections from a cell that are primarily involved in the movement of materials along the surface of the cell like the lining of the respiratory tract and the movement of mucus.

Flagella are structures involved in the movement of the cell itself, such as the movement of sperm cells through the reproductive tract.

Question 52

Anatomically, what are cilia and flagella composed of?

Answer 52

9 pairs of microtubles forming an outer ring, with two microtubules in the center. This is known as a 9 + 2 structure and is seen ONLY in eukaryotic organelles of motility. Bacteria have a different structure with a different chemical composition.

Question 53

What can be found in a region of cell called the centrosome?

Answer 53

Centrioles

Question 54

How are centrioles within the centrosomes structured and what is their purpose?

Answer 54

They are the organizing centers for microtubules and are structured as 9 triplets (not pairs) of microtubules with a hollow center.

Question 55

What is the role of the centrioles during mitosis?

Answer 55

They migrate to opposite sides of the dividing cell and organize the mitotic spindle.

Question 56

What do the microtubules emanating from the centrioles accomplish?

Answer 56

They attach to the chromosomes via complexes called kinetochores and exert force on the sister chromatids, pulling them apart.

Question 57

What are a diverse group of filamentous proteins, which includes keratin, desmin, vimentin, and lamins?

Answer 57

Intermediate filaments

Question 58

What are many intermediate filaments involved in?

Answer 58

Cell to cell adhesion or maintenance of the overall integrity of the cytoskeleton.

They are able to withstand a tremondous amount of tension, increasing the structural rigidity of the cell. In addition, intermediate filaments help anchor other organelles, including the nucleus.

Question 59

What are the identity of the intermediate filaments proteins within a cell dependent upon?

Answer 59

Specific to the cell and tissue type

Question 60

What do you call the unique characteristic whereas different eukaryotic cells within a tissue may carry out different functions?

Answer 60

Division of labor

Question 61

What are the four types of tissue?

Answer 61

Epithelial tissue, connective tissue, muscles tissue, and nervous tissue.

Question 62

What type of tissue covers the body and its cavities, providing a means for protection against pathogen invasion and desiccation? These cells WITHIN organs can be involved with absorption, secretion, and sensation.

Answer 62

Epithelial tissue.

Question 63

Other than attaching tightly to each other, what else do epithelial cells attach to?

Answer 63

To underlying connective tissue called the basement membrane.

Question 64

In most organs, epithelial cells constitute as what since these cells can serve many functions depending on the identity of the organ?

Answer 64

Constitute the parenchyma, or the functional parts of the organ.

Question 65

What are examples of the parenchyma for the kidneys, liver, and stomach?

Answer 65

The nephrons in the kidney are composed of epithelial cells, hepatocytes in the liver, and acid-producing cells of the stomach.

Question 66

How are the different epithelia LAYERS classified?

Answer 66

Simple epithelia have one layer of cells.
Stratified epithelia have multiple layers.
Pseudostratified epithelia appear to have multiple layers due to differences in cell height but are, in reality, only one layer.

Question 67

How are the different epithelia SHAPES classified?

Answer 67

Cubodial cells are cube-shaped.
Columnar cells are long and thing.
Squamous cells are flat and scale like.

Question 68

What supports the body and provides a framework for the epithelial cells to carry out their function?

Answer 68

Connective tissue.

Question 69

Whereas epithelial cells contribute to the parenchyma of an organ, connective tissues are the main contributors to the _ _ _ _ _ or support structure.

Answer 69

Stroma

Question 70

What are examples of connective tissue?

Answer 70

Bone, cartilage, tendons, ligaments, adipose tissue, and blood are all examples of connective tissue.

Question 71

Why do most cells in connective tissues produce and secrete materials such as collagen and elastin?

Answer 71

The extracellular matrix (the areas between the cells)

Question 72

Prokaryotes are the simplest of all organisms and include all bacteria. Prokaryotes do not contain any membrane-bound organelles, and their genetic material is organized into a single-circular molecule of DNA concentrated in an area of the cell called?

Answer 72

Nucleoid region.

Question 73

What are the three domains in which all life is classfied?

Answer 73

Archaea, Bacteria, and Eukarya.

Archaea and bacteria contain prokaryotes.

Question 74

T/F Archaea, single-celled organisms, are visually more similar to Eukarya than Bacteria.

Answer 74

False. Archaea are visually more similar to bacteria, but contain genes and several metabolic pathways that are more similar to eukaryotes.

Question 75

What is a word for Archaea that can withstand harsh environments with extremely high temperatures, high salinity, or no light?

Answer 75

Extremophile. They are also notables for their ability to use alternative sources of energy such as photosynthesis and chemosynthesis which allows them to generate energy from inorganic compounds like sulfur- and nitrogen-based compounds such as ammonia.

Question 76

Fun Fact (No Answer)

Due to the similarities of this domain to eukaryotes, it is hypothesized that eukaryotes and the Archaea share a common origin. Both eukaryotes and Archaea start translation with methionine, contain similar RNA polymerases, and associate their DNA with histones.

However, Archaea contain a single circular chromosome, divide by binary fission or budding, and share a similar overall structure to bacteria. Interestingly, Archaea are resistant to many antibiotics.

Answer 76

No Answer

Question 77

Name all the structures that all bacteria have (3)

Answer 77

1. cell membrane
2. cytoplasm
3. flagella or fimbriae (similar to cilia)

Question 78

What type of relationship exists where both organisms benefit?

Answer 78

Mutualistic symbiotes.

Example include the bacteria in the human gut that produce vitamin K and biotin (vitamin B7), and which also prevent the overgrowth of harmful bacteria.

Question 79

What does parasite or pathogen mean?

Answer 79

It means they provide no advantage or benefit to the host, but rather cause disease.

Question 80

What does it mean that pathogenic bacteria can live intracellularly and extracellularly?

Answer 80

Either within or outside the cell. Chlamydia trachomatic, an STD lives inside cells of the reproductive tract. Clostridium tetani, the cause of tetanus, lives outside of cells and produces toxins that enter the bloodstream.

Question 81

What is classification of bacteria by shape so important?

Answer 81

It helps scientists and pathologists a common language to talk about bacteria, as well as to identify different species of bacteria.

Question 82

What are the three shapes that most bacteria exist?

Answer 82

Cocci - spherical bacteria like Streptococcus pyogenes
Bacilli - rod-shaped bacteria like Escherichia coli
Spirilli - spiral-shaped bacteria like Treponema pallidum

Question 83

Real World Fact (No Answer)

Bacteria perform essential functions for human beings, including the production of vitamin K in the intestine. Vitamin K is required for production of the plasma proteins necessary for blood clotting. Newborn infants are not yet colonized by bacteria and cannot produce clotting factors, putting them at risk of hemorrhage. When babies are born, they are given an injection of vitamin K to aid in the production of clotting factors until they have been colonized with bacteria.

Answer 83

No Answer

Question 84

Real World Fact (No Answer)

Very few pathogenic bacteria are spiral shaped. The three most common are:

• Treponema pallidum, the cause of syphilis
• Borrelia burgdorferi, the cause of Lyme disease
• Leptospira interrogans, the cause of Weil’s disease

Answer 84

No Answer

Question 85

What do you call bacteria that require oxygen for metabolism?

Answer 85

Obligate aerobes

Question 86

What do you call bacteria that use fermentation, or some other form of cellular metabolism that does not require oxygen?

Answer 86

Anaerobes

Question 87

What do you call anaerobes that cannot survive in an oxygen-containing environment?

Answer 87

Obligate anaerobes.

The presence of oxygen leads to the production of reactive-oxygen containing radicals in this species, which leads to cell death.

Question 88

What are facultative anaerobes?

Answer 88

They are bacteria capable of toggling between metabolic processes, using oxygen for aerobic metabolism if is present, and switching to anaerobic metabolism if it is not.

Question 89

What are bacteria that are unable to use oxygen for metabolism, but are not harmed by its presence in the environment?

Answer 89

Aerotolerant anaerobes

Question 90

What are some of the main differences between prokaryotes and eukaryotes?

Answer 90

1. Prokaryotes lack a nucleus and membrane-bound organelles.
2. Single-celled organisms, meaning that each cell must be able to perform all of the functions necessary for life on its own.
3. They may, however, live in colones with other cells and may signal these cells to share information about the environment.

Question 91

What is the outer and inner wall of a bacterium or prokaryote?

Answer 91

Cell wall is the outer layer, and the cell (or plasma) membrane, which is composed of phospholipids, is the inner wall.

Question 92

What does the cell wall and the cell membrane make up?

Answer 92

The envelope of the cell.

Question 93

What provides the structure and controls the movement of solutes into and out of the bacterium which allows the cell to maintain a concentration gradient relative to the environment?

Answer 93

The cell wall of the organism

Question 94

What are the two types of cell walls?

Answer 94

Gram positive and gram negative.

Question 95

How is the type of cell wall determined?

Answer 95

By a Gram staining process…

A crystal violet stain, followed by counterstain with a substance called safranin.

If the envelope absorbs the crystal violet stain, it will appear deep purple, and cell is said to be gram positive.

If the envelope does not absorb the crystal violet stain, but absorbs the safranin counterstain, then the cell will appear pink-red, and the cell is said be gram negative.

Question 96

What type of cell wall consists of a thick layer of peptidoglycan which aids a bacterial pathogen by providing protection from a host organism’s immune system? This cell wall also contains lipoteichoic acid which may activate the human immune system by exposure to these chemials?

Answer 96

Gram-positive cell wall.

Question 97

What type of cell wall is very thin and contains small amounts of peptidoglycan? The peptidoglycan cell walls of these bacteria are adjacent to the cell membrane, and are separated from the membrane by the periplasmic space.

Answer 97

Gram-negative cell wall.

In addition to the cell wall and cell membrane, gram-negative bacteria also have outer membranes containing phospholipids and lipopolysaccharides. These saccharides are the part of gram-negative bacteria that triggers an immune response in human beings; the inflammatory response to lipopolysaccharides is much stronger than the response to lipoteichoic acid.

Question 98

Real World: What does the antibiotic penicillin target within gram-positive bacteria like streptococcus (strep throat) and treponema (syphilis)?

Answer 98

The enzyme that catalyzes the cross-linking of peptidoglycan within cell walls. If this cross-linking cannot happen, the cell wall no longer protects the bacterium.

Question 99

What is the ability of a cell to detect chemical stimuli and move toward or away from them is called?

Answer 99

Chemotaxis

Question 100

What is a flagellum composed of?

Answer 100

A filament, a basal body, and a hook.

Similar for both gram-positive and gram-negative bacteria but differ slightly due to the chemical composition and physical structure of the envelope. Archaea also contain flagella but it is much different from that of bacteria.

Question 101

What is a hollow, helical structure composed of flagellin?

Answer 101

A filament

Question 102

What is a complex structure that anchors the flagellum to the cytoplasmic membrane and is also the motor of the flagellum, which rotates at rates up to 300 hz?

Answer 102

The basal body

Question 103

What connects the filament and the basal body so that, as the basal body rotates, it exerts torque on the filament, which thereby spins and propels the bacterium forward?

Answer 103

The hook.

Question 104

What is DNA acquired from external sources may also be carried on smaller circular structures known as?

Answer 104

Plasmids.

They carry DNA that is not necessary for survival of the prokaryote–and therefore is not considered part of the genome of the bacterium–but may confer an advantage such as antibiotic resistance.

Question 105

True/False Prokaryotes lack several key organelles, such as mitochondria.

Answer 105

True

Question 106

How do prokaryotes generate ATP?

Answer 106

They utilize their cell membrane for the electron transport chain and generation of ATP.

They also contain less primitive cytoskeleton, and not nearly as complex as the one found in eukaryotes.

Prokaryotes also contain ribosomes, but this ribosome is a different size from that found in eukaryotes: prokaryotic ribosomes contain 30S and 50S subunits, whereas eukaryotic ribosomes contain 40S and 60S ribosomes.

Since prokaryotes and eukaryotes have different sized ribosomes, it is implied they carry out protein synthesis in different ways. This difference also allows us to target bacterial ribosomes with a number of antibiotics, including tetracyclines, aminoglycosides, and macrolides, while leaving the eukaryotic ribosome more or less unaffected.

Question 107

What is a simple form of asexual reproduction seen in prokaryotes where the circular chromosome attaches to the cell wall and replicates while the cell continues to grow in size where, eventually, the plasma membrane and cell wall begin to grow inward along the midline of the cell to produce two identical daughter cells?

Answer 107

Binary fission.

Since BF requires fewer events than mitosis, it can proceed more rapidly. In fact, some strains of E. coli can replicate every 20 minutes under ideal growth conditions.

Question 108

What is the extrachromosomal (extragenomic) material found within bacteria?

Answer 108

Plasmids

These typically carry genes that impart some benefit to the bacterium, such as antibiotic resistance, antibiotic degrading enzyme or altering enzyme, etc.

Question 109

Plasmids may carry additional virulence factors, what does this mean?

Answer 109

These are traits that increase pathogenicity, such as toxin production, projections that allow attachment to certain kinds of cells, or features that allow evasion of the host’s immune system.

Question 110

What is a subset of plasmids that are capable of integrating into the genome of the bacterium?

Answer 110

Episomes

Question 111

What does bacterial genetic recombination help?

Answer 111

It helps to increase bacterial diversity and thus permits evolution of a bacterial species over time.

Question 112

What are the three recombination processes among bacteria?

Answer 112

Transformation, conjugation, and transduction.

Question 113

What type of genetic recombination results from the integration of foreign genetic material into the host genome which most frequently comes from other bacteria that, upon lysing, spill their contents into the vicinity of a bacterium capable of this technique?

Answer 113

Transformation.

Many gram-negative rods are able to carry our this process.

Question 114

What type of genetic recombination is the bacterial form of mating (sexual reproduction) where it involves two cells forming a ??? bridge between them that facilitates the transfer of genetic material?

Answer 114

Conjugation and the conjugation bridge.

The bridge is made from appendages called sex pili that are found on the donor male (+).

Question 115

For conjugation, is the transfer direction unidirectional or bidirectional? And how are the two cells labeled in respect of the flow of genetic material?

Answer 115

It is unidirectional meaning one direction, and the donor male (+) to the recipient female (-).

Question 116

For conjugation, in order for the donor male (+) to form the sex pilus, what type of plasmids must it contain to have the necessary genes?

Answer 116

Sex factors.

Question 117

What is the best studied sex factor within bacteria where the bacteria possessing this plasmid are termed F+ cells; those without are called F- cells?

Answer 117

F (fertility) factor in E. coli.

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 the 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.

Question 118

What does it mean to say cells have undergone a change referred to the abbreviation Hfr (High frequency of recombination)?

Answer 118

The sex factor in a plasmid can be integrated into the genome of the host via transformation. When conjugation finally occurs, the entire genome replicates because it now contains the sex factor which then the donor cell will attempt to transfer an entire copy of its genome to the recipient cell; however, the conjugation bridge usually breaks before the full DNA sequence can be moved.

Question 119

What is the only genetic recombination process that requires a vector–a virus that carries genetic material from one bacterium to another?

Answer 119

Transduction.

Remember: viruses are obligate intracellular pathogens, which means that they cannot reproduce outside of a host cell.

Question 120

What are viruses that infect bacteria and can accidentally incorporate a segment of host DNA during assembly?

Answer 120

A bacteriophage

When infecting another bacterium, it can release this trapped DNA into the new host cell. This transferred DNA can then integrate into the genome, giving the new host additioanl genes.

Question 121

What are genetic elements capable of inserting and removing themselves from the genome; a phenomenon is not limited to prokaryotes but has been seen in eukaryotes as well?

Answer 121

Transposons.

If a transposon is inserted within a coding region of a gene, that gene may be disrupted.

Question 122

In bacterial reproduction, what are the 4 phases of growth?

Answer 122

Lag phase - bacteria adapt to new environment

Exponential phase (aka log phase) - as bacteria adapt, the rate of division increases, causing exponential increase in the number of bacteria in the colony

Stationary phase - the reduction of resources slow reproduction, which results in this phase

Death phase - after bacteria have exceeded the ability of the environment to support the number of bacteria, this phase occurs, marking the depletion of resources

Question 123

What phase within reproduction of bacteria does the resources begin to fall dramatically?

Answer 123

The exponential phase

Question 124

What are viruses composed of?

Answer 124

Genetic material, a protein coat, and sometimes an envelope containing lipids.

Question 125

How is the genetic material in viruses physically shaped and what are they composed of?

Answer 125

Circular or linear, single- or double-stranded, and composed of either DNA or RNA.

Question 126

What is the protein coat known as, which may be surrounded by an envelope composed of phospholipids and virus-specific proteins?

Answer 126

A capsid

Question 127

T/F Enveloped viruses are easier to kill.

Answer 127

True. The envelope is very sensitive to heat, detergents, and dessication; thus, enveloped viruses are easier to kill.

On the other hand, viruses that do not have an envelope are more resistant to sterilization and are likely to persist on surfaces for an extended period of time.

Question 128

Why are viruses considered obligate intracellular parasites?

Answer 128

Because they cannot reproduce independently

Viruses must express and replicate genetic information within a host cell because they lack ribosomes to carry out protein synthesis.

Question 129

What are the replicated and produced viral progeny called when a virus hijacks the host cells machinery?

Answer 129

Virions. These can be released to infect additional cells.

Question 130

What are viruses that specfically target bacteria?

Answer 130

Bacteriophages

They do not actually enter the bacteria; rather, they simply inject their genetic material, leaving the remaining structures outside the infected cell.

Question 131

What about a bacteriophage allow them to:

1. Act like a syringe, injecting genetic material into a bacterium
2. Help the bacteriophage recognize and connect to the correct host cell

Answer 131

The tail sheath and tail fibers.

Question 132

What is the difference between a positive sense single strand RNA virus and a negative sense single strand RNA virus?

Answer 132

Positive-sense RNA viruses 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 in that the negative sense strand acts as a template for synthesis of a complementary strand, which can then be used as a template for protein synthesis.

Question 133

What must Negative-sense RNA viruses carry in the virion to ensure that the complementary strand is synthesized?

Answer 133

RNA replicase

Question 134

What are enveloped, single-stranded RNA viruses in the family Retroviridae; usually, the virion contains two identical RNA molecules and carries an enzyme known as reverse transcriptase?

Answer 134

Retroviruses

Question 135

What does reverse transcriptase allow a retrovirus to accomplish?

Answer 135

Allows synthesis of DNA from single-stranded RNA

Question 136

Why are retroviruses so dangerous?

Answer 136

Because when the DNA created by reverse transcriptase enzyme is integrated in the host cell’s genome, it then begins to be replicated and transcribed as if it were the host cell’s own DNA.

This is a clever mechanism because the integration of the genetic material into the host cell genome allows the cell to be infected indefinitely, so the only way to remove the infection is to kill the infected cell.

Question 137

What is a very popularized retrovirus?

Answer 137

The human immunodeficiency virus (HIV) is a retrovirus that utilizes the life cycle of imprinting its genome within the host’s genome, which makes it so difficult to treat.

Question 138

T/F Viruses can infect any type of cells.

Answer 138

False. They can infect cells with certain surface receptors. Without specfic receptors, the cells are invisible to the virus.

Question 139

What are the two ways viruses infect cells?

Answer 139

Enveloped viruses such as HIV fuse with the membrane and enter the cell intact, whereas bacterophages only insert their genetic material, leaving their capsids outside the cell.

Question 140

What do most DNA viruses need to happen in order to be transcribed into mRNA?

Answer 140

It must be translocated to the correct location within the host cell (most cases the nucleus) and from there, it is released into the cytoplasm and translated into proteins.

Genetic material from positive-sense RNA viruses stays in the cytoplasm, where it is directly translated into protein by host cell ribosomes.

Negative-sense RNA viruses require synthesis of a complimentary RNA strand via RNA replicase, which can then be translated to form proteins.

DNA formed through reverse transcription in retroviruses also travels to the nucleus, where it can be integrated into the host genome.

Question 141

What are most of the proteins created by virions once hyjacking is complete?

Answer 141

Structural capsid proteins which allow for the creation of new virions in the cytoplasm in the host cell. Once completely replicated, it can be packaged within a capsid.

Note that the viral genome MUST BE returned to its original form before packaging; for example, retroviruses must transcribe new copies of their single-stranded RNA from the DNA that entered the host genome.

A single virus may create anywhere from hundereds to many thousands of new virions within a single host cell.

Question 142

What are the two general ideas of viral progeny release? (3)

Answer 142

1. Viral invasion initiates cell death resulting in the spillage of progeny
2. Host cell may lyse due to being filled with extremely large numbers of virions
3. A virus can leave the cell by fusing with its plasma membrane

Question 143

Why is lysis of a host cell a disadvantage to a virion?

Answer 143

The virus can no longer use the cell to carry out its life cycle.

Question 144

What is known as extrusion?

Answer 144

When a virus melds with the host’s membrane and buds into the environment. This process keeps the host cell alive, and thus allows for the continued use of the host cell by the virus.

A virus in this state is said to be in a productive cycle.

Question 145

What determines if a bacteriophage enters a lytic or lysogenic life cycle? These two phases are similar to the lysis and productive cycle methods of progeny release.

Answer 145

It depends on growth conditions and the specific virus.

Question 146

What life cycle of a bacteriophage maximizes the use of the cell’s machinery with little regard for the survival of the host cell?

Answer 146

Lytic cycle.

Once the host is swollen with new virions, the cell lyses, and other bacteria can be infected.

Question 147

What are viruses in the lytic phase termed as?

Answer 147

Virulent

Question 148

What life cycle of a bacteriophage consists of the virus not lysing the bacterium, but integrates into the host genome as a provirus or prophage?

Answer 148

Lysogenic cycle

The virus is now replicated because it is now a part of the host’s genome.

Question 149

Even though the bacteriophage is integrated as a provirus or prophage, what can cause it to leave the lysogenic phase and begin a lytic phase?

Answer 149

Environmental factors such as radiation, light, or chemicals can cause it to enter a lytic phase.

The prophage may extract bacterial DNA as it leaves the genome, which allows transduction of genes from one bacterium to another.

Question 150

Why might it be an advantage if a phage integrates with a host genome even though it could kill it?

Answer 150

Infection of one strain of phage generally makes the bacterium less susceptible to superinfection (simultaneous infection) with other phages. Because the provirus is relatively innocuous, the arrangement many confer an evolutionary advantage.

Question 151

What are, generally, prions and viroids?

Answer 151

Very small (subviral) particles that can cause disease under certain circunstances.

Question 152

What are infectious proteins that cause disease by triggering misfolding of other proteins, usually through the conversion of a protein from an a-helical structure to a B-pleated sheet?

Answer 152

Prions.

This drastically reduces the solubility of the protein, as well as the ability of the cell to degrade the protein. Eventually, protein aggregates form, interfering with cell function.

These are known to cause bovine spongiform encephalopathy (mad cow disease), Creutzfeldt-Jakob disease, and familial fatal insomnia in humans.

Question 153

What are small pathogens consisting of a very short circular single-stranded RNA that infect plants?

Answer 153

Viroids

Viroids can bind to a large number of RNA sequences and can silence genes in the plant genome. This prevents synthesis of necessary proteins, resulting in metabolic disruption and structural damage to the cell.