MCAT Biology Review - Chapter 1: The Cell Flashcards
1
Q
1.1 Cell Theory
How many cells are in the human body and how much do bacterial cells out number the eukaryotic cells?
A
37 trillion cells and they outnumber them 10 to 1.
2
Q
What was believed in the 1600s about organisms and why?
A
They were perceived to being complete and inseparable into smaller parts.
Due to the inability to see smaller structures through simple optical instruments.
3
Q
Who, in 1665, assemble a crude microscope and tested its properties on a piece of cork?
A
Robert Hooke (known for Hooke’s Law, characterization of springs)
4
Q
What did Robert Hooke compare the honeycomb-like like structures within the cork using his crude microscope?
A
Small rooms within a monastery, known as cells.
5
Q
Who, and when, saw the first living cell under a microscope in 1674?
A
Anton von Leeuwenhoek
6
Q
What did Rudolph Virchow demonstrate in 1850?
A
That diseased cells arise from normal cells in normal tissues.
7
Q
What were the three original basic tenets of cell theory?
Through the advances of molecular biology, what is the fourth tenet?
A
- 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 deoxyribonucleic acid (DNA). Genetic material is passed on from parent to daughter cell.
8
Q
What tenets are violated by viruses and virions and why?
A
The third and fourth tenets.
They replicate by invading other organisms and because they use RNA as their genetic information.
9
Q
1.2 Eukaryotic Cells
What is the first major distinction we can make between living organisms?
A
If they are composed of prokaryotic or eukaryotic cells.
10
Q
T/F Prokaryotic organisms are always acellular, while eukaryotic organisms are always multicellular and unicellular.
A
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.
11
Q
What type of cell contains a nucleus enclosed in a membrane?
What cell does not have a nucleus?
A
Eukaryotic cells
Prokaryotic cells
12
Q
What allows for compartmentalization of function of organelles within a cell?
A
They are membrane-bound isolating them from the cytosol.
13
Q
What allow for diffusion of molecules throughout the cell?
A
The cytosol
14
Q
Where is the genetic material encoded in deoxyribonucleic acid (DNA) and how is this DNA organized?
A
In the nucleus, and it is organized into chromosomes. ALL genetic material necessary to replicate the cell is located in the nucleus.
15
Q
How do eukaryotic cells reproduce? And what do they produce when reproducing?
A
Mitosis, and allows the formation of two identical daughter cells.
16
Q
- What is the difference between the cytoplasm and the cytosol?*
A
Cytoplasm includes all structures and organelles within a cell. The cytosol is the fluid within the cell, and everything floats in it!
17
Q
What is the nucleus surrounded by? And what does it maintain?
A
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.
18
Q
What, within the nuclear membrane or envelope, allows for a selective two-way exchange of material between the cytoplasm and the nucleus?
A
The nuclear pores.
19
Q
What are the coding regions of DNA?
A
Genes.
20
Q
What is linear DNA wound around? After being wound, what it is further wound into?
A
Organizing proteins called histones. Linear strands called chromosomes.
21
Q
What does the location of DNA in the nucleus permit in relation to transcription and translation?
A
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.
22
Q
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?
A
Ribosomal RNA (rRNA)
23
Q
What is often called the power plants of the cell, in reference to their important metabolic functions?
A
Mitochondria (plural) Mitochondrion (singular)
24
Q
How many layers does a mitochondrion consist of and what are their purpose?
A
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).
25
What are the numerous infoldings in which the inner membrane of the mitochondrion is arranged?
Why are they arranged this way?
Cristae.
These highly convoluted structures that increase the surface area available for electron transport chain enzymes.
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?
Intermembrane space
Mitochondrial matrix
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.
(No Answer)
28
What establishes the proton-motive force?
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.
29
Why are mitochondria different from other parts of a cell and what do they contain?
They are semi-autonomous. They contain some of their own genes and replicate independently of the nucleus via binary fission.
30
Why are mitochondria considered semi-autonomous?
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.
31
What is a typical or paradigmatic example of cytoplasmic or extranuclear inheritance?
The transmission of genetic matieral independent of the nucleus.
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.
Apoptosis
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?
Lysosomes
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.
Endosomes
35
Why does the lysosomal membrane sequester its enzymes? And what is the process called when the enzymes are released?
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.
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)?
Endoplasmic reticulum
37
What is studded with ribosomes within a cell and what do they permit?
RER. The ribosomes permit the translation of proteins destined for secretion directly into its lumen.
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?
SER. This structure also transports proteins from the RER to the Golgi apparatus.
39
What consists of stacked membrane-bound sacs where materials are transferred to in vesicles?
Golgi apparatus
40
What happens to the materials once inside the golgi apparatus?
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.
41
What happens after the modification and sorting of the products within the GA? What happens if the cellular products are destined for secretion?
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).
42
What cellular component contains hydrogen peroxide, and has a primary function to breakdown very long chain fatty acids via B-oxidation?
Perioxisomes. They also participate in the synthesis of phospholipids and contain some of the enzymes involved in the pentose phosphate pathway.
43
Give 2 examples of cells not having the same distribution of organelles? Form will follow function.
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.
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.
Cytoskeleton.
45
What are the three components of the cytoskeleton?
Microfilaments, microtubules, and intermediate filaments.
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?
Microfilaments
47
Which component of the cytoskeleton can use ATP to generate force for movement by interacting with myosin, such as muscle contraction?
Microfilaments or actin filaments.
48
Which component of the cytoskeleton also plays a role in cytokinesis, or the division of materials between daughter cells during mitosis?
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.
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?
Microtubules
50
What are the motile structures composed of microtubules?
Cilia and flagella
51
What is the difference between cilia and flagella even though they have the same structure?
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.
52
Anatomically, what are cilia and flagella composed of?
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.
53
What can be found in a region of cell called the centrosome?
Centrioles
54
How are centrioles within the centrosomes structured and what is their purpose?
They are the organizing centers for microtubules and are structured as 9 triplets (not pairs) of microtubules with a hollow center.
55
What is the role of the centrioles during mitosis?
They migrate to opposite sides of the dividing cell and organize the mitotic spindle.
56
What do the microtubules emanating from the centrioles accomplish?
They attach to the chromosomes via complexes called kinetochores and exert force on the sister chromatids, pulling them apart.
57
What are a diverse group of filamentous proteins, which includes keratin, desmin, vimentin, and lamins?
Intermediate filaments
58
What are many intermediate filaments involved in?
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.
59
What are the identity of the intermediate filaments proteins within a cell dependent upon?
Specific to the cell and tissue type
60
What do you call the unique characteristic whereas different eukaryotic cells within a tissue may carry out different functions?
Division of labor
61
What are the four types of tissue?
Epithelial tissue, connective tissue, muscles tissue, and nervous tissue.
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.
Epithelial tissue.
63
Other than attaching tightly to each other, what else do epithelial cells attach to?
To underlying connective tissue called the basement membrane.
64
In most organs, epithelial cells constitute as what since these cells can serve many functions depending on the identity of the organ?
Constitute the parenchyma, or the functional parts of the organ.
65
What are examples of the parenchyma for the kidneys, liver, and stomach?
The nephrons in the kidney are composed of epithelial cells, hepatocytes in the liver, and acid-producing cells of the stomach.
66
How are the different epithelia LAYERS classified?
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.
67
How are the different epithelia SHAPES classified?
Cubodial cells are cube-shaped.
Columnar cells are long and thing.
Squamous cells are flat and scale like.
68
What supports the body and provides a framework for the epithelial cells to carry out their function?
Connective tissue.
69
Whereas epithelial cells contribute to the parenchyma of an organ, connective tissues are the main contributors to the _ _ _ _ _ or support structure.
Stroma
70
What are examples of connective tissue?
Bone, cartilage, tendons, ligaments, adipose tissue, and blood are all examples of connective tissue.
71
Why do most cells in connective tissues produce and secrete materials such as collagen and elastin?
The extracellular matrix (the areas between the cells)
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?
Nucleoid region.
73
What are the three domains in which all life is classfied?
Archaea, Bacteria, and Eukarya.
Archaea and bacteria contain prokaryotes.
74
T/F Archaea, single-celled organisms, are visually more similar to Eukarya than Bacteria.
False. Archaea are visually more similar to bacteria, but contain genes and several metabolic pathways that are more similar to eukaryotes.
75
What is a word for Archaea that can withstand harsh environments with extremely high temperatures, high salinity, or no light?
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.
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.
No Answer
77
Name all the structures that all bacteria have (3)
1. cell membrane
2. cytoplasm
3. flagella or fimbriae (similar to cilia)
78
What type of relationship exists where both organisms benefit?
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.
79
What does parasite or pathogen mean?
It means they provide no advantage or benefit to the host, but rather cause disease.
80
What does it mean that pathogenic bacteria can live intracellularly and extracellularly?
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.
81
What is classification of bacteria by shape so important?
It helps scientists and pathologists a common language to talk about bacteria, as well as to identify different species of bacteria.
82
What are the three shapes that most bacteria exist?
Cocci - spherical bacteria like Streptococcus pyogenes
Bacilli - rod-shaped bacteria like Escherichia coli
Spirilli - spiral-shaped bacteria like Treponema pallidum
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.
No Answer
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
No Answer
85
What do you call bacteria that require oxygen for metabolism?
Obligate aerobes
86
What do you call bacteria that use fermentation, or some other form of cellular metabolism that does not require oxygen?
Anaerobes
87
What do you call anaerobes that cannot survive in an oxygen-containing environment?
Obligate anaerobes.
The presence of oxygen leads to the production of reactive-oxygen containing radicals in this species, which leads to cell death.
88
What are facultative anaerobes?
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.
89
What are bacteria that are unable to use oxygen for metabolism, but are not harmed by its presence in the environment?
Aerotolerant anaerobes
90
What are some of the main differences between prokaryotes and eukaryotes?
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.
91
What is the outer and inner wall of a bacterium or prokaryote?
Cell wall is the outer layer, and the cell (or plasma) membrane, which is composed of phospholipids, is the inner wall.
92
What does the cell wall and the cell membrane make up?
The envelope of the cell.
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?
The cell wall of the organism
94
What are the two types of cell walls?
Gram positive and gram negative.
95
How is the type of cell wall determined?
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.
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?
Gram-positive cell wall.
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.
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.
98
Real World: What does the antibiotic penicillin target within gram-positive bacteria like streptococcus (strep throat) and treponema (syphilis)?
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.
99
What is the ability of a cell to detect chemical stimuli and move toward or away from them is called?
Chemotaxis
100
What is a flagellum composed of?
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.
101
What is a hollow, helical structure composed of flagellin?
A filament
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?
The basal body
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?
The hook.
104
What is DNA acquired from external sources may also be carried on smaller circular structures known as?
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.
105
True/False Prokaryotes lack several key organelles, such as mitochondria.
True
106
How do prokaryotes generate ATP?
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.
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?
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.
108
What is the extrachromosomal (extragenomic) material found within bacteria?
Plasmids
These typically carry genes that impart some benefit to the bacterium, such as antibiotic resistance, antibiotic degrading enzyme or altering enzyme, etc.
109
Plasmids may carry additional virulence factors, what does this mean?
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.
110
What is a subset of plasmids that are capable of integrating into the genome of the bacterium?
Episomes
111
What does bacterial genetic recombination help?
It helps to increase bacterial diversity and thus permits evolution of a bacterial species over time.
112
What are the three recombination processes among bacteria?
Transformation, conjugation, and transduction.
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?
Transformation.
Many gram-negative rods are able to carry our this process.
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?
Conjugation and the conjugation bridge.
The bridge is made from appendages called sex pili that are found on the donor male (+).
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?
It is unidirectional meaning one direction, and the donor male (+) to the recipient female (-).
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?
Sex factors.
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?
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.
118
What does it mean to say cells have undergone a change referred to the abbreviation Hfr (High frequency of recombination)?
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.
119
What is the only genetic recombination process that requires a vector--a virus that carries genetic material from one bacterium to another?
Transduction.
Remember: viruses are obligate intracellular pathogens, which means that they cannot reproduce outside of a host cell.
120
What are viruses that infect bacteria and can accidentally incorporate a segment of host DNA during assembly?
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.
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?
Transposons.
If a transposon is inserted within a coding region of a gene, that gene may be disrupted.
122
In bacterial reproduction, what are the 4 phases of growth?
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
123
What phase within reproduction of bacteria does the resources begin to fall dramatically?
The exponential phase
124
What are viruses composed of?
Genetic material, a protein coat, and sometimes an envelope containing lipids.
125
How is the genetic material in viruses physically shaped and what are they composed of?
Circular or linear, single- or double-stranded, and composed of either DNA or RNA.
126
What is the protein coat known as, which may be surrounded by an envelope composed of phospholipids and virus-specific proteins?
A capsid
127
T/F Enveloped viruses are easier to kill.
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.
128
Why are viruses considered obligate intracellular parasites?
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.
129
What are the replicated and produced viral progeny called when a virus hijacks the host cells machinery?
Virions. These can be released to infect additional cells.
130
What are viruses that specfically target bacteria?
Bacteriophages
They do not actually enter the bacteria; rather, they simply inject their genetic material, leaving the remaining structures outside the infected cell.
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
The tail sheath and tail fibers.
132
What is the difference between a positive sense single strand RNA virus and a negative sense single strand RNA virus?
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.
133
What must Negative-sense RNA viruses carry in the virion to ensure that the complementary strand is synthesized?
RNA replicase
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?
Retroviruses
135
What does reverse transcriptase allow a retrovirus to accomplish?
Allows synthesis of DNA from single-stranded RNA
136
Why are retroviruses so dangerous?
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.
137
What is a very popularized retrovirus?
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.
138
T/F Viruses can infect any type of cells.
False. They can infect cells with certain surface receptors. Without specfic receptors, the cells are invisible to the virus.
139
What are the two ways viruses infect cells?
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.
140
What do most DNA viruses need to happen in order to be transcribed into mRNA?
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.
141
What are most of the proteins created by virions once hyjacking is complete?
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.
142
What are the two general ideas of viral progeny release? (3)
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
143
Why is lysis of a host cell a disadvantage to a virion?
The virus can no longer use the cell to carry out its life cycle.
144
What is known as extrusion?
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.
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.
It depends on growth conditions and the specific virus.
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?
Lytic cycle.
Once the host is swollen with new virions, the cell lyses, and other bacteria can be infected.
147
What are viruses in the lytic phase termed as?
Virulent
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?
Lysogenic cycle
The virus is now replicated because it is now a part of the host's genome.
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?
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.
150
Why might it be an advantage if a phage integrates with a host genome even though it could kill it?
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.
151
What are, generally, prions and viroids?
Very small (subviral) particles that can cause disease under certain circunstances.
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?
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.
153
What are small pathogens consisting of a very short circular single-stranded RNA that infect plants?
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.
