4: Cell Structure Flashcards
Studying Cells, Prokaryotic Cells, Eukaryotic Cells, the Endomembrane System and Proteins, the Cytoskeleton, Connections between Cells and Cellular Activities
1
Q
What is (unified) cell theory?
A
A biological concept that states that all organisms are composed of one or more cells; the cell is the basic unit of life; and new cells arise from existing cells.
2
Q
What is a microscope?
A
An instrument that magnifies an object.
3
Q
What is an electron microscope?
A
An instrument that magnifies an object using a beam of electrons passed and bent through a lens system to visualize a specimen.
4
Q
What is a light microscope?
A
An instrument that magnifies an object using a beam of visible light passed and bent through a lens system to visualize a specimen.
5
Q
What is a cell?
A
A cell is the smallest unit of a living thing (an organism), which can be made of one cell or many cells. Cells are the basic building blocks of all organisms.
6
Q
What are the levels of organization of an organism?
A
Cells of one kind that interconnect with each other and perform a shared function form tissues, tissues combine to form an organ, organs combine to form an organ system, and organ systems together form an organism.
7
Q
What are the broad categories of cells?
A
Prokaryotic and eukaryotic.
8
Q
What are some examples of prokaryotic and eukaryotic cells?
A
Animal and plant cells are eukaryotic and bacterial cells are prokaryotic.
9
Q
What are micrographs?
A
Photographs of cells taken with a microscope.
10
Q
How does a microscope lens change the orientation of an image?
A
A specimen that is right-side up and facing right on the microscope slide will appear upside-down and facing left when view through a microscope. If the slide is moved left, it will appear to move right, and if moved down will appear to move up.
11
Q
Why are microscope images inverted?
A
Because microscopes use two sets of lenses to magnify the image. Because of the manner in which light travels through the lenses, this system of two lenses produces an inverted image.
12
Q
What are binocular or dissecting microscopes?
A
These microscopes include an additional magnification system that makes the final image appear upright.
13
Q
How large are typical human red blood cells?
A
They are about eight millionths of a meter or eight micrometers (8 μm) in diameter. About 250 red blood cells could fit on the head of a pin, which is about two thousandths of a meter (2 mm).
14
Q
What are the downsides of viewing cells with light microscopes?
A
Individual cells are generally transparent, and their components are not distinguishable unless they are colored with special stains, which usually kills the cells.
15
Q
Which parameters are important in microscopy?
A
Magnification and resolving power.
16
Q
What is magnification?
A
Magnification is the process of enlarging an object in appearance.
17
Q
What is resolving power?
A
Resolving power is the ability of a microscope to distinguish two adjacent structures as separate: the higher the resolution, the better the clarity and detail of the image.
18
Q
What do oil immersion lenses do?
A
They can usually increase magnification up to 1000 times.
19
Q
Which category of microscope is used to study cellular structure and function?
A
Electron microscopes.
20
Q
What is the magnification and resolution of a typical light microscope used in a college biology lab?
A
The magnification is approximately 400 times with a resolution of about 200 nanometers.
21
Q
What is the magnification and resolution of a typical electron microscope?
A
The magnification is approximately 100,000 times with a resolution of about 50 picometers.
22
Q
What is the impact of electron microscopy on a specimen?
A
The method used to prepare the specimen for viewing with an electron microscope kills the organism. Electrons have short wavelengths (shorter than photons) that move best in a vacuum, so living cells cannot be viewed with an electron microscope.
23
Q
How do scanning electron microscopes work?
A
A beam of electrons moves back and forth across a cell’s surface, creating details of cell surface characteristics.
24
Q
How do transmission electron microscopes work?
A
An electron beam penetrates the cell and provides details of a cell’s internal structures.
25
Who was Antony van Leeuwenhoek?
A Dutch shopkeeper with great skill in crafting lenses in the 1600s and who was able to observe the movements of protists and sperm, which he collectively termed “animalcules”.
26
When was the term “cell” first used in publication?
In a 1665 publication called *Micrographia*, experimental scientist Robert Hooke coined the term “cell” for the box-like structures he observed when viewing cork tissue through a lens.
27
When were bacteria and protozoa discovered?
In the 1670s by Antony van Leeuwenhoek.
28
When was the unified cell theory proposed?
In the late 1830s, botanist Matthias Schleiden and zoologist Theodor Schwann were studying tissues and proposed the unified cell theory. Rudolf Virchow later made important contributions to the theory.
29
What is a pap smear?
A test in which a doctor takes a small sample of cells from the uterine cervix of a patient and sends it to a medical lab where a cytotechnologist stains the cells and examines them for any changes that could indicate cervical cancer or a microbial infection.
30
What do cytotechnologists do?
Cytotechnologists are professionals who study cells via microscopic examinations and other laboratory tests. They are trained to determine which cellular changes are within normal limits and which are abnormal. They study cellular specimens that come from all organs. When they notice abnormalities, they consult a pathologist, who is a medical doctor who can make a clinical diagnosis.
31
What is a nucleoid?
The central part of a prokaryotic cell in which the chromosome is found.
32
What is a prokaryote?
A unicellular organism that lacks a nucleus or any other membrane-bound organelle.
33
What are the common components of all cells?
1. Plasma membrane
2. Cytoplasm
3. DNA
4. Ribosomes
34
What is the purpose of a prokaryotic cell wall?
Most prokaryotes have a peptidoglycan cell wall that acts as an extra layer of protection, helps the cell maintain its shape, and prevents dehydration.
35
What is the purpose of a prokaryotic capsule?
Most prokaryotes have a polysaccharide capsule that enables the cell to attach to surfaces in its environment.
36
What is the purpose of prokaryotic flagella?
Some prokaryotes have flagella which are used for locomotion.
37
What is the purpose of pili?
Some prokaryotes have pili which are used to exchange genetic material during a type of reproduction called conjugation.
38
What is the purpose of fimbriae?
Some prokaryotes have fimbriae that are used by bacteria to attach to a host cell.
39
What are some examples of beneficial microbes?
Microbes in the gut that make vitamin K and those that ferment beer and wine.
40
What are some industries in which microbiologists work?
The food industry, veterinary and medical fields, and in the pharmaceutical sector, serving key roles in research and development by identifying new sources of antibiotics that could be used to treat bacterial infections.
41
How do microbiologists work in bioremediation?
Environmental microbiologists may look for new ways to use specially selected or genetically engineered microbes for the removal of pollutants from soil or groundwater, as well as hazardous elements from contaminated sites.
42
How do microbiologists work in bioinformatics?
They provide specialized knowledge and insight for the design, development, and specificity of computer models, for example of bacterial epidemics.
43
How large are cells?
Prokaryotic cells are on average between 0.1 and 5.0 μm in diameter, while eukaryotic cells have diameters ranging from 10 to 100 μm.
44
What are some benefits of the small size of prokaryotes?
The small size of prokaryotes allows quick entry and diffusion of ions and molecules to other parts of the cell while also allowing fast removal of waste products out of the cell.
45
Why is the size of cells limited?
The formula for the surface area of a sphere is 4π2, while the formula for its volume is 4π2/3. Thus, as the radius of a cell increases, its surface area increases as the square of its radius, but its volume increases as the cube of its radius (much more rapidly). Therefore, as a cell increases in size, its surface area-to-volume ratio decreases. If the cell grows too large, the plasma membrane will not have sufficient surface area to support the rate of diffusion required for the increased volume. In other words, as a cell grows, it becomes less efficient.
46
What are some ways in which cells can become more efficient when growing in size?
Cell division, or the evolutionary development of organelles to perform specific tasks.
47
What is a cell wall?
A rigid cell covering that protects the cell, provides structural support, and gives shape to the cell.
48
What is a central vacuole?
A large plant cell organelle that regulates the cell's storage compartment, holds water, and plays a significant role in cell growth as the site of macromolecule degradation.
49
What is a centrosome?
A region in animal cells made of two centrioles.
50
What is chlorophyll?
A green pigment that captures the light energy that drives the light reactions of photosynthesis.
51
What is a chloroplast?
A plant cell organelle that carries out photosynthesis.
52
What is chromatin?
A protein-DNA complex that serves as the building material of chromosomes.
53
What is a chromosome?
A structure within the nucleus or nucleoid that is made up of chromatin that contains DNA, the hereditary material.
54
What is cytoplasm?
The entire region between the plasma membrane and the nuclear envelope, consisting of organelles suspended in the gel-like cytosol, the cytoskeleton, and various chemicals.
55
What is cytosol?
The gel-like material of the cytoplasm in which cell structures are suspended.
56
What is a eukaryotic cell?
A cell that has a membrane-bound nucleus and several other membrane-bound compartments or sacs.
57
What is a lysosome?
An organelle in an animal cell that functions as the cell's digestive component; it breaks down proteins, polysaccharides, lipids, nucleic acids, and even worn-out organelles.
58
What are mitochondria?
Cellular organelles responsible for carrying out cellular respiration, resulting in the production of ATP, the cell's main energy-carrying molecule. Singular = mitochondrion.
59
What is a nuclear envelope?
A double-membrane structure that constitutes the outermost portion of the nucleus.
60
What is a nucleolus?
A darkly staining body within the nucleus that is responsible for assembling the subunits of the ribosomes.
61
What is nucleoplasm?
Semi-solid fluid inside the nucleus that contains the chromatin and nucleolus.
62
What is a nucleus?
A cell organelle that houses the cell's DNA and directs the synthesis of ribosomes and proteins.
63
What is an organelle?
A compartment or sac within a cell.
64
What is a peroxisome?
A small, round organelle that contains hydrogen peroxide, oxidizes fatty acids and amino acids, and detoxifies many poisons.
65
What is a plasma membrane?
Phospholipid bilayer with embedded (integral) or attached (peripheral) proteins, and separates the internal content of the cell from its surrounding environment.
66
What is a ribosome?
A cellular structure that carries out protein synthesis.
67
What is a vacuole?
A membrane-bound sac, somewhat larger than a vesicle, which functions in cellular storage and transport.
68
What is a vesicle?
Small, membrane-bound sac that functions in cellular storage and transport; its membrane is capable of fusing with the plasma membrane and the membranes of the endoplasmic reticulum and Golgi apparatus.
69
What differences are there in eukaryotic cells from prokaryotic cells?
Eukaryotic cells have a membrane-bound nucleus, membrane-bound organelles such as the endoplasmic reticulum, Golgi apparatus, chloroplasts, and mitochondria, and rod-shaped chromosomes.
70
What is a phospholipid?
A lipid molecule with two fatty acid chains and a phosphate-containing group.
71
How does the plasma membrane regulate cell behavior?
The plasma membrane controls the passage of organic molecules, ions, water, and oxygen into and out of the cell. Wastes (such as carbon dioxide and ammonia) also leave the cell by passing through the plasma membrane.
72
What are microvilli?
The plasma membranes of cells that specialize in absorption are folded into fingerlike projections called microvilli (singular = microvillus).
73
Where are cells with microvilli found?
They are typically found lining the small intestine, the organ that absorbs nutrients from digested food.
74
What is the cause and effect of celiac disease?
People with celiac disease have an immune response to gluten, which is a protein found in wheat, barley, and rye. The immune response damages microvilli, and thus, afflicted individuals cannot absorb nutrients. This leads to malnutrition, cramping, and diarrhea. Patients suffering from celiac disease must follow a gluten-free diet.
75
What is the cytoplasm composed of?
The cytoplasm is 70 to 80% water but has a semi-solid consistency from the proteins within it. Glucose and other simple sugars, polysaccharides, amino acids, nucleic acids, fatty acids, and derivatives of glycerol are also found in the cytoplasm. Ions of sodium, potassium, calcium, and many other elements are dissolved in the cytoplasm. Many metabolic reactions, including protein synthesis, take place here.
76
How can the nuclear envelope be crossed?
The nuclear envelope is punctuated with pores that control the passage of ions, molecules, and RNA between the nucleoplasm and the cytoplasm.
77
What is the shape of chromosomes?
In prokaryotes, DNA is organized into a single circular chromosome. In eukaryotes, chromosomes are linear structures. Every eukaryotic species has a specific number of chromosomes in the nuclei of its body's cells.
78
How many chromosomes do humans have?
46
79
How many chromosomes do fruit flies have?
8
80
When are chromosomes visible?
Chromosomes are only visible and distinguishable from one another when the cell is getting ready to divide. When the cell is in growth and maintenance phases of its life cycle, proteins are attached to chromosomes, and they resemble an unwound, jumbled bunch of threads.
81
Where are ribosomes found?
They appear either as clusters (polyribosomes) or single, tiny dots that float freely in the cytoplasm, or they may be attached to the cytoplasmic side of the plasma membrane or the cytoplasmic side of the endoplasmic reticulum and the outer membrane of the nuclear envelope.
82
What are the subunits of ribosomes?
The large subunit and the small subunit.
83
What is the role of ribosomes?
Ribosomes receive their “orders” for protein synthesis from the nucleus where the DNA is transcribed into mRNA. The mRNA travels to the ribosomes, which translate the code provided by the sequence of the nitrogenous bases in the mRNA into a specific order of amino acids in a protein.
84
In which types of cells are ribosomes found?
Because protein synthesis is an essential function of all cells, ribosomes are found in practically every cell, though they are particularly abundant in cells that synthesize large amounts of protein.
85
What is an example of a cell that contains many ribosomes?
The cells in the pancreas that are responsible for creating digestive enzymes.
86
What is adenosine triphosphate (ATP)?
The cell's main energy-carrying molecule, which represents the short-term stored energy of the cell.
87
What is cellular respiration?
Cellular respiration is the process of making ATP using the chemical energy found in glucose and other nutrients. In mitochondria, this process uses oxygen and produces carbon dioxide as a waste product.
88
Which types of cells have a high concentration of mitochondria?
Muscle cells have a very high concentration of mitochondria. When muscle cells don't get enough oxygen, they produce a smaller amount of ATP, and a larger amount of lactic acid.
89
How are mitochondria structured?
Mitochondria are oval-shaped, double membrane organelles that have their own ribosomes and DNA. Each membrane is a phospholipid bilayer embedded with proteins. The inner layer has folds called cristae, which increase its surface area. The space between the two membranes is called the intermembrane space, and the area surrounded by the folds is called the mitochondrial matrix. The cristae and the matrix have different roles in cellular respiration, and ATP synthesis takes place on the inner membrane.
90
What are the products of peroxisome activity?
Many of the oxidation reactions in peroxisomes release hydrogen peroxide, H2O2, which would be damaging to cells, however when these reactions are confined to peroxisomes, enzymes safely break down the H2O2 into oxygen and water.
91
What are some examples of peroxisomes?
Alcohol is detoxified by peroxisomes in liver cells, and glyoxysomes, which are special peroxisomes in plants, are responsible for converting stored fats into sugars.
92
What are some differences between vesicles and vacuoles?
Vacuoles are somewhat larger than vesicles, however the membranes of vesicles can fuse with either the plasma membrane or other membranes within the cell. Additionally, some agents such as enzymes within plant vacuoles break down macromolecules. The membrane of a vacuole does not fuse with the membranes of other cellular components.
93
What are some differences between animal and plant cells?
While both animal and plant cells have microtubule organizing centers (MTOCs), animal cells also have centrioles associated with the MTOC: a complex called the centrosome. Animal cells each have a centrosome and lysosomes, whereas plant cells do not. Plant cells have a cell wall, chloroplasts and other specialized plastids, and a large central vacuole, whereas animal cells do not.
94
How is a centrosome structured?
The centrosome is a microtubule-organizing center found near the nuclei of animal cells. It contains a pair of centrioles, two structures that lie perpendicular to each other. Each centriole is a cylinder of nine triplets of microtubules. Non-tubulin proteins hold the microtubule triplets together.
95
What is the role of centrioles in cell division?
Centrioles seem to have some role in pulling duplicated chromosomes to oppose ends of the dividing cell. The exact function in cell division is not clear, because cells that have had the centrosome removed can still divide; and plant cells, which lack centrosomes are capable of cell division.
96
What is the pH within lysosomes?
The pH within lysosomes is more acidic than that of the cytoplasm, and their enzymes are active at a much lower pH than those in the cytoplasm.
97
What is the role of a cell wall?
The cell wall is a rigid covering that protects the cell, provides structural support, and gives shape to the cell.
98
What are some organisms that have cell walls?
Plants, fungi, and protists have cell walls.
99
What is the main component of cell walls?
The chief component of prokaryotic cell walls is peptidoglycan, and the major organic molecule in plant cell walls is cellulose, a polysaccharide made up of glucose monomers.
100
What is cellulose?
A long chain of beta-glucose molecules connected by 1-4 linkages.
101
What is photosynthesis?
Photosynthesis is the series of reactions that use carbon dioxide, water, and light energy to make glucose and oxygen.
102
What is the major difference between plants and animals?
Plants are autotrophs and are able to make their own food, like sugars, while animals are heterotrophs and must ingest their food.
103
How are chloroplasts structured?
Like mitochondria, chloroplasts have their own DNA (as a single circular chromosome) and ribosomes, and they have outer and inner membranes. Within the space enclosed by a chloroplast's inner membrane is a set of interconnected and stacked fluid-filled membrane sacs called thylakoids. The space inside the thylakoid membranes is called the thylakoid space. Each stack of thylakoids is called a granum (plural = grana). The fluid enclosed by the inner membrane that surrounds the grana is called the stroma.
104
Where does the main activity take place in a chloroplast?
The light harvesting reactions take place in the thylakoid membranes, and the synthesis of sugar takes place in the stroma.
105
Where is chlorophyll found in photosynthetic protists and bacteria?
Photosynthetic protists have chloroplasts like plant cells, but chlorophyll in photosynthetic bacteria is not relegated to an organelle.
106
What is symbiosis?
Symbiosis is a relationship in which organisms from two separate species depend on each other for their survival.
107
What is endosymbiosis?
Endosymbiosis is a mutually beneficial relationship in which one organism lives inside another.
108
What is an example of endosymbiosis in humans?
The microbes that live inside the human gut that produce vitamin K. It is beneficial for us because we are unable to synthesize vitamin K, and it is beneficial for the microbes because they are protected from other organisms and from drying out, and they receive abundant food from the environment of the large intestine.
109
What is the endosymbiosis hypothesis of mitochondria and chloroplasts?
Scientists believe that host cells and bacteria formed an endosymbiotic relationship when the host cells ingested both aerobic and autotrophic bacteria (cyanobacteria) but did not destroy them. Through millions of years of evolution, these ingested bacteria became more specialized in their functions, with the aerobic bacteria becoming mitochondria and the autotrophic bacteria becoming chloroplasts.
110
What causes the wilting of plants?
The wilting of plants is caused by the loss of water from the vacuole, which reduces support for the cell wall.
111
How does the central vacuole support cell expansion?
When the central vacuole holds more water, the cell gets larger without having to invest a lot of energy in synthesizing new cytoplasm.
112
What is the endomembrane system?
The group of organelles and membranes in eukaryotic cells that work together modifying, packaging, and transporting lipids and proteins.
113
What is the endoplasmic reticulum (ER)?
A series of interconnected membranous structures within eukaryotic cells that collectively modify proteins and synthesize lipids.
114
What is the Golgi apparatus?
A eukaryotic organelle made up of a series of stacked membranes that sorts, tags, and packages lipids and proteins for distribution.
115
What is the rough endoplasmic reticulum (RER)?
The region of the endoplasmic reticulum that is studded with ribosomes and engages in protein modification and phospholipid synthesis.
116
What is the smooth endoplasmic reticulum (SER)?
A region of the endoplasmic reticulum that has few or no ribosomes on its cytoplasmic surface and synthesizes carbohydrates, lipids, and steroid hormones; detoxifies certain chemicals, and stores calcium ions.
117
What is included in the endomembrane system?
The endomembrane system includes the nuclear envelope, lysosomes, vesicles, the endoplasmic reticulum, Golgi apparatus, and the plasma membrane (even though not technically *within* the cell). It does not include the membranes of either mitochondria or chloroplasts.
118
What is the lifecycle of an integral membrane protein before it becomes embedded in the cell membrane?
Membrane and secretory proteins are synthesized in the rough endoplasmic reticulum (RER). The RER also sometimes modifies the protein. A vesicle with the protein buds from the ER and fuses with the cis face of the Golgi apparatus. As the protein passes along the Golgi's cisternae, it is further modified by the addition of more carbohydrates. After its synthesis is complete, it exits in a vesicle that buds from the Golgi's trans face and when the vesicle fuses with the cell membrane, the protein becomes an integral portion of the membrane.
119
What is the hollow portion of ER tubules called?
The lumen or cisternal space.
120
Where is the ER found relative to the nucleus?
The membrane of the ER is continuous with the nuclear envelope.
121
What is the role of the RER?
Ribosomes transfer newly synthesized proteins into the lumen or the RER where they undergo structural modifications, such as folding or the acquisition of side chains. These modified proteins will be incorporated into cellular membranes—the membrane of the ER or those of other organelles—or secreted from the cell (such as protein hormones, enzymes). The RER also makes phospholipids for cellular membranes.
122
How do proteins and phospholipids reach their target destinations from the RER?
If they are not destined to stay in the RER, they will reach their destinations via transport vesicles that bud from the RER's membrane.
123
In which cell types is the RER most abundant?
The RER is especially prominent in cells that secrete proteins, such as liver cells.
124
What is the sarcoplasmic reticulum?
In muscle cells, a specialized SER that is responsible for storage of the calcium ions that are needed to trigger the coordinated contractions of the muscle cells.
125
What is heart failure?
Heart failure is just one of many disabling heart conditions. Heart failure does not mean that the heart has stopped working, but rather that it cannot pump with sufficient force to transport oxygenated blood to all the vital organs. Left untreated, heart failure can lead to kidney failure and failure of other organs.
126
What causes heart failure?
The wall of the heart is composed of cardiac muscle tissue. Heart failure occurs when the endoplasmic reticula of cardiac muscle cells do not function properly. As a result, an insufficient number of calcium ions are available to trigger a sufficient contractile force.
127
What do cardiologists do?
Cardiologists are doctors who specialize in treating heart diseases, including heart failure. Cardiologists can make a diagnosis of heart failure via physical examination, results from an electrocardiogram (ECG, a test that measures the electrical activity of the heart), a chest X-ray to see whether the heart is enlarged, and other tests. If heart failure is diagnosed, the cardiologist will typically prescribe appropriate medications and recommend a reduction in table salt intake and a supervised exercise program.
128
How is the Golgi apparatus structured?
The Golgi apparatus is a series of flattened membranes. The receiving side is called the *cis* face, and the opposite side is called the *trans* face.
129
What occurs to proteins and lipids in the lumen of the Golgi apparatus?
As the proteins and lipids travel through the Golgi, they undergo modifications that allow them to be sorted. The most frequent modification is the addition of short chains of sugar molecules. These newly modified proteins and lipids are then tagged with phosphate groups or other small molecules so that they can be routed to their proper destinations.
130
What happens to proteins and lipids when they are finished in the Golgi?
The modified and tagged proteins are packaged into secretory vesicles that bud from the trans face of the Golgi. Some of these vesicles deposit their contents into other parts of the cell where they will be used, or they may fuse with the plasma membrane and release their contents outside the cell.
131
In which types of cells is Golgi most abundant?
Golgi is abundant in cells which engage in a lot of secretory activity, such as salivary glands that secrete digestive enzymes or cells of the immune system that secrete antibodies.
132
What are some other responsibilities of the Golgi apparatus in plant cells?
In plant cells, the Golgi apparatus also synthesizes polysaccharides which are incorporated into the cell wall or used in other parts of the cell.
133
What is Lowe disease?
AKA oculocerebrorenal syndrome, because it affects the eyes, brain, and kidneys, there is a deficiency in an enzyme localized to the Golgi apparatus. Children with Lowe disease are born with cataracts, typically develop kidney disease after the first year of life, and may have impaired mental abilities.
134
How does genetics cause Lowe disease?
Lowe disease is a genetic disease caused by a mutation on the X chromosome. The X chromosome is one of the two human sex chromosomes, which determine a person's sex. Females possess two X chromosomes while males possess one X and one Y. In females, the genes on only one of the two X chromosomes are expressed. Therefore, females who carry the Lowe disease gene on one of their X chromosomes have a 50/50 chance of having the disease. However, males who carry the gene have a 100% chance of having the disease. The location of the mutated gene has been identified by scientists and can be identified in fetuses through prenatal testing of pregnant women.
135
What do geneticists do?
Geneticists analyze the result of prenatal genetic tests and may counsel pregnant women on their options. They may conduct genetic research that leads to new drugs or foods, or perform DNA analyses that are used in forensic investigations.
136
How do lysosomes destroy pathogens?
Lysosomes use their hydrolytic enzymes to destroy pathogens that might enter a cell. In a process known as phagocytosis or endocytosis, a section of the plasma membrane invaginates (folds in) and engulfs a pathogen. The invaginated section with the pathogen inside pinches off from the plasma membrane and becomes a vesicle. The vesicle fuses with a lysosome, and the lysosome's hydrolytic enzymes then destroy the pathogen.
137
What is a cilium?
A short, hair-like structure that extends from the plasma membrane in larger numbers and is used to move an entire cell or move substances along the outer surface of the cell. Plural = cilia.
138
What is the cytoskeleton?
The network of protein fibers that collectively maintain the shape of the cell, secure some organelles in specific positions, allow cytoplasm and vesicles to move within the cell, and enable unicellular organisms to move independently.
139
What is a flagellum?
A long, hair-like structure that extends from the plasma membrane and is used to move the cell. Plural = flagella.
140
What is an intermediate filament?
A cytoskeletal component, composed of several intertwined strands of fibrous protein, that bears tension, supports cell-cell junctions, and anchors cells to extracellular structures.
141
What is a microfilament?
The narrowest element of the cytoskeleton system; it provides rigidity and shape to the cell and enables cellular movements.
142
What is a microtubule?
The widest element of the cytoskeleton system; it helps the cell resist compression, provides a track along which vesicles move through the cell, pulls replicated chromosomes to opposite ends of a dividing cell, and is the structural element of centrioles, flagella, and cilia.
143
What are the types of fibers within the cytoskeleton?
Microfilaments, intermediate filaments, and microtubules.
144
How are microfilaments structured?
They have a diameter of about 7 nm and are made of two intertwined strands of a globular protein called actin, and so are also known as actin filaments.
145
How does actin enable microfilament activity?
Actin is powered by ATP to assemble its filamentous form, which serves as a track for the movement of a motor protein called myosin. This enables actin to engage in cellular events requiring motion, such as cell division in animal cells and cytoplasmic streaming, which is the circular movement of the cell cytoplasm in plant cells. Actin and myosin are plentiful in muscle cells. When actin and myosin filaments slide past each other, muscles contract.
146
How do microfilaments allow a cell to change shape?
Microfilaments provide some rigidity and shape to the cell. They can depolymerize and reform quickly, enabling a cell to change its shape and move.
147
What is an example of a cell that uses microfilaments to move quickly?
White blood cells move to the site of an infection and phagocytize the pathogen.
148
How large are intermediate filaments?
Their diameter is between 8 and 10 nm, which is in between microfilaments and microtubules.
149
What is the role of intermediate filaments?
They have no role in cell movement, and their function is purely structural. They bear tension, thus maintaining the shape of the cell, and anchor the nucleus and other organelles in place.
150
What are intermediate filaments made of?
They are the most diverse group of cytoskeletal elements, made up of several types of fibrous proteins such as keratin.
151
Where is keratin found?
Keratin is a fibrous protein that strengthens human hair, nails, and the epidermis of the skin.
152
What are microtubules made of?
The walls of microtubules are made of polymerized dimers of alpha-tubulin and beta-tubulin, two globular proteins. They have a diameter of about 25 nm and like microfilaments can dissolve and reform quickly.
153
What are some examples of cilia?
The cilia of paramecia move the entire cell, while the cilia of the cells lining the Fallopian tubes move the ovum toward the uterus, and the cilia lining the cells of the respiratory tract trap particulate matter and move it toward the nostrils.
154
In what ways are flagella and cilia similar?
Flagella and cilia share a common structural arrangement of microtubules called a “9 + 2 array”, meaning they are made of a ring of nine microtubule doublets, surrounding a single microtubule doublet in the center.
155
What is a desmosome?
A linkage between adjacent cells that form when cadherins in the plasma membrane attach to intermediate filaments.
156
What is the extracellular matrix?
Material (primarily collagen, glycoproteins, and proteoglycans) secreted from animal cells that provides mechanical protection and anchoring for the cells in the tissue.
157
What is a gap junction?
A channel between two adjacent animal cells that allows ions, nutrients, and low molecular weight substances to pass between cells, enabling the cells to communicate.
158
What is a plasmodesma?
A channel that passes between the call wells of adjacent plant cells, connects their cytoplasm, and allows materials to be transported from cell to cell. Plural = plasmodesmata.
159
What is a tight junction?
A firm seal between two adjacent animal cells created by protein adherence.
160
How does the extracellular matrix facilitate to cell communication?
Cells have protein receptors on the extracellular surfaces of their plasma membranes. When a molecule within the matrix binds to the receptor, it changes the molecular structure of the receptor. The receptor, in turn, changes the conformation of the microfilaments positioned just inside the plasma membrane. These conformational changes induce chemical signals inside the cell that reach the nucleus and turn “on” or “off” the transcription of specific sections of DNA, which affects the production of associated proteins, changing the activities within the cell.
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How does the extracellular matrix stimulate blood clotting?
When the cells lining a blood vessel are damaged, they display a protein receptor called a tissue factor. When the tissue factor binds with another factor in the extracellular matrix, it causes platelets to adhere to the wall of the damaged blood vessel, stimulates the adjacent smooth muscle cells in the blood vessel to contract (constricting the blood vessel), and initiates a series of steps that stimulate the platelets to produce clotting factors.
162
What are intercellular junctions?
Cells in adjacent contact that can communicate with each other directly.
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What are some types of intercellular junctions?
Plasmodesmata are junctions between plant cells, whereas tight junctions, gap junctions, and desmosomes are found in animal cells.
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Which proteins are predominant in forming tight junctions?
Claudins and occludins.
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Where are tight junctions found?
The tight adherence prevents materials from leaking between the cells, so tight junctions are typically found in epithelial tissues that line internal organs and cavities, and comprise most of the skin. For example, tight junctions of the epithelial cells lining urinary bladders prevent urine from leaking out into the extracellular space.
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What do cadherins do?
The cadherins in desmosomes join two adjacent cells together and maintain the cells in a sheet-like formation in organs and tissues that stretch, like the skin, heart, and muscle.
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How do gap junctions form?
Gap junctions develop when a set of six proteins (called connexins) in the plasma membrane arrange themselves in an elongated donut-like configuration called a connexon. When the pores ("donut holes") of connexons in adjacent animal cells align, a channel between the two cells forms.
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In which cell types are gap junctions particularly important?
Gap junctions are particularly important in cardiac muscle. The electrical signal for the muscle to contract is passed efficiently through gap junctions, allowing the heart muscle cells to contract in tandem.
