CH.3 : THE CELLULAR LEVEL OF ORGANIZATION Flashcards
1
Q
What are cells?
A
any living structural and functional units enclosed by a membrane
2
Q
What is cell division?
A
-all cells arise from existing cells by this process in which one cell divides into 2 identical cells
3
Q
What are the different parts of a cell? Explain them.
A
1) plasma membrane: forms the cells flexible outer surface, separating the cell’s internal and external environments
2) cytoplasm: all the cellular contents between the plasma membrane and the nucleus
- 2 components: cytosol (fluid portion) and organelles (specific shape and function)
3) nucleus: large organelle that houses most of the cell’s DNA
4
Q
Within the nucleus, each chromosome contains thousands of hereditary units called ____ that control most aspects of cellular structure and function.
A
genes
5
Q
What is the plasma membrane?
A
a flexible yet sturdy barrier that surrounds and contains the cytoplasm of a cell
6
Q
Explain the basic structural framework of the plasma membrane/ lipid bilayer.
A
- phospholipids (polar phosphate head glycerol back bone and non-polar tails)
- cholesterol (maintains fluidity)
- glycolipids
- lipid bilayer is studded with proteins (integral- channel, carrier, glycoprotein and peripheral- attach/remove itself from membrane)
7
Q
What are phospholipids?
A
- They are made up of a polar “head” that contains phosphate, which is hydrophilic
- glycerol back bone that connects tails to head
- The other part of it is made up of two long nonpolar fatty acid “tails”, which are hydrophobic
8
Q
What is cholesterol?
A
- a steroid with a hydroxyl group (-OH) attached to it (polar section of cholesterol and it produces hydrogen bonds with the heads of phospholipids and glycolipids)
- The rest of the steroid is nonpolar
9
Q
What are glycolipids?
A
- they have carbohydrate groups attached to them, which form a polar “head”.
- Their fatty acid “tails” are nonpolar.
10
Q
What are integral proteins?
A
- extend into or through the lipid bilayer among the fatty acid tails and are firmly embedded in it
- 3 types: channel, carrier and glycoprotein
11
Q
What are glycoproteins?
A
- proteins with carbohydrate groups attached to the ends
- a type of integral protein, chain of sugars attached to a protein (any protein).
- Used in signaling, allows a cell to recognize another cell
12
Q
What are peripheral proteins?
A
- on top of membrane
- attach and remove themselves from membrane
13
Q
The plasma membrane prefers letting what type of molecules through?
A
small nonpolar molecules
14
Q
The carbohydrate portions of glycolipids and glycoproteins form an extensive sugary coat called the _____. It acts like a molecular “signature” that enables cells to recognize one another.
A
glycocalyx
15
Q
Name and explain the functions of integral proteins.
A
i. Channel protein: Used to allow things to pass through cell
- do not require energy or ATP to do this.
- Go down concentration gradient
ii. Carrier protein: carries substances into/out of cell by carrying it (protecting it from other things)
- Sometimes use energy/ATP to do this.
- They can go against concentration gradient.
iii. Glycoprotein: chain of sugars attached to a protein
- Used in signaling, allows a cell to recognize another cell
16
Q
What is selective permeability?
A
-plasma membranes permit some substances to pass more readily than others
17
Q
What is a concentration gradient?
A
-a difference in the concentration of a chemical from one place to another
18
Q
What is an electrical gradient?
A
-difference in electrical charges between 2 regions
19
Q
Explain membrane potential.
A
-Because electrical gradient occurs across the plasma membrane, this charge difference is called this
20
Q
What is an eletrochemical gradient?
A
-combined influence of the concentration gradient and the electrical gradient on movement of a particular ion
21
Q
Explain passive processes. Example?
A
a substance moves down its concentration or electrical gradient to cross the membrane using only its own kinetic energy (energy of motion)
ex: simple diffusion
22
Q
Explain active processes. Example?
A
cellular energy (usually ATP) is used to drive the substance “uphill” against its concentration or electrical gradient. ex: active transport
23
Q
Explain an active process involving vesicles. Examples?
A
- tiny, spherical membrane sacs referred to as vesicles are used.
- endocytosis, in which vesicles detach from the plasma membrane while bringing materials into a cell
- exocytosis, the merging of vesicles with the plasma membrane to release materials from the cell.
24
Q
What is diffusion?
A
- a passive process in which the random mixing of particles in a solution occurs because of the particles’ kinetic energy.
25
Name factors that influence the diffusion rate of substances across plasma membranes:
- Steepness of the concentration gradient
- Temperature
- Mass of the diffusing substance.
- Surface area
- Diffusion distance
26
What is simple diffusion? What type of molecules use this process?
- a passive process in which substances move freely through the lipid bilayer of the plasma membranes of cells without the help of proteins
- Nonpolar, hydrophobic molecules like oxygen
- also, small uncharged polar molecules such as water, urea, and small alcohols
27
What is facilitated diffusion?
- an integral membrane protein assists a specific substance across the membrane.
- The integral membrane protein can be either a membrane channel or a carrier
28
What happens in channel- mediated facilitated diffusion?
- a solute moves down its concentration gradient across the lipid bilayer through a membrane channel
29
Most membrane channels are ion channels which are what?
- integral transmembrane proteins that allow passage of small, inorganic ions that are too hydrophilic to penetrate the nonpolar interior of the lipid bilayer
- Each ion can diffuse across the membrane only at certain sites.
30
In typical plasma membranes, the most numerous ion channels are selective for _____ ions or ___ ions); fewer channels are available for ___ ions or calcium ions.
- potassium, chloride
| - sodium, calcium
31
What happens in carrier-mediated facilitated diffusion?
- a carrier moves a solute down its concentration gradient across the plasma membrane
- a passive process, no cellular energy is required.
- The solute binds to a specific carrier on one side of the membrane and is released on the other side after the carrier undergoes a change in shape.
32
The number of carriers available in a plasma membrane places an upper limit, called the ____ _____, on the rate at which facilitated diffusion can occur.
transport maximum
33
Much like a completely saturated sponge can absorb no more water, the process of carrier-mediated facilitated diffusion exhibits ____
saturation
34
Substances that move across the plasma membrane by carrier- mediated facilitated diffusion include glucose, fructose, galactose, and some vitamins. Glucose, the body’s preferred energy source for making ATP, enters many body cells by carrier-mediated facilitated diffusion as follows :
1) Glucose binds to a specific type of carrier protein called the glucose transporter (GluT) on the outside surface of the membrane.
2) As the transporter undergoes a change in shape, glucose passes through the membrane.
3) The transporter releases glucose on the other side of the membrane.
35
What is osmosis?
- a type of diffusion: the movement of water molecules through a selectively permeable membrane from an area of higher water concentration to an area of lower water concentration.
36
During osmosis, water molecules pass through a plasma membrane in two ways, what are they?
(1) by moving between neighboring phospholipid molecules in the lipid bilayer via simple diffusion
(2) by moving through aquaporins, integral membrane proteins that function as water channels.
37
Osmosis occurs only when a membrane is permeable to ___ but is not permeable to certain solutes.
water
38
Explain the process of osmosis by using an experiment.
- Water molecules move through selectively permeable membrane; solute molecules in right arm cannot pass through membrane.
(a) water molecules move from the left to right arm, down water concentration gradient.
(b) volume of water in left arm has decreased and volume of solution in right arm has increased.
- At equilibrium, there is no net osmosis: Hydrostatic pressure forces just as many water molecules to move from right to left as osmosis forces water molecules to move from left to right.
(c) If pressure is applied to solution in right arm, starting conditions can be restored. This pressure, which stops osmosis, is equal to the osmotic pressure.
39
Explain tonicity.
-a measure of the solution’s ability to change the volume of cells by altering their water content
40
What is an isotonic solution?
- two solutions having the same osmotic pressure across a semipermeable membrane.
- allows for free movement of water across membrane without changing concentration of solutes on either side
41
What is a hypotonic solution?
-a solution that has less solute and more water than another solution
42
What is hemolysis?
the rupture or destruction of red blood cells
43
What is lysis?
the rupture of other types of cells due to placement in a hypotonic solution
44
What is a hypertonic solution?
-a higher concentration of solutes outside the cell than inside the cell.
45
What is crenation?
shrinkage of cells
46
What is active transport?
-an active process because energy is required for carrier proteins to move solutes across the membrane against a concentration gradient.
47
Two sources of cellular energy can be used to drive active transport:
(1) Energy obtained from hydrolysis of adenosine triphosphate (ATP) is used in primary active transport
(2) energy stored in an ionic concentration gradient is used in secondary active transport.
48
Explain primary active transport.
- energy derived from hydrolysis of ATP changes the shape of a carrier protein, which “pumps” a substance across a plasma membrane against its concentration gradient.
49
List the steps in the sodium-potassium pump.
1) 3 sodium ions in the cytosol bind to pump protein.
2) Binding of sodium ions triggers hydrolysis of ATP into ADP. This changes shape of pump protein, expelling the 3 sodium ions into extracellular fluid. New shape of pump protein favors binding of 2 potassium ions in extracellular fluid to pump protein
3) The binding of potassium ions triggers release of phosphate group from pump protein. This causes shape of pump protein to change.
4) As pump protein reverts to original shape, it releases potassium ions into the cytosol.
50
Explain secondary active transport.
- a carrier protein couples the movement of an ion (typically Na+ or H+) to drive other substances across the membrane against their own concentration gradients
- In essence, proteins harness energy in sodium ion concentration gradient by providing routes for sodium ions to leak into cells.
51
In secondary active transport, a carrier protein simultaneously binds to sodium ions and another substance and then changes its shape so that both substances cross the membrane at the same time. If these transporters move two substances in the same direction they are called ___ ; ____ , in contrast, move two substances in opposite directions across the membrane
symporters, antiporters
52
What is digitalis?
-given to patients with heart failure, a condition of weakened pumping action by the heart.
53
Explain endocytosis in a vesicle.
-materials move into a cell in a vesicle formed from the plasma membrane.
54
Explain exocytosis in a vesicle.
-materials move out of a cell by the fusion with the plasma membrane of vesicles formed inside the cell.
55
Both endocytosis and exocytosis require energy supplied by ___. Thus, transport in vesicles is an active process.
ATP
56
What is receptor-mediated endocytosis?
- is a highly selective type of endocytosis by which cells take up specific ligands.
57
Receptor-mediated endocytosis of LDLs (and other ligands) occurs as follows:
1) Binding.
2) Vesicle formation.
3) Uncoating
4) Fusion with endosome
5) Recycling of receptors to plasma membrane
6) Degradation in lysosomes
58
What is phagocytosis?
- a form of endocytosis in which the cell engulfs large solid particles, such as viruses
- vital defense mechanism that helps protect the body from disease.
59
Only a few body cells, termed phagocytes, are able to carry out phagocytosis. Two main types of phagocytes are?
1) macrophages, located in many body tissues
| 2) neutrophils, a type of white blood cell.
60
Explain the process of phagocytosis.
- particle binds to a plasma membrane receptor on phagocyte, causing it to extend pseudopods,
- Pseudopods surround the particle outside cell, and membranes fuse to form a phagosome, which enters cytoplasm.
- The phagosome fuses with one or more lysosomes, and lysosomal enzymes break down ingested material
61
What are pseudopods?
projections of a phagocyte's plasma membrane and cytoplasm.
62
In most cases, any undigested materials in the phagosome remain indefinitely in a vesicle called a ___ ____.
residual body
63
What is bulk-phase endocytosis (pinocytosis)?
- a form of endocytosis in which tiny droplets of extracellular fluid are taken up
64
Explain the process of pinocytosis.
- the plasma membrane folds inward and forms a vesicle containing a droplet of extracellular fluid.
- The vesicle detaches/ “pinches off” from the plasma membrane and enters the cytosol
- Within the cell, the vesicle fuses with a lysosome, where enzymes degrade the engulfed solutes.
65
All cells carry out exocytosis, but it is especially important in two types of cells:
(1) secretory cells that liberate digestive enzymes, hormones, mucus, or other secretions
(2) nerve cells that release substances called neurotransmitters
66
During exocytosis, membrane-enclosed vesicles called ____ vesicles form inside the cell, fuse with the plasma membrane, and release their contents into the extracellular fluid
secretory
67
What is transcytosis?
- active process in which vesicles undergo endocytosis on one side of a cell, move across the cell, and then undergo exocytosis on the opposite side
- As the vesicles fuse with the plasma membrane, the vesicular contents are released into the extracellular fluid
68
Describe the cytoplasm. What are its two main components?
- consists of all the cellular contents between the plasma membrane and the nucleus
(1) the cytosol
(2) organelles, tiny structures that perform different functions in the cell.
69
What is the cytosol?
cytosol (intracellular fluid) is the fluid portion of the cytoplasm that surrounds organelles
70
What is the cytoskeleton? What are the three types of filamentous proteins that contribute to it?
- a network of protein filaments that extends throughout the cytosol
- microfilaments, intermediate filaments, and microtubules.
71
Explain microfilaments. Composition and functions.
- thinnest elements of the cytoskeleton.
- composed of the proteins actin and myosin
-help generate movement and provide mechanical support.
-
72
Microfilaments also provide mechanical support for cell extensions called microvilli. What are they?
nonmotile, microscopic fingerlike projections of the plasma membrane
73
Name all the passive processes.
- diffusion: simple diffusion, facilitated diffusion
| - osmosis
74
Name all the active processes.
- primary active transport, secondary active transport
| - Transport in Vesicles: Receptor-mediated endocytosis, Phagocytosis, Bulk-phase endocytosis, Exocytosis, Transcytosis
75
Explain the difference between passive and active processes.
- passive: Movement of substances down a concentration gradient until equilibrium is reached; do not require cellular energy in the form of ATP.
- active:Movement of substances against a concentration gradient; requires cellular energy in the form of ATP.
76
Explain intermediate filaments.
- thicker than microfilaments but thinner than microtubules
- found in parts of cells subject to mechanical stress; they help stabilize the position of organelles such as the nucleus and help attach cells to one another.
77
Explain microtubules.
- largest of the cytoskeletal components and are long, unbranched hollow tubes composed mainly of the protein tubulin.
- assembly of microtubules begins in the centrosome
- help determine cell shape
78
What are organelles?
-specialized structures within the cell that have characteristic shapes, and they perform specific functions in cellular growth, maintenance, and reproduction
79
What is a centrosome? What are its two components?
- located near the nucleus, consists of two components: a pair of centrioles and pericentriolar material
80
Explain the two components of a centrosome. A pair of centrioles and pericentriolar material:
- two centrioles are cylindrical structures, each composed of 9 clusters of 3 microtubules (triplets) arranged in a circular pattern
- Surrounding the centrioles is pericentriolar material, which contains hundreds of ring-shaped complexes composed of the protein tubulin which makes the spindles grow in mitosis
81
What is cilia and its function? Ex?
- are numerous, short, hairlike projections that extend from the surface of the cell
- Cilia move fluids along a cell’s surface.
- ex: Cilia lining the trachea
82
What is flagella and its function? Ex?
- similar in structure to cilia but are typically much longer.
- A flagellum moves an entire cell.
- ex: sperm cell's tail
83
What are ribosomes? 2 functions
- the sites of protein synthesis
- high content of ribosomal RNA (rRNA)
1) Ribosomes associated with endoplasmic reticulum synthesize proteins destined for insertion in the plasma membrane or secretion from the cell.
2. Free ribosomes synthesize proteins used in the cytosol.
84
What is the endoplasmic reticulum (ER)?
- a network of membranes in the form of flattened sacs or tubules
- extends from the nuclear envelope (membrane around the nucleus), to which it is connected, throughout the cytoplasm.
85
Cells contain two distinct forms of endoplasmic reticulum (ER), which differ in structure and function. Name and explain them.
- Rough ER is synthesizes glycoproteins and phospholipids that are transferred into cellular organelles, inserted into the plasma membrane, or secreted during exocytosis
- Smooth ER synthesizes fatty acids and steroids, inactivates or detoxifies drugs and other potentially harmful substances
86
What happens in the golgi complex?
- Modifies, sorts, packages, and transports proteins received from the rough ER
- Forms secretory vesicles that discharge processed proteins via exocytosis intoextracellular fluid; forms membrane vesicles that ferry new molecules to the plasma membrane; forms transport vesicles that carry molecules to other organelles, such as lysosomes
87
What is the golgi complex made up of?
- consists of 3 to 20 cisternae
- The cisternae at the opposite ends of a Golgi complex differ from each other in size, shape, and enzymatic activity. -The convex entry (cis face) is a cisterna that faces the rough ER.
- The concave exit (trans face) is a cisterna that faces the plasma membrane.
- Sacs between the entry and exit faces are called medial cisternae.
88
Proteins arriving at, passing through, and exiting the Golgi complex do so through maturation of the cisternae and exchanges that occur via transfer vesicles. List the steps:
1) Formation of transport vesicles
2) Transport vesicles move to entry face of Golgi complex.
3) Fusion of vesicles creates entry face of Golgi complex and releases proteins into its lumen
4) Transfer vesicles move enzymes back toward entry face and move some partially modified proteins toward exit face.
5) products of the medial cisternae move into the lumen of exit face
6) Within the exit face cisterna, the products are further modified and sorted/packaged
7) Some of the processed proteins leave exit face and stored in secretory vesicles.
8) Other processed proteins leave exit face in membrane vesicles that deliver their contents to plasma membrane for incorporation into membrane.
9) some processed proteins leave the exit face in transport vesicles that will carry the proteins to another cellular destination.
89
What are lysosomes?
- are membrane-enclosed vesicles that form from the Golgi complex
- contains digestive enzymes
90
What are the functions of lysosomes? (4)
1. Digest substances that enter a cell via endocytosis and transport final products of digestion into cytosol.
2. Carry out autophagy, the digestion of worn-out organelles.
3. Implement autolysis, the digestion of an entire cell.
4. Accomplish extracellular digestion
91
Explain autophagy.
The process by which entire worn-out organelles are digested
92
What is an autophagosome?
In autophagy, the organelle to be digested is enclosed by a membrane derived from the ER to create a vesicle called an autophagosome, the vesicle then fuses with a lysosome
93
What is autolysis?
when Lysosomal enzymes destroy the entire cell that contains them
94
What is Tay-Sachs disease?
-an inherited condition characterized by the absence of a single lysosomal enzyme called Hex A
95
What are peroxisomes?
-contain several oxidases, enzymes that can oxidize (remove hydrogen atoms from) various organic substances.
96
What are proteasomes?
- Continuous destruction of unneeded, damaged, or faulty proteins is the function of tiny barrel- shaped structures consisting of four stacked rings of proteins around a central core called proteasomes
- contain myriad proteases, enzymes that cut proteins into small peptides.
97
What is the mitochondria?
- powerhouse of the cell
- consists of an outer mitochondrial membrane and an inner mitochondrial membrane with a small fluid-filled space between them
98
The inner mitochondrial membrane contains a series of folds called ____ _____
mitochondrial cristae
99
The central fluid-filled cavity of a mitochondrion, enclosed by the inner mitochondrial membrane, is the ______ ______ .
mitochondrial matrix
100
What is apoptosis?
-the orderly, genetically programmed death of a cell.
101
What are the functions of the mitochondria?
1. Generate ATP through reactions of aerobic cellular respiration.
2. Play an important early role in apoptosis.
102
What does the nuclear envelope do?
separates the nucleus from the cytoplasm
103
What do nuclear pores do?
-control the movement of substances between the nucleus and the cytoplasm.
104
What do nucleoli do?
spherical bodies in the nucleus that function in producing ribosomes.
105
What do genes do?
control cellular structure and direct cellular activities.
106
Genes are arranged along ____? Human somatic (body) cells have __ chromosomes, ___ inherited from each parent. Each chromosome is a long molecule of DNA that is coiled together with several proteins. This complex of DNA, proteins, and some RNA is called _____
chromosomes, 46, 23, chromatin
107
What are the functions of a nucleus?
1. Controls cellular structure.
2. Directs cellular activities.
3. Produces ribosomes in nucleoli.
108
The total genetic information carried in a cell or an organism is its _____
genome
109
Chromatin has a beads-on-a-string structure. Each bead is a ______ that consists of double-stranded DNA wrapped twice around a core of 8 proteins called _____, which help organize the coiling and folding of DNA. The string between the beads is called _____ ___, which holds adjacent nucleosomes together. In cells that are not dividing, another histone promotes coiling of nucleosomes into a larger-diameter ____ _____ , which then folds into large loops. Just before cell division takes place, however, the DNA replicates (duplicates) and the loops condense even more, forming a pair of ______.
- nucleosome, histones, linker DNA
| - chromatin fiber, chromatids
110
What are proteomes?
-refers to all of an organism’s proteins
111
What is gene expression?
- a gene’s DNA is used as a template for synthesis of a specific protein.
- transcription then translation
112
DNA and RNA store genetic information as sets of three nu- cleotides. A sequence of three such nucleotides in DNA is called a ___ ____. Each DNA base triplet is transcribed as a complementary sequence of three nucleotides, called a _____. The ____ _____ is the set of rules that relate the base triplet sequence of DNA to the corresponding codons of RNA and the amino acids they specify.
base triplet, codon, genetic code
113
In terms of gene expression, explain the first step: transcription.
- sequence of base triplets in DNA serves as a template for copying the info into a complementary sequence of codons.
-3 types of RNA are made from DNA template:
1) Messenger RNA directs protein synthesis
2) Ribosomal RNA joins ribosomal proteins to
make ribosomes.
3) Transfer RNA binds to amino acid and holds it in place on ribosome until incorporated into a protein
- One end of tRNA carries specific amino acid, and opposite end has an anticodon.
- the tRNA anticodon attaches to the mRNA codon
114
What does the enzyme RNA polymerase do?
-catalyzes transcription of DNA.
115
The segment of DNA where transcription begins, a special nucleotide sequence called a ____, is located near the beginning of a gene
promoter
116
During transcription, bases pair in a complementary manner: The bases cytosine (C), guanine (G), and thymine (T) in the DNA template pair with _______, _____, ____ respectively, in the RNA strand. However, adenine in the DNA template pairs with _____, not thymine, in RNA:
- guanine, cytosine, and adenine (A)
| - uracil (U)
117
Transcription of the DNA strand ends at another special nucleotide sequence called a _____ , which specifies the end of the gene
terminator
118
What are introns and exons?
- Regions within a gene called introns do not code for parts of proteins.
- They are located between regions called exons that do code for segments of a protein.
- Immediately after transcription, the transcript includes information from both introns and exons and is called pre-mRNA.
119
The introns are removed from pre- mRNA by small nuclear ribonucleoproteins. How do they do this?
- The snRNPs are enzymes that cut out the introns and splice together the exons.
- The product is a functional mRNA molecule that passes through a pore in the nuclear envelope to reach the cytoplasm, where translation takes place
120
What is alternative splicing of mRNA?
- a process in which the pre- mRNA transcribed from a gene is spliced in different ways to produce several different mRNAs
121
In terms of gene expression, explain the second step: translation.
- an mRNA molecule binds to a ribosome.
- Then, the mRNA nucleotide sequence specifies the amino acid sequence of a protein.
- Ribosomes have a binding site for mRNA and a P site and an A site for attachment of tRNAs.
122
Several ribosomes attached to the same mRNA constitute a _________
polyribosome
123
What are the two types of cell division?
somatic cell division and reproductive cell division
124
What is a somatic cell? What is a germ cell?
- any cell other than germ cell
| - a gamete (sperm or oocyte) or any precursor cell destined to become a gamete
125
Somatic cell division, a cell undergoes a nuclear division called ____ and a cytoplasmic division called _____ to produce two genetically identical cells, each with the same number and kind of chromosomes as the original cell.
mitosis, cytokinesis
126
Reproductive cell division is the mechanism that produces gametes, the cells needed to form the next generation of sexually reproducing organisms. This process consists of a special two- step division called ___, in which the number of chromosomes in the nucleus is reduced by half
meiosis
127
The cell cycle is a sequence of events in which a somatic cell duplicates its contents and divides in two. Human cells contain 23 pairs of chromosomes, for a total of 46. One member of each pair is inherited from each parent. The two chromosomes that make up each pair are called ____ ____
homologous chromosomes
128
When examined under a light microscope, homologous chromosomes generally look very similar. The exception to this rule is one pair of chromosomes called the sex chromosomes. What do they look like?
- In females the homologous pair of sex chromosomes con- sists of two large X chromosomes
- in males the pair consists of an X and a much smaller Y chromosome
129
Because somatic cells contain two sets of chromosomes, they are called ____ cells, symbolized __.
diploid, 2n
130
The cell cycle consists of two major periods:____, when a cell is not dividing, and the ____ phase, when a cell is dividing
interphase, mitotic
131
Explain interphase and its 3 phases: G1, S and G2. (s-synthesis, g-gap)
- G1: Cell metabolically active; duplicates organelles and cytosolic components, centrosome replication begins
- S: DNA replicated
- G2: Cell growth continues; enzymes and other proteins are synthesized; centrosome replication completed
132
Explain the phases of mitosis.
- Prophase: Chromatin fibers condense into paired chromatids; nucleolus and nuclear envelope disappear; each centrosome moves to an opposite pole of the cell.
- Metaphase: Centromeres of chromatid pairs line up at metaphase plate.
- Anaphase: Centromeres split; identical sets of chromosomes move to opposite poles of cell.
- Telophase: Nuclear envelopes and nucleoli reappear; chromosomes resume chromatin form; mitotic spindle disappears
133
What happens in cytokinesis?
Cytoplasmic division; contractile ring forms cleavage furrow around centre of cell, dividing cytoplasm into separate and equal portions.
134
What do cyclin-dependent protein kinases (Cdk’s) do?
- transfer a phosphate group from ATP to a protein to activate the protein
- The activation and deactivation of Cdk’s at the appropriate time is crucial in the initiation and regulation of DNA replication, mitosis, and cytokinesis.
135
What are cyclins responsible for?
Switching the cyclin-dependent protein kinases (Cdk’s) on and off is the responsibility of these cellular proteins
136
What is the difference between apoptosis and necrosis?
Apoptosis, a genetically programmed death, is a normal type of cell death; in contrast, necrosis is a pathological type of cell death that results from tissue injury.
137
Unlike mitosis, which is complete after a single round, meiosis occurs in two successive stages: meiosis I and meiosis II. Meiosis I, which begins once chromosomal replication is complete, consists of four phases: prophase I, metaphase I, anaphase I, and telophase I. Explain meiosis I.
- prophase I: chromosomes shorten and thicken, the nuclear envelope and nucleoli disappear, and the mitotic spindle forms.
- the two sister chromatids of each pair of homologous chromosomes pair off, called synapsis
- The resulting 4 chromatids form a tetrad.
- metaphase I: tetrads line up along the metaphase plate of the cell, with homologous chromosomes side by side
- anaphase I, the members of each homologous pair of chromosomes separate as they are pulled to opposite poles of the cell. The paired chromatids, held by a centromere, remain together.
- Telophase I and cytokinesis of meiosis are similar to those of mitosis.
138
Explain meiosis II.
- consists of 4 phases: prophase II, metaphase II, anaphase II, and telophase II
- These phases are similar to those that occur during mitosis; the centromeres split, and the sister chromatids separate and move toward opposite poles of the cell
139
Meiosis I begins with a diploid starting cell and ends with two cells, each with the ____ number of chromosomes. During meiosis II, each of the two haploid cells formed during meiosis I divides; the net result is four haploid_____ that are genetically different from the original diploid starting cell.
haploid, gametes
140
What are telomeres?
- specific DNA sequences found only at the tips of each chromosome.
- These pieces of DNA protect the tips of chromosomes from erosion and from sticking to one another.
