Chapter 3: Chemical Level of Organization: Cells And Homeostasis Flashcards
1
Q
What is a plasma membrane?
A
Cell’s outer surface surrounding the cell internal’s and external organs
2
Q
What is the cytoplasm?
A
Consists of all the cell’s cellular contents between the plasma membrane and nucleus. Contains 2 parts: Cytosol (fluid portion of cytoplasm, contains water, dissolved solvents, suspended particles), and organelles (Characteristic shape and function).
3
Q
What is the nucleus?
A
Contains most of cell’s DNA. Each chromasome within has thousands of genes that control most aspects of a cell’s structure and function.
4
Q
What is the fluid-mosaic model?
A
The molecular arrangement of the plasma membrane resembles a continually moving sea of fluid lipids that contain a mosaic of different proteins
5
Q
What are the 4 functions of the plasma membrane?
A
1) Acts as a barrier separating inside or outside of cell. 2) Controls the flow of substances into and out of cell. 3) Helps identify the cell to other cells (eg immune cells) and 4) Participates in intercellular signalling
6
Q
Describe the basic structure of the lipid bilayer
A
2 back-to-back layers made up of 3 types of lipid molecules: Phospholipids (75%… contains phosphorus), cholesterol (20%… steriod with attached OH group) and glycolipids (5%… attahched carbohydrate group)
7
Q
How do phospholipids orient themselves in the lipid bilayer?
A
Their hydrophilic heads face outward… the heads face a watery fluid on either side (cytosol on the inside and EC fluid on the outside). Hydrophobic fatty acid tails in each half of the bilayer point toward one another forming a nonpolar hydrophobic region in the membrane’s interior
8
Q
What are integral proteins?
A
Extended into or through the lipid bilayer and firmly embedded in it. Most are transmembrane proteins so extend the entire width of the bilayer and portrude into both the cytosol and the EC fluid. Example are glycoproteins (proteins with carbohydrate groups attached to the ends that protrude into the EC fluid. The carbohydrates are oligosaccharides)
9
Q
What is peripheral proteins?
A
Not as firmly embedded in the membrane. Attached to the polar heads of membrane lipids or integral proteins at the inner or outer surface of the membrane.
10
Q
What is Glycocalyx?
A
Carbohydrate portions of glycolipids and glycoproteins that form an extensive sugary glyccalyx. Enables cells to recognize one another (ie WBCs ability to detect a foreign glycocalyx).
11
Q
What are the 5 functions of integral proteins?
A
1) ion channels (pores/holes that specific ions can flow through to can into/out of cell). 2) Carriers (Selectively moving a polar substance or ion from one side of the memebrane to the other). 3) Receptors (Recognizes and binds a specific types of molecules. Insulin receptors bind insulin. A molecule that binds to a receptor is called a LIGAND). 4) Enzymes (catalyze specific chemical reactions). 5) Linkers (Anchor proteins in plasma membranes of nearby cells to one another or to protein filaments inside and outside of cell)
12
Q
What’s a main function of glycoproteins and glycolipids?
A
Serve as identity markers. May enable a cell to 1) recognize other cells of the same kind during tissue formation and 2) Recognize and respond to foreign dangerous cells. Eg blood cells must be compatible or RBCs will clump together.
13
Q
Functions of peripheral proteins?
A
1) Support plasma membrane. 2) Anchor integral proteins. 3)Move materials and organelles within cells. 4) Attach cells to one another.
14
Q
What does membrane fluidity depend on?
A
The number of double bonds in the fatty acid tails of the lipids in the bilayer. Each double bond puts a kink in the fatty acid tail which increases membrane fluidity by preventing lipid molecules from packing together
15
Q
Why is membrane fluidity important?
A
Enables movement of membrane materials responsible for important cell processes like cell movement, growth, division, and secretion. It also allows it to self-seal when punctured or torn (ie intracytoplasmic sperm injection).
16
Q
How does cholesterol’s affect on the lipid bilayer vary based on temperature?
A
Makes lipid bilayer stronger (and less fluidity) at normal temperature and weaker (and more fluidity) at lower temperature
17
Q
What is selective permeability?
A
The plasma membrane allows some substances t pass more readily than others. Nonpolar molecules (CO2, O2, steriods) are highly permeable, moderately permeable to small uncharged polar molecules (water and urea) and impermeable to large uncharged polar molecules (like glucose). Transmembrane proteins that act as channels and carriers can increase the plasma membrane’s permeability to a variety of selective ions and uncharged polar molecules.
18
Q
What’s a concentration gradient?
A
A difference in the concentration of a chemical from one place to another. Like from outside the cell to inside.
19
Q
What is ELECTRICAL GRADIENT and MEMBRANE POTENTIAL?
A
The inner surface of the plasma membrane is more negatively charged and the outer surface is more positively charged. This difference in electrical charges is called an electrical gradient. The charge difference is termed membrane potential.
20
Q
What’s the electrochemical gradient?
A
A substance will move downhill from where it’s more concentrated to where it’s less concentrated to reach equilibrium. A positively charged substance will move towards a negatively charged substance and vice versa. The combined influence of the concentration gradient and electrical gradient is the electrochemical gradient.
21
Q
WHat are passive processes?
A
A substance moves down its concentration / electrical. Gradient to cross the membrane using only its own kinetic energy (energy of motion) no input from cell’s energy. Example is simple diffusion
22
Q
What are active processes?
A
Cellular energy is used to drive the substance uphill against its concentration or electrical gradient. ATP is used. Example is active transport.
23
Q
What are endocytosis and exocytosis?
A
They are active processes using the vesicles. In endocytosis, vesicles detach from the plasma membrane while bringing materials into a cell0. In exocytosis vesicles merge with the plasma membrane to release materials from the cell.
24
Q
WHat is diffusion?
A
A passive process. Random mixing of particles occurs in a solution because of the particles’ kinetic energy. Both solutes and solvents undergo diffusion. Solute molecules will diffuse towards an area of low concetration (think about the dye example)… eventually they become evenly distributed and reach equilibrium
25
Factors that influence the diffusion rate of substances across a membrane
1) Steepness of concentration gradient (greater the difference in concentration between tthe 2 sides of the membrane the higher the rate of diffusion). 2) Temperature (the higher the temp the faster the rate of diffusion). 3) Mass of the diffusing substance (the larger the mass of the diffusing particle the slower the diffusion rate). 4) Surface area (The larger the membrane SA available for diffusion the faster the rate of diffusion... air sacs of lungs). 5) Diffusion distance (The greater the distance over which diffusion must occur the longer it takes... pneumonia).
26
What is simple diffusion?
Passive process. Substances move freely through the lipid bilayer of the plasma membrane of cells without the help of membrane transport proteins. Like nonpolar hydrophobic molecules. O, CO2, N gases, steriods, fatty acids, fat soluble vitamins, small uncharged polar molecules like water and urea
27
What is facilitated diffusion?
An integral membrane protein (either a membrane channel or carrier) assists a specific substance across a membrane. Usually solutes that are too polar or highly charged
28
What's channel-mediated facilitated diffusion?
A solute moves down its concentration gradient across the lipid bilayer through a membrane channel (likely an ion channel)... passage of small inorganic molecules too hydrophilic to penetrate the nonpolar interior of the lipid bilayer
29
What's a gated channel?
When a part of the channel acts as a gate or a plug, changing shape in one way to open to pore and another to close
30
What's carrier-mediated facilitated diffusion?
A carrier moves a solute down its concentration gradient across the plasma membrane. Passive so no cell energy required. Solute binds to specific carrier on one side of membrane and is released on other side. The rate of carrier mediated fac diffusion is determined by the steepness of the concentration gradient across the membrane.
31
What is the transport maximum?
The upper limit on the rate that facilitated diffusion occurs. Once all carriers are occupies the transport maximum is reached... this is called saturation when this happens. A
32
Describe how glucose diffuses
1) Glucose binds to a specific protein called glucose transporter on the outside of the membrane. 2) As the transporter uundergoes changes in shape glucose passes through the membrane. 3) The transporter releases glucose on the other side of the membrane
33
What is osmosis?
Water molecules moving through a plasma membrane from an area of higher concentration to an area of lower concentration. NET MOVEMENT OF WATER MOLECULES
34
What are the 2 ways in which water passes through a plasma membrane?
1) By moving between neighbouring phospholipids in the lipid bilayer via simple diffusion or 2) by moving through aquaporins (integral membrane proteins that function as water channels)
35
What is hydrostatic pressure?
The higher the column of solution in the right arm becomes, the more pressure it exerts on its side of the membrane and water molecules are forced back into the left arm. Equilibrium is reached when just as much water molecules move from right to left due to hydrostatic pressure as move from left to right due to osmosis.
36
What is osmotic pressure?
The solution with the impermeable solute also exerts a force (osmotic pressure) which is proportional to the concentration of solute particles that can't cross the membrane. So the higher the solute's concentration the higher the osmotic pressure. It's the pressure needed to stop the movement of water from left tube into right
37
What is Tonicity?
A measre of the solution's ability to change the volume of cells by altering their water content. An ISOTONIC SOLUTION is any solution in which a cell maintains its normal shape and volume
38
Define hypotonic solution
A solution that has a LOWER concentration of solutes than the cutosol inside the RBCs... water enters faster than it leaves. RBCs swell and may burst (hemolysis)
39
Define Hypertonic solution
A higher concentration of solutes in solution than the cytosol inside the RBCs so cells shrink (crenation)
40
What is Active transport?
Against the concentration gradient. Energy required for carrier proteins to move solutes across the membrane against their concentration gradient.
41
WHat are the 2 sources of cellular energy to drive ACTIVE TRANSPORT?
1) energy obtained from the hydrolosys of ATMP (Primary active transport). 2) Energy stored in an ionic concentration gradient (secondary active transport)
42
What is 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. Like cyanide turns off ATP production so is lethal
43
What's the sodium-potassium pump?
Expels NA+ ions from cells and brings K+ ions in. Maintains low concentration of NA+ ions in cytosol by pumping these ions into the EC fluid against the Na+ concentration gradiant. Pumps K+ into cells against K+ gradient. Maintains low concentration of sodium and high concentration of potassium
44
What is secondary active transport?
The energy stored in Na or H concentration gradient is used to drive other substances across the membrane against their own cncentration gradient. Indirectly uses ATP because Na and H gradient is established by primary active transport. The Na-K pump maintains a steep concentration gradient of Na+ across the plasma membrane so the Na ions have stored / potential energy... like water behind a damn. . STored energy converted to kinetic and transport other substances against their concentration gradient. A carrier protein simultaneously binds to Na and other substance and then changes shape so that both substances cross the membrane at the same time.
45
What are symporters?
If the transporters move 2 substances in the same direction across the membrane (secondary active transport)
46
What are antiporters?
Opposite direction across the membrane. Na+ H+ antiporters help regulate blood pH by expelling excess H. Calcium ions low in cytosol because antiporters eject them.
47
What are the 3 types of endocytosis?
receptor-mediated endocytosis, phagocytosis, and bulk-phase endocytosis
48
What is endocytosis and what are its steps?
A vesicle forms after a receptor protein in the plasma membrane recognizes and binds to a particle in the EC fluid in the EC fluids. There are 6 steps. 1) BINDING: An LDC particle that contains cholesterol binds to a specific receptor in the plasma membrane to form a receptor-LDL complex. The receptors are integral membrane proteins concentrated in regions of the plasma membrane called clathrin-coated pits. 2) VESICLE FORMATION: The invaginated edges of the membrane around the clathrin-coated pit fuse and a small piece of membrane pinches off. 3) UNCOATING: The clathrin-coated vesicle loses its clathrin coat to become an uncoated vesicle. 4) FUSION WITH ENDOSOME: Uncoated vesicle quickly fuses with a vesicle known as the endosome (within the endosome the LDL particles separate from the receptors). 5) RECYCLING OF RECEPTORS TO PLASMA MEMBRANE: Transport vesicles return the receptors to the plasma membrane. 6) DEGRADATION IN LYSOSOMES: Other transport vesicles, which contain the LDL particles, bud off the endosome and soon fuse with a lysosome. The lysosomes contain digestive enzymes and certain enzymes break down the large protein and lipid molecules of LDL particle into amino acids, fatty acids, and cholesterol. These smaller molecules leave the lysosome.
49
Describe Phagocytosis
Cell engulfs large solid particles like worn-out cells, bacteria, viruses etc. Phagocytes (macrophages and neutrophils) carry out phagocytosis. A particle binds to a plasma membrane receptor on the phagocyte causing it to extend pseudpods (projecyions of its plasma membrane and cytoplasm). Pseudopods surround the particle outside the cell and the membranes fuse to vesicles called phagosomes, which enters the cytoplasm. Phagosome fuses with lysosomes and lysosomal enzymes break down injested material
50
What is bulk-phase endocytosis?
Tiny droplets of EC fluid are taken up. No receptor proteins. Solutes dissolved in the EC fluid are brought into the call. Plasma membrane folds inward and forms a vesicle containing a droplet of EC fluid. Vesicle detaches from the plasma membrane and enters the cytosol. Vesicle fuses with a lysosome where enzymes degrade engulfed solutes. Occurs in most cells but especially in absorptive cell like intestines and kidneys.
51
What is exocytosis?
Releases material from a cell. Secretory vesicles form inside the cell, fuse with plasma membrane and releases their contents into the EC fluid
52
What's transcytosis?
Vesicles undergo undercytosis on one side of the cell, transport in vesicles across the cell and undergo exocytosis on the opposite side. . As a means for materal to move between blood plasma and interstitial fluid
53
What is the cytoskeleton?
Network of protein filaments that extends throughout the cytosol (microfimalements, intermediate filaments, microtubules)
54
What are microfilaments?
Thinnest elements of cytoskeleton. Composed of actin and myosin and most prevalent at edge of cell. Helps generate mvement (muscle contractions, cell division and locomotion like cell migration). Provides mechanical support (basic strength and shapes of cells, Anchors cytoskeleton to integral proteins in the plasma membrane. Provides support for cell extensions called microvilli
55
What are intermediate filaments?
Helps stabalize the position of organelles like the nucleus and help attach cells to one another
56
What are microtubules?
Largest cytoskeletal component. Long unbranched hollow tubes composed mainly of the protein tubulin. Grows outward from the centrosome toward the periphery of the cell. Helps determine cell shape. Helps in the movement of secretory vesicles, chromosomes during cell division and of specialized projections (clilia and flagella).
57
What is the centrosome of the cell?
It's near the nucleus and has 2 parts: the 2 centrioles and the pericentriolar material. The 2 centrioles are cylindrical and composed of 9 clusters of 3 microtubules arranged in a circular pattern. The pericentriolar material has hundreds of ring shaped complexes composed of tubulin. The tubulin is the organizing centres for growth of the mitotic spindle and for microtubule formation in nondividing cells.
58
What are the cilia and flagella in cells?
Projections from the cell surface. Cilia are numerous hairlike projections that are anchored to basal bodies (similar in structure to a centriole and initiates the assembly of cilia and flagella). A cilium displays an oarlike pattern of beating.... relatively stiff during the powerstroke and flexible during recovery. This coordination allows for steady movement of fluid along the cell's surface (ie hundreds of cilia help sweep away foreign particles trapped in mucus away from lungs). FLAGELLA is much longer and moves the entire sell. It rapidly wiggle its tail in a wave like pattern.
59
What are ribosomes in cells?
Site of protein synthesis. Synthesize proteins destined for specific organelles, for insertion in the plasma membrane or for export from cell. Divided into large and small subunits. Some are attached to the outer surface of the nuclear membrane and to the ER. Others are free ribosomes an unattachd to other cytoplasmic structures (they synthesize proteins used in the cytosol).
60
What is the endoplasmic reticulum of the cell?
Network of membranes in the form of flattened sacs or tubules.
61
What is the rough ER of the cell?
Continuous with nuclear membrane. Folded into a series of flattened sacs. Outer surface studded with ribosomes (the proteins synthesized by these ribosomes enter spaces in the ER for processing and sortin). Produces secretory proteins, membrane proteins and many organelle proteins. Enzymes may attach the proteins to carbohydrates to form glycoproteins or the enzzymes may attach the proteins to phospholipids
62
What is the smooth ER of the cell?
Extends from rough ER to form a network of membrane tubules. No ribosomes on outer surface so does not synthesize proteins. Synthesizes fatty acids and steriods (like estrogen and testosterone). In liver cells the smooth ER helps release glucose to the blood stream and inactivate/detoxify lipid soluble drugs (like alcohol)
63
What is the golgi complex?
Transport pathway for synthesize proteins. Consists of 3-20 citernae (small, flattened membranous sacs). More extensive in cells that secret proteins. The CONVEX ENTRY FACE is a cisternae that faces the rough ER. It recieves and modifies proteins produced by the rough ER. The MEDIAL CISTERNAE adds carbohydrates to proteins to form glycoproteins and lipids to proteins to form lipoproteins. The EXIT FACE is a cisternae that faces the plasma membrane. It modifies the molecules further and sorts and packages them for transport to their destination. Some processed proteins leave the exit face and are stored in the secretory vesicles (the secretory vesicles then deliver them to the plasma membrane and they exit to the EC via exocytosis).
64
What are the lysosomes of the cell?
Membrane enclosed vesicles that form from the golgi complexes. Can contain up to 60 kinds of powerful digestive and hydrolytic enzymes that break down molecules once lysosomes Fuse with vesicles formed during endocytosis. Works best in acidic environment so a transport pump imports H+ ions. Engulfs another organelle, digests it and returns the digested components to the cytosol for reuse. Lysosomal enzymes may destroy the entire cell that contains them (autolysis). Some operate in extracellular digestion (ie during fertilization a sperm cell releases lysosomal enzymes that aid its penetration of the oocyte by dissolving its protective coating)
65
What are autophagosomes?
The organelle to be digested by a lysosome is enclosed by a membrane derived from the ER to create a vesicle called an autophagosome... the vesicle fuses with the lysosome.
66
What are peroxisomes of the cell?
Aka microbodies. Contains oxidases (enzymes that oxidize (remove atoms from) various organic substances). Amino acids and fatty acids are oxidized in peroxisomes as part of normal metabolic processes. Oxidize toxic substances like alcohol (so abundant in liver). Hydrogen peroxide is a toxic compound associated with free radicals like superoxide which is a byproduct of oxidation. But contins catalase which decomposes H2O2 and enzymes to destroy superoxide.
67
What are proteasomes?
4 stacked rings of proteins around a central core. Continuous destruction of unneeded, damaged or faulty proteins. Proteins that are part of the metabolic pathway need to be degraded after they have accomplished their function... halts a pathway once the response has been acheived (plays a part in negative feedback). Many thousand proteasomes in the cytosol and nucleus. Contains proteasol, chich are enzymes that cut proteins into small peptides.
68
What is the mitochondria of the cell?
Powerhouse. Generates most ATP through aerobic respiration. Active cells that use ATP at a high rate (like liver and kidney cells) have a large number of mitochondria. Regular exercise leads to an increase in number of mitochondria. Usually located in the cell where the oxygen enters or the ATP is used. Constsists of the outer mitochondrial membrane and the inner mitochondrial membrane. The inner mitochondrial membrane consists of a series of folds called mitochondrial cristae. These folds provide a huge SA for the chemical reactions that are part of aerobic respiration to take place. The enzymes that catalyze these reactions are located in the folds. Also plays an early role in apoptosis.
69
Describe the nucleus and the parts of it
RBCs don't have one. But skeletel muscles and a few others have several. The NUCLEAR ENVELOPE separates the nucleus from the cytoplasm and made of lipid bilayers like in plasma membrane. The NUCLEAR PORES are found throughout the envelope. They control the movement of substances between cytplasm and nucelus. Small molecules and ions move through pores by passive diffusion. Larger molecules (RNA and proteins) pass through active transport. The NUCLEOLI is spherical and produces ribosomes. Each nucleolus is a cluster of protein, DNA and RNA... it's not enclosed by a membrane. Site of synthesis of rRNA and assembly of rRNA and proteins into ribosomal subunits... prominant in cells that synthesize a lot of proteins like muscle and liver.
70
What is chromatin?
Has a Beads-on-a-string structure. Each bead is a nucelosome that consists of double stranded DNA wrapped twice around a core of 8 proteins called histones (they help organize the coiling and folding of DNA). The string between the beads is called linker DNA which holds adjacent nucleosomes together. Another histone promotes the coiling of nucleosomes into a larger chromatin-fiber (which folds into loops). Just before cell division, DNA duplicates and forms a pair of chromatids (2 chromatids = 1 chromosome)
71
What is gene expression?
A gene's DNA is used as a template for synthesis of specific proteins
72
What is transcription and translation?
Transcription is info encoded in a region of DNA is transcribed (copied) to produce a molecule of RNA. Translation is RNA attaches to a ribosome where the info in RNA is translated in a corresponding sequence of amino acids to form a new protein.
73
What's a base triplet?
A sequence of 3 nucleotides in DNA
74
What's a codon?
Each DNA base triplet is transcribed as a complementary sequence of 3 nucleotides . A codon specifies an amino acid
75
What's a genetic code?
Rules that relate the base triplet sequence of DNA to the corresponding codons of RNA and the amino acids.
76
Where does transcription take place and what serves as a template for it?
Nucleus. And the info represented by the base triplets in DNA serve as a template for copying the info into a complementary sequence of codons.
77
What are the 3 types of RNA?
1) Messenger RNA (mRNA): Directs synthesis of a protein. 2) Ribosomal RNA (rRNA): Joins with ribosomal proteins to make ribosomes. 3) Transfer RNA (tRNA): Binds to an amino acid and holds it in place on a ribosome until it's incorporated into a protein during translation.
78
What RNA Polymerase?
Catalyzes transcription of RNA. Only 1 of 2 DNA strands serves as template for RNA synthesis.
79
What's a promoter?
A segment of DNA (a nucleotide sequence) near beginning of the gene where transcription starts. Where RNA polymerase attaches to DNA.
80
What's the terminator?
A nucleotide sequence where transcription of DNA ends... end of gene. Where RNA polymerase reaches the terminator the enzymes detach from the transcribed RNA
81
What are introns?
Regions of a gene that don't code for parts of proteins
82
What are exons?
Lie on either side of introns and do code for proteins.
83
What is pre-mRNA?
Right after transcription the transcrip includes info from introns and exons
84
What are small nuclear ribonucelo proteins (snRNPs)?
Enzymes that cut out introns and splice together exons
85
Why do we have so many proteins?
Alternate splicing of mRNA. Pre-mRNA transcribed from a gene is spliced in different ways to produce several different mRNAs which are then translated to proteins. Also, chemical alterations in the golgi complex can produce 2 or more different proteins for one translation.
86
What part of a cell carries out translation?
Ribosomes
87
What does a small subunit in a ribosome do in translation?
Has a binding site for mRNA
88
The large subunit of a ribosome has 3 binding sits for mRNA. What are they called and what do they do?
1) P (peptidyl) site binds the tRNA carrying th growing polypeptide chain. 2) A (aminoacyl) site binds the tRNA carrying the ext amino acid to be added to the growing polypeptide chain. 3) E (exit) site binds the tRNA just before it's released from ribosome
89
What's a polyribosome?
Several ribosomes attached to the same mRNA... leads to translation of 1 mRNA into several identical proteins at same time
90
What's the purpose of somatic cell division and what are the 2 types?
It is meant to replace dead or injured cells and add new ones during tissue growth. A cell undergoes nuclear division (mitosis) and cytoplasmic division (cytokinesis)
91
What's the purpose of reproductive cell division and what's it called?
Produces gametes. It's called meiosis
92
What are somatic cells called diploid cellls?
Because they contain 2 sets of chromosomes.
93
What are the 2 main phases of cell division?
Interphase (cell not dividing) and mitotic phase (cell dividing)
94
What happens in interphase?
Cell replicates its DNA. Produces additioal organelles and cytosolic components in anticipation for cell division. High metabolic activity. Where cell does most of its growing. 3 phases: G1, S and G2
95
What is the G1 phase of interphase?
Interruption in DNA duplication (doesn't happen). Cell metabolically active. Most of its organelles and cytosolic components, replication of centrosomes begins. All cell activities take place. Very short phase in cancer and embryonic cells. In cells that remain in G1 for a long time, it's called the G0 phase
96
What is the S phase of interphase?
Interval between G1 and G2. DNA replicates. About 8 hours. The 2 identical cells formed later during division will therefore have the exact same genetic material
97
What's the G2 phase of interphase?
About 4-6 hours. Cell growth continues. Enzymes and other proteins are synthesized in preparation for division. Replication of centrosomes is completed.
98
What is the mitotic phase?
Results in the formation of 2 identical cells. Consists of nuclear division (mitosis) and cytoplasmic divisio (cytokinesis)
99
What is mitosis?
Distribution of 2 sets of chromosomes into 2 separate nuclei... exact partitioning of genetic material. Divided into 4 stages: prophase, metaphase, anaphase and telophase
100
What is prophase?
Chromatin fibers condense and sorten into chromosomes that are visible under a light microscope. Each chromosome has a pair of identical strands called chromatids (due to S phase). Centromere holds the chromatid pair together. Outside f each centromere is a protein complex called kinetochore. Tubulins in pericentriolar material form the mitotic spindle (microtubules that attach to the kinetochore)... as microtubules lengthen they push the centrosomes to the poles of the cell so the spindle extends from pole to pole. Nucleolus disappears and nuclear envelope breaks down.
101
What is metaphase?
Microtubules of the mitotic spindle align the centromeres of the chromatid pairs at the exact centre of the mitotic spindle... this midpoint region is called the METAPHASE PLATE
102
What is anaphase?
Centromeres split, separating the 2 members of each chromatid pair which move toward opposite poles of the cell. Chromatids, when separate, are called chromosomes.
103
What is telophase?
Finale stage. After chromosomal movement stops. Identical sets of chromosomes uncoil and revert to the thread-like chromatin form. A nuclear envelope forms around each chromatin mass. Nucleoli reappear. Mitotic spindle breaks up.
104
What is cytoplasmic division (Cytokinesis)?
Happens after the mitotic phase. Division of a cell's cytoplasm and organelles into 2 identical cells. Begins in late anaphase with the formation of a cleavage furrow (slight indentation of plasma membrane)... complete in telophase. Actin microfilaments form a contractile ring that pulls the plasma membrane inwards. 2 sets of chromosomes end up in separate cells.
105
What are the 3 possible destinies of a cell?
1) To remain active and function without dividing. 2)To grow and divide. 3) To die
106
What is cyclin-dependent protein kinases (Cdk's)?
Enzymes that transfer a phosphate group from ATP to a protein to activate the protein. Other enzymes can remove the P group to deactivate it. This activation and deactivation of Cdk's at the appropriate time is crucial for the initiation and regulation of DNA replication, mitosis, ad cytokinesis. Cyclins are the proteins that turn Cdk's on and off
107
Why are levels of cyclin important?
Levels of cyclin in the cell are important for determining the sequence of events in cell division... towards the end of mitosis cyclin levels decline rapidly and mitosis ends
108
Describe the process of apoptosis
A triggering agent from either outside or inside the cell causes cell suicide genes to produce enzymes that damage the cell in several ways, including the disruption of its cytoskeleton and nucleus... DNA within the nucleus fragments and cytoplasm shrinks. Nearby phagocytes ingest dying cell
109
What is necrosis?
Death resulting from tissue injury. Many adjacent cells swell and burst and spill their cytoplasm into interstitial fluid... this debris initiates an inflammatory response from immune system
110
What is meiosis?
Reproductive cell division that occurs in gonads... produces gametes where the number of chromosomes is reduced by half (23) so they are haploid cells. Fertilisation restores the diploid number of chromosomes.
111
Describe prophase 1 of meiosis 1
Chromosomes shorten and thicken, the nuclear envelope and nucleoli disappear and mitotic spindles form. Two sister chromatids of each pair of homologous chromosomes pair off (SYNAPSIS). The resulting 4 chromatids form a TETRAD. Second, an exchange between parts of non sister (genetically different) chromatids occurs and is called CROSSING OVER (permits an exchange of genes between chromatids). Crossing over results in genetic recombination
112
Describe metaphase 1 of meiosis 1
The tetrads formed by the homologous pairs of chromosomes line up along the metaphase plate
113
Describe anaphase 1 of meiosis 1
Members of each homologous pair of chromosomes separates as they are pulled to opposite poles by microtubules attached to the centromeres. ... the paired chromatids held together by a centromere remain together.
114
Describe telophase 1 and cytokinesis of meiosis 1
Similar to mitosis.The NET EFFECT of meiosis 1 is that each resulting cell contains the haploid number of chromosomes.
115
Describe meiosis II
Four phases and are similar to mitosis: centromeres split and the sister chromatids separate and move toward opposite poles. 2 haploid cells divide resulting in 4 haploid cells. ... genetically different from original diploid cell
116
Why are RBCs a disc shape?
Gives it large SA to carry oxygen
117
Why are smooth muscle cells a long spindle shape>
It shortens as it contracts which allows smooth muscle cells to narrow/widen the passage of blood flowing through blood vessels... so they regulate blood flow through various tissues
118
Why do epithelial cells have microvilli?
Microvilli increases the SA, so cells that line the intestine the large SA area speeds the absorption of digested foods.
119
Why do nerve cells have long extensions?
Allows them to conduct nerve impulses over great distances
120
List some reasons for aging.
1) "aging genes": We are all born with them (theory) and they are part of our genetic blueprint. But they bring about aging by slowing down or halting processes vital to life. 2) Telomeres: Specific DNA sequences found at the tips of each chromosome that protects the chromosomes from erosion and sticking together. In most normal body cells each cycle of cell division shortens the telomeres and after many cycles they can be completely gone. 3) Glucose: Added to proteins inside and outside of cells forming irreversible cross links between adjacent protein molecules. With advanced aging more cross links form, which contributes to the stiffening and loss of elasticity that occur in aging tissues.
