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68 Cards in this Set
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Phospholipid bilayers |
Phospholipids form bilayers in water due to the amphipathic properties of phospholipid molecules |
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Hydrophilic |
Attracted to water |
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Hydrophobic |
are NOT attracted to water |
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Amphipathic |
Both hydrophilic and hydrophobic ex: Phospholipids |
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Phosphate Head |
-Hydrophilic -"Polar Head" -Face the water (act more like a solid) |
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Hydrocarbon Tail |
-Hydrophobic -"Non-Polar Tail" -Two Hydrocarbon tails -Face inwards (behave as a liquid) |
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Membrane Proteins are diverse in terms of : |
-structure -position in the membrane -function |
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Function of cell membrane: |
Forms a barrier through which ions and hydrophilic molecules cannot easily pass |
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Functions of membrane proteins: |
-Hormone Binding sites -Enzymatic action -Cell adhesion -Cell-to-cell communication -Channels for passive transport -Pumps for active transport |
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Integral Proteins |
-Have both Hydrophobic and Hydrophilic regions -Control the entry and removal of specific molecules from the cell -embedded in the hydrocarbon chains |
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Peripheral Proteins |
-Hydrophilic on their surface -Attached to the surface of integral proteins |
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The more active a membrane... |
The higher is its protein content |
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How much % protein is in chloroplasts and mitochondria? |
75% |
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Cholesterol |
-Allows an effective membrane function at a wider range of temperatures -Type of lipid (steroid) -Restricts molecular motion and fluidity of the membrane by reducing the permeability to hydrophilic particles. |
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Davson and Danielli 1930 |
"Sandwich model" -Layers of protein on both sides of the phospholipid bilayer |
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Singer and Nicolson 1966 |
"Fluid Mosaic Model" -Proteins occupy a variety of positions in the membrane and are free to move |
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Structure of membrane proteins: |
Proteins are very varied in size and globular in shape so it is unlike for them to form continuous layers |
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Freeze-etched electron micrographs |
The rapid freezing of cells and then fracturing them |
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Fluorescent antibody Tagging |
-proves that membrane proteins are free to move within the membrane -Red or green markers are attached to the antibodies which bind to the membrane proteins -the cells were fused and mixed throughout the membrane of the fused cell |
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3 things which falsified the Davson and Danielli model: |
-Freeze-etched electron micrographs -Fluorescent antibody tagging -Structure of membrane proteins |
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The fluidity of membranes allows... |
Materials to be taken into cells by endocytosis or released by exocytosis |
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Endocytosis |
-A process which allows larger molecules to enter the cell across the plasma membrane -uses energy from ATP (active transport) |
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Vesicles |
-Move materials within cells -Contain water and solutes from outside the cell - Often contain larger molecules |
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Exocytosis |
-A process which allows larger molecules to leave the cell across the plasma membrane |
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Simple Diffusion |
-One of the methods used when moving particles across membranes -The passive movement of molecules or particles along a concentration gradient or from regions of higher to regions of lower concentration |
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Diffusion |
The spreading out of particles in liquids and gases that happens because the particles are in continuous random motion |
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Passive Transport |
-Does not require energy -Movement down the concentration gradient |
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Facilitated diffusion |
-Particles can pass in or out of cells if there are channels for them -the process of spontaneous passive transport (as opposed to active transport) of molecules or ions across a biological membrane via specific transmembrane integral proteins. |
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Osmosis |
-Diffusion of water molecules -is the spontaneous net movement of solvent molecules through a semi-permeable membrane into a region of higher solute concentration, in the direction that tends to equalize the solute concentrations on the two sides. -HIGH to LOW |
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Active transport |
-ATP is required -movement of substances against the concentration gradient |
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Axon |
A part of a neuron (nerve cell) -Conveys messages rapidly from one part of the body to another in an electrical form (nerve impulse) |
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Sodium-Potassium Pump |
-The process of moving sodium and potassium ions across the membrane by the use of active transport |
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Facilitated Diffusion of Potassium in axon |
(see packet) |
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Solutes that are Osmotically active: |
-glucose -sodium ions -potassium ions -chloride ions |
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Osmolarity |
The osmolarity of a solution is the total concentration of osmotically active solutes Unit: -osmoles (Osm) or milliosmoles (mOsm) |
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What is the osmolarity of human tissue? |
300 mOsm |
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Isotonic Solution |
Has the SAME osmolarity as a tissue |
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Hypertonic Solution |
Has a HIGHER osmolarity than the tissue |
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Hypotonic Solution |
Has a LOWER osmolarity than the tissue |
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Plasmolysis |
Plant cells with their membranes pulled away from their cell walls |
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How to prevent osmosis in excised tissues and organs: |
-The tissues/organs must be bathed in a solution with the same osmolarity as the cytoplasm |
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Hypertonic, Hypotonic and Isotonic effect on osmosis in excised tissues/organs: |
Hypertonic- Water leaves the cell by osmosis cytoplasm shrinks Hypotonic- Cells take in water, swell up, may burst, cell ghosts may form Isotonic- Water molecules enter and leave the cell at the same rate, remains healthy |
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What is Isotonic sodium chloride solution? What is it used for? |
It is called "saline" with an osmolarity of about 300 mOsm -used to rinse wounds -a basis for eye drops -used for packing donor organs |
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The cell cycle |
The sequence of events between one cell division and the next |
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Interphase |
-First and Longest stage of the cell cycle A very active phase of the cell cycle with many processes occurring in the nucleus and cytoplasm |
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What metabolic reactions occur during interphase |
-cell respiration -DNA replication -protein synthesis |
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G1 G2 & S |
G1- growth of cell G2- growth and preparations for division phase S-(synthesis phase) replication of the DNA(chromosomes) *Increase the number of organelles *Condensation of chromatin to chromosome *microtubules formation |
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Mitosis |
Division of the nucleus into two genetically identical daughter nuclei |
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What happens during Mitosis? |
During Mitosis one of these chromatids passes daughter nuclei to each other (Chromatid is a single DNA molecule) |
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Supercoiling of Chromosomes |
Supercoiling: -occurs during prophase -Condensation of chromosomes -repeatedly coiling the DNA molecule |
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The role of mitosis |
Mitosis is involved in: -asexual reproduction -growth -development of embryos -tissue repair |
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What are the 4 phases of mitosis? |
-prophase -metaphase -anaphase -telophase |
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Mitosis PROPHASE |
The chromatin fibres become more tightly coiled to form chromosomes **** |
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METAPHASE |
The chromosomes are moved to the middle of the cell-Metaphase plate ***** |
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ANAPHASE |
The two sister chromatids of each chromosomes are split=chromosomes ***** |
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TELOPHASE |
The chromosomes are at each pole |
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What is the mitotic index? |
ratio between the number of cells in mitosis in a tissue and the total number of observed cells |
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When does Cytokinesis occur? |
Cytokinesis occurs after mitosis and is different in animal and plant cells It usually begins before mitosis has been completed |
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What is cytokinesis? |
It is a process in which the cytoplasm of a single eukaryotic cell is divided to form two daughter cells |
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Cytokinesis in plant cells- |
-vesicles are moved to the equator - they fuse to form tubular structures -pectins and other substances are deposited between the two new membranes -middle lamella is formed that links the new cell walls -cells bring cellulose to the equator -cell wall is formed |
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what are Cyclins |
-proteins -control the cell cycle -ensure that cells divide when new cells are needed |
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How do cyclins work? |
-bind to enzyme -kinases (active) attach phosphate groups to other proteins in the cell - proteins are active -proteins carry out tasks specific to one of the phases of the cell cycle |
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Discovery of cyclins |
-Tim Hunt research in control of protein synthesis in sea urchin eggs discovered a protein that increased in concentration after fertilization then decreased in concentration |
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Tumours |
They are caused by uncontrolled cell division They can occur in any tissue or organ of both plants and animals |
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Benign |
-the cells adhere to each other dont envade nearby tissues of move to other parts of the body unlikely to cause much harm |
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Malignant
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cells can become detached and move elsewhere on the body to develop into secondary tumors are very likely to be life-threatining commonly known as cancer |
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What is the cause of malignant tumors? |
-carcinogens -mutations -mutagens -oncogenes -metasis |
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What are the 3 phases of interphase? |
G1, G2, S |