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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

Hydrophilic

Attracted to water

Hydrophobic

are NOT attracted to water

Amphipathic

Both hydrophilic and hydrophobic


ex: Phospholipids

Phosphate Head

-Hydrophilic


-"Polar Head"


-Face the water (act more like a solid)

Hydrocarbon Tail

-Hydrophobic


-"Non-Polar Tail"


-Two Hydrocarbon tails


-Face inwards (behave as a liquid)

Membrane Proteins are diverse in terms of :

-structure


-position in the membrane


-function

Function of cell membrane:



Forms a barrier through which ions and hydrophilic molecules cannot easily pass

Functions of membrane proteins:

-Hormone Binding sites


-Enzymatic action


-Cell adhesion


-Cell-to-cell communication


-Channels for passive transport


-Pumps for active transport

Integral Proteins

-Have both Hydrophobic and Hydrophilic regions


-Control the entry and removal of specific molecules from the cell


-embedded in the hydrocarbon chains



Peripheral Proteins

-Hydrophilic on their surface


-Attached to the surface of integral proteins

The more active a membrane...

The higher is its protein content

How much % protein is in chloroplasts and mitochondria?

75%

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.

Davson and Danielli 1930

"Sandwich model"


-Layers of protein on both sides of the phospholipid bilayer

Singer and Nicolson 1966

"Fluid Mosaic Model"


-Proteins occupy a variety of positions in the membrane and are free to move



Structure of membrane proteins:

Proteins are very varied in size and globular in shape so it is unlike for them to form continuous layers

Freeze-etched electron micrographs

The rapid freezing of cells and then fracturing them



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

3 things which falsified the Davson and Danielli model:

-Freeze-etched electron micrographs


-Fluorescent antibody tagging


-Structure of membrane proteins

The fluidity of membranes allows...

Materials to be taken into cells by endocytosis or released by exocytosis

Endocytosis

-A process which allows larger molecules to enter the cell across the plasma membrane


-uses energy from ATP (active transport)



Vesicles

-Move materials within cells


-Contain water and solutes from outside the cell


- Often contain larger molecules

Exocytosis

-A process which allows larger molecules to leave the cell across the plasma membrane



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

Diffusion

The spreading out of particles in liquids and gases that happens because the particles are in continuous random motion

Passive Transport

-Does not require energy


-Movement down the concentration gradient

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.

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

Active transport

-ATP is required


-movement of substances against the concentration gradient

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)

Sodium-Potassium Pump

-The process of moving sodium and potassium ions across the membrane by the use of active transport

Facilitated Diffusion of Potassium in axon

(see packet)

Solutes that are Osmotically active:

-glucose


-sodium ions


-potassium ions


-chloride ions

Osmolarity

The osmolarity of a solution is the total concentration of osmotically active solutes


Unit:


-osmoles (Osm) or milliosmoles (mOsm)

What is the osmolarity of human tissue?

300 mOsm

Isotonic Solution

Has the SAME osmolarity as a tissue

Hypertonic Solution

Has a HIGHER osmolarity than the tissue

Hypotonic Solution

Has a LOWER osmolarity than the tissue

Plasmolysis

Plant cells with their membranes pulled away from their cell walls

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



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



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

The cell cycle

The sequence of events between one cell division and the next

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

What metabolic reactions occur during interphase

-cell respiration


-DNA replication


-protein synthesis

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

Mitosis

Division of the nucleus into two genetically identical daughter nuclei


What happens during Mitosis?

During Mitosis one of these chromatids passes daughter nuclei to each other


(Chromatid is a single DNA molecule)

Supercoiling of Chromosomes

Supercoiling:


-occurs during prophase


-Condensation of chromosomes


-repeatedly coiling the DNA molecule



The role of mitosis

Mitosis is involved in:


-asexual reproduction


-growth


-development of embryos


-tissue repair



What are the 4 phases of mitosis?

-prophase


-metaphase


-anaphase


-telophase

Mitosis PROPHASE

The chromatin fibres become more tightly coiled to form chromosomes


****

METAPHASE

The chromosomes are moved to the middle of the cell-Metaphase plate


*****

ANAPHASE

The two sister chromatids of each chromosomes are split=chromosomes


*****



TELOPHASE

The chromosomes are at each pole



What is the mitotic index?

ratio between the number of cells in mitosis in a tissue and the total number of observed cells

When does Cytokinesis occur?

Cytokinesis occurs after mitosis and is different in animal and plant cells


It usually begins before mitosis has been completed

What is cytokinesis?

It is a process in which the cytoplasm of a single eukaryotic cell is divided to form two daughter cells



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

what are Cyclins

-proteins


-control the cell cycle


-ensure that cells divide when new cells are needed

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



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



Tumours

They are caused by uncontrolled cell division


They can occur in any tissue or organ of both plants and animals

Benign

-the cells adhere to each other


dont envade nearby tissues of move to other parts of the body


unlikely to cause much harm

Malignant

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



What is the cause of malignant tumors?

-carcinogens


-mutations


-mutagens


-oncogenes


-metasis



What are the 3 phases of interphase?

G1, G2, S