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Cell Dynamics > Cell Membrane & Endomembrane System > Flashcards

Cell Membrane & Endomembrane System Flashcards

1
Q

Functions of the Cell Membrane

A

Transport processes
Protective barrier/boundary
Cell-cell communication
Cellular signalling
Signal conduction
Cell to cell recognition
Cell shape

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2
Q

Protective barrier/boundary

A
  • Membranes define boundaries of cells and the boundaries of compartments (organelles).
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3
Q

Cell-cell communication

A
  • Specific plasma membrane gap junction proteins (desmosomes, tight junctions) of adjacent cells lines up and form pipelines between the two cells.
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4
Q

Transport processes

A
  • Membranes control what information is received from other cells or external environment.
  • Membranes control the import and export of signals from other cells or the external environment.
  • Membranes are flexible and have a capacity for movement and expansion.
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5
Q

Cellular signalling

A
  • Membrane proteins serve as receptors that recognise and bind specific molecules in the extracellular environment. This triggers a series of molecular events in the cell which can lead to a cellular response e.g. hormones.
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6
Q

Signal conduction

A
  • Membranes have electrical properties which can serve as a mechanism of signal conduction when a cell receives an electrical, chemical or mechanical stimulus, e.g. Neurons and muscle cells.
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7
Q

Cell to cell recognition

A
  • Some glycoproteins in the plasma membrane act as identification tags that are specifically recognised by membrane proteins to other cells.
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8
Q

Cell shape

A
  • Cytoskeletal may be noncovalently bound to membrane proteins, a function that helps maintain cell shape and stabilises the location of certain membrane proteins.
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9
Q

Fluid-Mosaic Model- FLUID

A

individual phospholipids and proteins can move side- to-side within the layer, like it’s a liquid.

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10
Q

Fluid-Mosaic Model- MOSAIC

A

the pattern produced by the scattered protein molecules when the membrane is viewed from above.

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11
Q

Lipid bilayer

A

2 layers of phospholipids.

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12
Q

Hydrophilic

A

molecules do not pass through easily.

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13
Q

Hydrophobic

A

molecules pass through easily.

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14
Q

The semi-permeable membrane

A
  • Substances that are soluble in lipids pass through easily.
  • Small molecules and larger hydrophobic molecules move through the membrane easily, e.g. O2, CO2, H2O.
  • Ions, hydrophilic molecules larger than water, and large molecules such as proteins do not move through the membrane on their own.
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15
Q

Structural components- LIPIDS

A
  1. Phospholipids (75%)
  2. Cholesterol (20%)
  3. Glycolipids (5%)
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16
Q

Structural components- PROTEINS

A
  1. Integral (involved in cell transport)
  2. Peripheral
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17
Q

Phospholipids

A
  • Individual units that make up the membrane.
  • Phospholipid has a head and a tail:
    * Head = hydrophilic phosphate
    group.
    * Tail = 2 hydrophobic strings of
    carbon and hydrogen atoms.
  • Watery fluids are found both inside a cell (intracellular fluid) and outside a cell (extracellular fluid).
  • The hydrophobic tails of membrane phospholipids are organised in a manner that keeps them away from water.
    Phospholipids are ‘amphiphatic’- Exhibit both hydrophilic and hydrophobic properties.
18
Q

CELL HOMEOSTASIS

A

The membrane maintains the internal equilibrium of the cell by controlling entry to and exit from the cell.

19
Q

Movement of phospholipids

A
  • Phospholipids can move sideways/laterally (approx 10 to the power of 7 times per second)
  • Phospholipids can flip flop across membrane (approx once a month)
20
Q

Cholesterol

A
  • Cholesterol is an amphiphatic molecule with a polar head which attaches to the polar part of phospholipids and its function is to stiffen the plasma membrane.
  • Cholesterol molecules are made up of four rings of hydrogen and carbon atoms.
  • They strengthen the membrane by preventing some small molecules from crossing it.
  • Cholesterol molecules also prevent the phospholipid tails from coming into contact and solidifying.
  • This ensures that the cell membrane stays fluid and flexible.
21
Q

Glycolipids

A
  • Glycolipids are molecules which have a fatty acid tail and a carbohydrate head (chains of sugars) and their function is in cell to cell recognition and communication.
  • Short carbohydrate chain covalently attached and this is exposed on the outer surface of the cell.
  • They provide stability for the cell and help cells join to other cells to form tissues.
  • Glycolipids play in humans is their contribution to blood type.
  • There are four main blood types: A, B, AB and O, and this variation stems from the different glycolipids present on the surface of red blood cells (erythrocytes).
22
Q

Integral proteins

A
  • These proteins have one or more hydrophobic regions with an affinity for the hydrophobic interior of the lipid bilayer.
  • These proteins are embedded in the membrane and cannot be easily removed.
  • Generally transport proteins:
    * Channel proteins
    * Carrier proteins
23
Q

Peripheral proteins

A
  • These proteins lack hydrophobic sequences and therefore do not penetrate the lipid bilayer.
  • Instead they associate with the membrane surfaces and through weak electrostatic forces.
  • They bind either to the polar heads of the membrane lipids or the hydrophilic portions of the integral proteins that extend out of the membrane.
24
Q

2 Classes of transport proteins

A
  1. Carrier Proteins: bind solute on one side of membrane, deliver it to other side by conformational change in protein (turnstile).
  2. Channel Proteins (Ion Channels): form hydrophilic pores in membrane through which solutes (mainly ions) can diffuse (trapdoor).
25
Q

Cell membrane transport

A

Transport across the lipid bilayer of the cell membrane can be divided into two distinct types depending on the energy requirement of the process:
(a) Passive transport
(b) Active transport

26
Q

Passive Transport

A

DOES NOT require energy. It occurs
because of the tendency for dissolved molecules to move or diffuse from higher to lower concentrations.
* Passive transport can be divided into two types:
* Simple diffusion
* Facilitated diffusion

27
Q

Simple Diffusion

A

whereby molecules move from a region of higher concentration to a region of lower concentration.

28
Q

Facilitated Diffusion

A

whereby molecules depend on specialised membrane proteins to aid the passage of ions or polar molecules across the hydrophobic interior of the membrane.

29
Q

Active Transport

A

DOES require the input of energy.
* Active transport moves solutes against their concentration gradient which require work.
* Therefore this type of transport requires special membrane proteins that are often referred to as pumps. Because of the energy input, active transport can result in the generation of a concentration gradient across the membrane.
* Examples: Sodium-potassium pump which exchange sodium
(Na+) out of the cell for potassium (K+) inside the cell.

30
Q

Active Coupled transport

A

ATP-powered pump that transports a specific solute can indirectly drive the active transport of several other solutes across the membrane.

30
Q

Two types of co-transport

A
  • Symport coupled transport- molecules move in the same direction across the membrane.
    E.g. Glucose and sodium from outside to inside the cell.
  • Antiport coupled transport– molecules move in opposite directions across the membrane.
    E.g. Sodium potassium pump to pump sodium outside the cell and pump potassium into the cell.
31
Q

ENDOMEMBRANE SYSTEM

A

The organelles that are “connected” (tangibly or via transport) together by phospholipid membranes.

32
Q

Endomembrane System- Function

A
  • Membranes provide compartmentalisation, which allows different places in the cell to have different environments.
  • With this arrangement, the cell can “build” in some areas, “break down” in others, and reserve other areas for storage or other functions.
  • Nuclear membranes (envelope), the endoplasmic reticulum, the Golgi apparatus, lysosomes, vesicles, endosomes and the cell membrane.
33
Q

Rough Endoplasmic Reticulum

A

synthesizes proteins and packages them in vesicles commonly go to Golgi apparatus

34
Q

Smooth Endoplasmic Reticulum

A

synthesizes lipids and also performs various other functions

35
Q

Transport Vesicles

A

shuttle proteins and lipids to various locations such as the Golgi apparatus

36
Q

Golgi Apparatus

A

modifies proteins and lipids from the ER; sorts them and packages them in vesicles

37
Q

Lysosome

A

contains digestive enzymes that breakdown worn-out cell parts or substances entering the cell at the plasma membrane

38
Q

Secretory Vesicles

A

fuse with the plasma membrane as secretion occurs

39
Q

Incoming Vesicles

A

brings substances into the cell that are digested when vesicle fuses with a lysosome.

Cell Dynamics (4 decks)

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