Chapter 3 Flashcards
(27 cards)
What is the plasma membrane
It’s a thin boundary made up of lipids(fats) that separates the intracellular and extracellular environments
It is selectively permeable, which means that only particular molecules can enter and exit the cell
All cells have a plasma membrane
What is the structure of plasma membrane
is a phospholipid bilayer embedded with proteins, carbohydrates and cholesterol
what is the structure of the phosphate heads
Made up of glycerol and a phosphate group
Negatively charged, making it hydrophilic (water loving) and polar
The 2 fatty acid chains are:
Made of long chains of carbon and hydrogen
Uncharged, hydrophobic (water fearing) and non-polar
Phosphate heads are hydrophilic so they are attracted to water, which is a polar substance
What type of molecules are phosphate heads
- Because phospholipids have both hydrophobic and hydrophilic parts, they are an amphipathic molecule
- This makes the plasma membrane stable: the fatty acid tails are repelled from the water whilst the phosphate heads are attracted to water, so a stable bilayer naturally forms
what is the fluid mosaic model
This model explains that:
Molecules that make up the membrane are not held static in one place
Many different types of molecules are embedded in the plasma membrane
The plasma membrane is ‘fluid’ because phospholipids continually move laterally (side to side) in the membrane
The ‘mosaic’ component of the model comes from the proteins and carbohydrates embedded in the membrane
Protein structures
Integral protein: proteins that are a permanent part of the membrane
Transmembrane protein: integral proteins that span the entire bilayer
Peripheral protein: are temporarily attached to the plasma membrane
Protein structures
Integral protein: proteins that are a permanent part of the membrane
Transmembrane protein: integral proteins that span the entire bilayer
Peripheral protein: are temporarily attached to the plasma membrane
Protein functions
Transport: channels or pumps that control what enters or exits the cell, making the plasma membrane selectively permeable
Catalysis: speeding up chemical reactions with the help of a protein called enzymes
Communication: Receive signals or recognise cells or molecules. Often attached the cytoskeleton to transmit signals into the cell
Adhesion: stick to other cells, the extracellular matrix, or the cytoskeleton
Carbohydrate structure
usually in chains that extend outside the cell, rooted in the membrane to lipids (glycolipids) or proteins (glycoproteins)
Carbohydrate purpose
aid with cell-cell communication, signaling recognition of self or non-self (foreign) molecules, and adhesion
Cholesterol structure
A lipid steroid that embeds itself between the fatty acid tails of the phospholipid bilayer in animal cells. Cholesterol is replaced with similar molecules in other kingdoms but all are functionally similar.
Cholesterol function
regulates the fluidity of the membrane. At higher temperatures, the cholesterol keeps phospholipids bound together. At lower temperatures, cholesterol disrupts the fatty acid tails stopping phospholipids from becoming a solid boundary.
What is osmosis
Is the diffusion of water across a selectively permeable membrane from areas of low solute concentration to areas of high solute concentration.
Water can move through the membrane as it is so small even though it is hydrophilic.
what are the 3 different types of tonicity in solute concentrations
Hypertonic- solutions have comparatively higher solute concentrations, so water moves into the hypertonic solution from adjacent areas with lower solute concentrations.
Isotonic- solutions have equal solute concentrations, so there is no net movement of water.
Hypotonic- solutions have comparatively lower solute concentrations, so water moves from a hypotonic solution into adjacent areas with a higher solute concentration
how does tonicity effect cells
Tonicity of a solution will affect cell size.
If a plant cell cytosol is hypotonic compared to extracellular fluid, water will move into the cell cause it to swell and become turgid.
It won’t burst due to the cell wall.
When water moves out of a plant cell (hypertonic) the cell shrinks and becomes plasmolysed
Animal cells placed in a hypotonic solution will increase in volume until they lyse. This is because they don’t have a cell wall.
what is lysing or lysis
Lyse or lysis is the breakdown of a cell caused by damage to its plasma membrane.
what is the biological importance of the effect of tonicity on cells
High turgor pressure keeps plants from wilting.
Turgor or the state of turgidity results in rigidity of cells or tissues, due to the absorption of fluid.
Saline solution in a hospital drip is isotonic to our cells- ensuring that your blood cells do not shrivel or lyse.
What is active transport and its two types
Active transport of substances across the membrane using protein pumps to move molecules against the concentration gradient.
It involves the use of energy (ATP)
There are two types
- Protein mediated transport
- Bulk transport
what is protein mediated transport
Cells must use energy and protein pumps to move the ions against the concentration gradient and into the cytoplasm
Adenosine triphosphate (ATP) ->-> Adenosine diphosphate (ADP) + energy + phosphate group
These situations require:
- energy in the form of adenosine triphosphate (ATP)
- Membrane proteins, typically protein pumps and carrier proteins
what are the three steps of protein mediated transport
- Binding- target molecule binds to the specific protein pump.
- Conformational change- one P from ATP cause a conformational change in the protein pump
- Release- target molecule is pushed through the protein and released to the other side of the membrane.
What is bulk transport and its two types
Is a type of active transport that moves large molecules of groups of molecules (amino acids, proteins, signalling molecule or pathogens) into or out of a cell using vesicles.
Endocytosis and exocytosis
What is endocytosis
“Enter”-brings substances into the cell
Involves transporting of groups of molecules into the cell
Many molecules that the cell requires to survive are too big to enter via protein channels
Once inside the cell these substances are broken down, used for metabolic processes or become structural elements of the cell
Can also be a defence mechanism- if a cell engulfs an invader or toxin a lysosome can fuse with the vesicle and digest it.
What are the 3 steps of endocytosis
- Fold- plasma membrane folds inwards to form a cavity that fills with extracellular fluid and the target molecule
- Trap- plasma membrane continues to fold back on itself until the 2 ends of a the membrane meet and fuse together
- Bud- vesicle (endosome) pinches off from the membrane. It can then be transported to the appropriate cellular location
What is exocytosis
“Exit” -sends substances out of the cell
Process that releases contents from a cell
Proteins are made by ribosomes located on the surface of the endoplasmic reticulum, sorted, packaged and modified at the Golgi apparatus and then transported in vesicles to the membrane for exocytosis
Important as cells often need to release products such as hormones neurotransmitters and antibodies in large amounts.
