Lesson 2A - Cell Membrane Flashcards
It is referred as the gateway to the cell.
Cell Membrane
It:
1. Acts as a boundary
2. controls what enters and leaves cell
3. Regulates chemical composition
4. Maintains homeostasis
Cell Membrane
What property does the cell membrane have that allows UNICELLULAR organism to move?
Flexible
It provided the first evidence that biological membrane consist of lipid bilayers.
Studies of the red blood cell plasma
Fill in the blanks:
The cell membrane is _________ and allows a _________ _________ to move
flexible, unicellular organism
What did the red blood cell plasma studies proved about biological membranes?
Provided first evidence that the biological membranes were consisted of lipid bilayers.
The three Plasma Membrane Models:
- Sandwich Model
- Unit Membrane Model
- The Fluid Mosaic Model
It was proposed by Danielli and Davson, a model where they believe that the cell membrane is made up of two globular proteins with phospholipid inside to make a layer and then join two layers together to make a channel for molecules to pass.
Sandwich Model (Danielli-Davson Model)
It was proposed by Robertson. where it was a more refined version of the Sandwich Model.
It theoried that the outer layer of protein has a phospholipid bilayer inside.
All cells were of the same composition.
However, can’t explain how molecules pass through the use of proteins with non polar parts.
Unit Membrane Model (Robertson Model)
Proposed by Singer and Nicholson, described as the presence of Phospholipid bilayer with proteins either partially or fully embedded.
Electron micrographs or freeze-fractured membrane is also evident.
The Fluid Mosaic Model
Among the three membrane model, which is the most correct?
The Fluid Mosaic Model
Among the three models, what four reason made the Fluid Mosaic Model the correct one?
1) Rapidly freeze specimen
2) Use special knife to cut membrane in half
3) Apply a carbon + platinum coating to the surface
4) Use scanning electron microscope to see the surfac
It is the basic paradigm of biological
membrane structure
The Fluid Mosaic Model
How were the lipids in a membrane organized?
Liquid Crystalline Lattice
What happens to the liquid crystalline lattice organization of the lipids in the membrane once it reaches the transition temperature?
becomes a frozen crystalline gel
Why is it that plasma membrane is composed of two layers of lipids?
It means that atleast a portion of the membrane repels the water that constantly surrounds it.
This evades the possibility of the allowing of too much water in the cell which may cause the cell to burst.
Why is the Fluid Mosaic Model attributed as “Fluid”?
Due to its consistency (olive oil) at body temperature, due to unsaturated phospholipids.
Phospholipids and proteins move around freely within the layer, like liquid.
What moves freely within the cell membrane like liquid?
Phospholipids and Proteins
What is the consistency of plasma membrane being compared to at body temperature?
Olive Oil
What makes the Fluid Mosaic Model affiliated with the term “Mosaic”?
The presence of different types of proteins (50 types) that forms a collage at either side of the membrane and from cell to cell.
What part of the membrane is Hydrophilic, facing out?
Heads
What part is Hydrophobic, facing in?
Tails
What produces the mosaic pattern of the Fluid Mosaic Model?
Scattered protein molecules when membrane is viewed from above.
What happens to the hydrocarbons/ phospholipids at low temperatures?
They go tightly packed
What happens to the hydrocarbon/phospholipid at high temperatures?
They move to fluid phase, allowing movement.
How do cell membrane repairs itself when it suffers small tears in membrane?
Through small vesicles that were spontaneously formed.
It is energetically favorable in the contect of vesicle formation.
Formation of sphere.
Fill in the Blanks:
________ is a harsh ionic detergent and _______, a gentler non-ionic detergent, are commonly used solubilizing agents.
SDS, Triton X-100
What scheme should be followed in studying membrane protein?
- Solubilization,
- Purification, and
- Reconstitution in Liposomes
They can be solubilized by detergents that disrupt the membrane?
Membrane Proteins
Two types of phospholipid movements?
- Lateral Movement
- Flip-flop
A rare kind of phospholipid movement?
Flip-flop movement
A common movement by the lipids and some proteins?
Laterally to either side (Lateral Movement)
They are not fixed
in position but constantly moving in the cell membrane.
Proteins and Lipids
Proteins move how?
Laterally within the Cell Membrane - Lateral Diffusion
The lipids can move in what way?
Both laterally and rotate 360
degrees – flip-flop diffusion
It is another substance found in the lipid bilayer, the cell membrane, acting as regulator and affects fluidity.
Cholesterol
How does cholesterol affects fluidity in body temperatures (high temperature)?
It lessens fluidity by restraining the movement of phospholipids; also to reduce permeability to small molecules.
How does cholesterol affects fluidity in colder temperatures (low temperatures)?
It maintains fluidity by not allowing phospholipids to pack close together.
What does the cholesterol’s Planar Rings do in cell membrane?
More Rigid, Less Permeable, and Resistant to Low Temperature Crystalization.
It is a major component in animal cells.
Cholesterol
To which is cholesterol not found?P
Plant Membranes
It also functions the same as cholesterols.
Sterols
It posses similar molar amounts with?
Phospholipids
Three Classifications of Membrane Proteins:
- Peripheral Membrane Proteins
- Integral Membrane Proteins
- Transmembrane Proteins
These are proteins that dissociate
from the membrane following
treatments with polar reagents that do not disrupt the phospholipid bilayer. Seen on surface level, can be removed easily without damage.
Peripheral membrane proteins
It can be released only by
treatments that disrupt the
phospholipid bilayer. They pass through (embedded in) the cell membrane, removing it needs to be with the tearing up of the membrane.
Integral Membrane Proteins
It spans the lipid bilayer with
portions exposed on both
sides of the membrane. It goes all throughout the membrane and its parts are sticking out at the both sides of the cell membrane.
Transmembrane Proteins
What are the five types of Membrane Proteins?
- Transport Proteins
- Receptor Proteins
- Enzymatic Proteins
- Cell and Recognition Proteins
- Attachment Proteins
- Intercellular Junctions Proteins.
These are channel for lipid
insoluble molecules
and ions to pass freely
through. (Free Passing)
Channel Proteins
Bind to a substance and
carry it across
membrane, change
shape in process. (Carry it Across)
Carrier Proteins
Bind to chemical messengers (Ex.
hormones) which sends a message into the cell causing cellular reaction (Sends message to the cell)
Receptor Proteins
Carry out enzymatic reactions right at the membrane when a substrate binds to the active site. (Hastens the Chemical Reaction Process)
Enzymatic Proteins
In Cell Recognition Proteins, it acts as ID tags in extracellular surfaces.
Glycoproteins (and glycolipids)
Short branched chains of less than 15 sugars?
Carbohydrates
Important in ID tagging, which specifies species, cell type, individual. Crucial to determine body cells from foreign cells.
Cell Recognition Proteins
It is where the attachement happens to ensure and maintain cell shape and stabilize proteins.
Cytoskeleton
It is whre the protein Fibers and carbohydrates are seen that were secreted by cells and fills the spaces between cells and supports cells in a tissue.
It can also influence activity inside the cell and coordinate the behavior of cells in the tissue.
Extracellular Matrix
It bind cells together through tight junctions and gap junction
Intercellular Junction Proteins
Three Types of Cell Junctions
- Tight Junctions
- Desmosomes
- Gap Junctions
It is a junction type wherein transmembrane Proteins of opposite cells attach in a tight zipper-like fashion
Ensures no leakage
Ex. Intestine, Kidneys, Epithelium of skin
Tight Junction
It is a junction type where cytoplasmic plaques of two cells bind with the aid of
intermediate filaments of keratin. It also allows for stretching.
Ex. Stomach, Bladder, Heart
Desmosomes
It is a junction type wherein channel proteins of opposite cells join together providing channels for ions, sugars, amino acids, and other small
molecules to pass. It also allows communication between cells.
Ex. Heart muscle, animal embryo
Gap Junctions
They are substances that are not fixed nor in placed, it can float in membrane.
However, some of them are anchored to provide structional support, and perform specific fuctions.
This limitation is the reason why not all of the membrane _____ have this freedom of motion.
Proteins
