Cell structure and functions Part 2 Flashcards
1
Q
Plant Cell walls
A
- A protective layer external to and thicker than plasma membrane
- Composed of microfibrils of cellulose secreted to extracellular space
- Become embedded in matrix of other polysaccharides and proteins
Functions:
- Protects and maintains shapes of cell
- Prevents excessive water uptake
- Holds plant up against gravity
2
Q
Microfibrils
A
Long strings of cellulose bonded together by hydrogen bonds
3
Q
Extracellular Matrix (ECM)
A
- Made of glycoproteins and other carbohydrate-containing molecules secreted by cells
- What connects cells to the membrane
- Very important to keep human structure
- Most abundant: collagen
- Collagen fibres are embedded in proteoglycan network
- Some cells are attached by firbonectin ( a glycoprotein)
4
Q
Proteoglycan
A
Small core protein with any carbohydrate chains attached
- Complexes form when many proteoglycans attach to one long polysaccharide molecule
5
Q
Fibronectin
A
A ECM protein that binds to cell surface receptor proteins called integrins
6
Q
Integrins
A
- Built into ans span plasma membrane
Functions:
- Bind microfilaments inside cell
- Bind ECM outside cell
- Transmit signals between ECM and cytoskeleton
7
Q
Cell junctions
A
Cells need to adhere, interact and communicate with each other
8
Q
Plasmodesmata
A
- Perforations in plant cell walls, lined by plasma membrane
- Channels connect cells so cytosol can pass through; this connection unifies most plants
- Little holes within the cell walls to help the transmission and exchange of small nutrients between the cells
9
Q
Main types of cell junctions
A
- Tight junctions
- Desmosomes
- Gap junctions
*Common in epithelial tissue that lines the outside or inside of body like ski, inside skin of mouth, external stomach tissue)
10
Q
Tight junctions
A
- Form continuous seals around the cells
- Proteins make a tight seal to prevent the passage of water both in and out of cell
- Present in stomach to keep acid in stomach; also present in skin
Functions: - Prevent leakage of extracellular fluid across layer of epithelial cells
- Prevent water of coming into cell
- Stops our body from constantly losing water
11
Q
Desmosomes
A
- Have long intermediate filaments that hold the cell together and is hard to pull apart
Functions:
- Function like rivets
- Fasten cells together into strong sheets
12
Q
Gap junctions
A
- Provide cytoplasmic channels between cells
- Similar to plasmodesmata
- Ions and small molecules can through
- Ions have a hard time passing through from other places because plasma membrane is mostly hydrophobic
13
Q
Plasma membrane
A
- 8nm thick
- Controls traffic in and out of cell
- Exhibits selective permeability (picky about what it lets in and out of cell)
Structure:
- Phospholipds
- Fluid mosaic model
14
Q
Phospholipids
A
- Most abundant lipids in most membrane
- Ability to form membranes is inherent in their structure
- Amphipathic (Both hydrophilic and hydrophobic –> hydrophilic head and hydrophibic tail)
- Phospholipid bilayer
15
Q
Fluid mosaic model
A
- Currently accepted model of what plasma membrane is like in animal cells
- Membrane is a mosaic of protein molecules drifting laterally in a fluid bilayer of phospholipids
- they are constantly moving around because the bond is not very strong, only together because fatty acid tails want to avoid water
16
Q
Membrane fluidity
A
- Membranes are not static (Fluid mosaic model)
- Some membrane proteins move, others do not
- Affected by temperature –> if temperature decreases, phospholipids become packed together and membranes solidifies
- Membrane with unsaturated hydrocarbon tails will remain fluid in lower temperature because kinds in tails prevent it from packing too closely
- Presence of cholesterol )a steroid)
