AB2: Membranes, walls and organelles Flashcards
What are lipid rafts?
In places the lipid bilayer may be thicker than normal and come out into the extracellular space and contain a lot of proteins and cholesterol
What are transmembrane proteins? why are they difficult to study in biological membranes?
Comprise of one or more polypeptide chains winding back and forth across the lipid bilayer
They are difficult to study using x-ray crystallography as the lipid-protein complexes do not readily crystallise
What are the functions of the plasma membrane?
1) Impermeable to water and water-soluble molecules
2) Self-healing- gaps in the membrane rapidly reseal due to hydrophobic binding between phospholipid molecules
3) Signalling and transport- due to embedded proteins such as receptors and ion channels
4) Cell recognition
What is the difference between gram positive and gram negative bacteria?
Gram positive bacteria absorb the crystal violet dye and appear purple because outside of their membrane they have a thick peptidoglycan cell wall
Gram negative bacteria do not absorb the crystal violet dye and appear red because they have a double lipid bilayer- the inner lipid bilayer of the plasma membrane and outside that a lipid structure containing lipopolysaccharides and very little peptidoglycan
What is the capsule?
An additional thick polysaccharide layer secreted by some bacteria as an additional defensive layer against the immune response from mammals
What is the structure of the plant cell wall?
Made up of a primary cell wall made up of parallel aligned fibres (flexible- deposited during growth)- parallel fibres can stretch apart meaning the plant cell can grow.
As the cell matures a secondary cell wall is formed with non-aligned fibres (rigid- deposited once growth has stopped)
Middle lamellae between primary and secondary cell walls- sticky layer of polysaccharides (pectins) that hold adjacent cells together
What are the functions of the plant cell wall?
Inert barrier- regulates entry + exit of substances
Rigid secondary cell wall- maintains shape despite movement of water
Flexible primary cell wall- allow growth in early development of the plant
What is the structure of the extracellular matrix in animal cells?
A gel made up of glycoproteins, such as fibronectin (binds to integrin proteins in the membrane) and collagen (binds to fibronectin)
Also contains proteoglycans (also bind to fibronectin)
What is the function of the extracellular matrix in animal cells?
Forms a gel: provides mechanical protection in tissues.
Flexible so allows changes in shape and size.
Communication- integrins can transmit signals between ECM and the inside of the cell- signalling can influence gene expression so affects cell function + differentiation.
What is the structure if the nucleus?
- Membrane limited organelle
- Has an inner and outer membrane making up the nuclear envelope- evolved from involution of plasma membrane- double lipid bilayer separated by 20-40nm space
- Inside the nucleus there is the nucleolus where ribosomal RNAs are synthesised and the genetic material made of chromatin- complex comprising of DNA and histones
- In the nuclear envelope there are large protein pores embedded in the membrane allowing molecules to move in and out of the cell- inner membrane is lined by nuclear lamina which is coated by intermediate filaments (lamines)
What is the function of the nucleus
Contains most of the genes in eukaryotic cells- mitochondria and chloroplast also have their own DNA.
Chromosomes- each is a single DNA molecule with its associated histones.
Pore complex- controls entry and exit of protiens and RNA and macromolecules.
Nuclear lamina maintains shape of the nucleus.
Nucleolus synthesis of rRNA and assembly into ribosomal subunits- works in association with pore complexes
What is the structure of a chloroplast? What part of the structure of a chloroplast indicates the endosymbiosis theory?
Bound by a double biological membrane- an outer and an inner membrane with a space in between the two.
The space that’s surrounded by the inner membrane is the stroma- within the stroma are granum which are stacks of thylakoids which are the units containing chlorophyll.
The outer and inner membranes probably indicates evolution from endocytosed photosynthetic bacteria which colonised primordial eukaryotes (endosymbiosis)
What is the function of the chloroplasts?
1) Inter membrane space: composition controlled by solute transport to/from this space by transporter proteins in the inner membrane
2) Stroma: location of the light independent reactions
3) Thylakoid space: Where the Chlorophyll and light dependent reactions occur
What is the structure of the ribosome?
Found in the cytosol and rough endoplasmic reticulum
Made up of a large and a small subunit
Made up of a large number of proteins and ribosomal RNAs
What is the function of the Ribosome? how do eukaryotic and prokaryotic ribosomes differ?
Translates a mRNA nucleotide sequence into a protein amino acid sequence
1) Eukaryotic ribosomes (80S) are larger than in bacteria (70S)- archaea have similar ribosomes to eukaryotes
2) Eukaryotes and bacteria differ in their sensitivity to drugs- drugs that kill bacteria can work by binding to bacterial ribosomes but not human ribosomes eg streptomycin
