cells key organelles and features Flashcards
why do we need a lipid bi layer
to make a cell
some minerals
catalyse the formation of fatty acids from hydrogen and carbon monoxide
what are fatty acids made from
hydrogen and carbon monoxide
micelles
where polar fatty acids have self organise into circular formations where fatty acid tails point inward
why do micelles look the way they do
in water hydrophobic chains of fatty acid molecule turn towards each other –> thereby exposing the hydrophilic head
vesicles are spontaneously formed from
micelles
- requires acidic pH
- vesicles grow by fusion with micelles
what can trigger vesicle formation
clay surfaces
lipids in vesicle membranes are
dynamic –>flipping of lips can transport molecules over the membrane –> in this molecules can accumulate within the vesicle e.g. ribozymes
protocell
combining RNA replicase and vesicles
formation a protocell
- -> the RNA replicase used ribonucleotides to make a copy of another RNA replicase
- -> micelles fuse with he vesicle and enlarge it until it becomes unstable and divided
- -> random mistake could form better replicase and uptake of new RNA could incorporate new ribosomes, which could make the protocol grow and divide faster
- -> protocols compete for resources (fatty acids, ribonucleotides) and faster growing protocols are more competitive
faster growing protocols are more competitive
evolution
what are present in plasma membrane
specific proteins, lipids and sugars
plasma membrane
surround the cell and keeps contents inside whilst allowing transfer or info
the plasma membrane is made up of
two layers of fatty acid and head, tails on the inside and in the presence of water will assemble into a lipid bilayer
amphiphatic
have both hydrophilic and hydrophobic parts e.g. lipid bilayer
the plasma membraneeis
fluid
what can be used to demonstrate the fluidity of the plasma membrane
laser tweezers to pull the plasma membrane of a neuronal cell
what can effect membrane fluidity
steroids
cholesterol and the plasma membrane
reduces membrane fluidity at moderate temperatures and avoids solidification at low temperatures (temp buffer)
what is cholesterol involved in
the formation of vic D and estradiol and testosterone
how may an organelles be identified
by their lipid composition
lipid rafts
specialised lipid-protein regions found in membranes. Regions which assemble specialised lipids and proteins to perform a certain task e.g. sites of uptake in the plasma membrane are rich in cholesterol and sphingolipids and receptors
bio membranes are..
SEMI-PERMEABLE if molecules are uncharged and hydrophobic
charged molecules cannot
pass the bio-membrane e.g. sugars, ATP, proteins
highly hydrophilic molecules and ions
must go through transporters–> still diffusion and not driven by ATP e.g. facilitated glucose transport (allows glucose to flow in one direction)
energy consuming active transport uses
ATP to open channels to allow molecules to flow into the cell
membrane passage of polar proteins or ions requires
protein channels
–> atp driven transporters e.g. proton pumps- energy consuming active transport
how can sucrose diffuse into the the cell via
proton pumps can be linked to coo transporters, due to the proton gradient produced by the proton pump–> indirect ATP dependency
channels will close and open depending on
diff concentration in the inside outside of the cell
permeability of in channels is controlled by
gates in response to stimuli
types of channels
voltage gates, mechanically gated, temp gated, ligand gated
cells in the epithelium establish
tight and lateral and basal contact
gap junction
a field connecting channels each made of connexions, channels allow passage of ion and small molecules (1-2nm); supports exchange between the cytoplasm of adjacent cells
tight junction
function as a diffusion barrier, holds cell together- BB, consists of plasma membrane proteins (claudin,occulidin) that interact
which proteins are present in tight junctions
claudin and occuldin
adherens jucntion
consists of cadherin and catenin, cadherin bridge between ells, catenins link to the cytoskeleton
adhere junctions seem to be involved in
controlling actin organisation in epithelial cells
desomosome
contains specialised catherin proteins that interact with each other and with intermediate filaments (cytoskeleton)
–> resists shear force in epithelial and in muscle
extracellular matrix
fibres of secreted proteins (collagen, matrix proteins, glycoproteins). Holds tissues together and provides strength directing cell migration etc
tight junction
diffusion barrier, tissue integrity
adherens junction
organisation of actin
-cadherin and other proteins
gap junction
exchange between adjacent cells- connexins
desomosomes
resistance to shear forces
- cadherin and the proteins and intermediate filaments
- lateral
hemi-desomsomes
-connection to extracellular matrix –>basal
hemi-desomosomes more detail
contain many proteins, including integrins (protein) that interact with the extraceullar matrix
- found in epithelial cells
- anchor the epithelial cells to basal lamina -_> involved in signalling.
- only one-link intermediate filaments to extracellular matrix
ribosomes
consists of 2 subunits
can be 70s and 80s and proteins . ribosomes in the cytoplasm are attached to membranes and translate info from mRNA into proteins –> translation
the c70s ribsoomes
34 proteins in large subunit and 21 proteins in small subunit
80s ribosomes
49proteins in large subunit and 33 proteins in small unit
svedberg unit (S)
described sedimentation behaviour of particles (ribose)
- he developed a technique of analytical ultracentrifugation and seperated pure proteins from each other..
- particle mass, density and shape will determine s value
the cytoplasm is
crowded and diffusion is restricted e.g. larger objects almost don’t diffuse int the cell
the cytoplasm is made up of
300MG/ML PROTEINS AND RNA, MANY RIBOSOMES
Particles and molecules undergo random
brownian motion temp dependent –> movement is random
diffusion depends on
the size of the molecule –> the smaller the molecule the more it can move e.g. sugar molecule will more than a protein
how are molecules moved
by water
70s
50s and 30s
80s
60s and 40s
the nucleus
is the largest organelle in the cell, usually just 1, where mitosis occurs- known as the library of the cell
size of nucleus
2-10um (10% of cell volume)
what do nucleolus’ found in the nucleus form
ribosomes
- -> granular component
- -> ribosome assembly site
- fibrillar centre- rRNA transcription.
ribosomal proteins are imported into the
nucleolus
assembled ribosomes produced in the nucleolus are
exported into the cytoplasm
nucelar pores are found in the
nuclear envelope
nuclear pores are
Gates for transport in and out of the nucleus: highly ordered multi-protein complexes, which have eight fold symmetry. Numerous proteins build the pore and control nuclear export
how many diff nucleoprins in a pore
30
nuclear transport depends on
small GTPas and soluble import//export receptors
why are nuclear pores so evenly spaced
if a nuclear pores were clustered, this would not support an efficient transport method in or out of the nuclear
what prevent nuclear pores from clustering
lamina
lamina
found on the inside of the nuclear envelope made up of fibres keep the pores evenly space.
how can lamina importance be established
by using dna technology genes can be turned off to show how important they are when it comes to dispersion of pores
what forms intermediate filaments of the nuclear lamina
several lamins
how is the nuclear membrane broken down
lamina are phosphorylated
how is the nuclear envelope reformed at the end of mitosis
dephosphorylation of lamins. then the nuclear envelope fragments are fused
lamina and phosphorylation
When the Lamins are phosphorylated it causes the nuclear envelope to disassemble and for chromosome to condense. The dephosphorisation of the Lamins occurs and the nuclear envelope starts to reform. Then nuclear envelope fragments will fuse.
what helps visualise the nucleus and its interaction with the ER
GFP is joined to the nucleus and the GFP is attached to the endoplasmic reticulum helps visualise the interaction between the ER and the nucleus within a living cell.
during mitosis the ncleus
releases its content and has to re-import nuclear proteins
when matching of tRNA and mRNA codons occur
elongation factor TU is released
what triggers a forward movement of ribosomes
elongation factor G
what may help with ‘walking along the mRNA in order to synthesise a protein ‘molecular ratchet’
a conformational change in the ribosome caused by translation-elongation factor
how many ribosomes will work on a single mRNA molecule and what is this structure called
numerous and known as a Polysome
definition of a protocell
A protocell (or protobiont) is a self-organized, endogenously ordered, spherical collection of lipids proposed as a stepping-stone to the origin of life.
definition of lipid raft
are subdomains of the plasma membrane that contain high concentrations of cholesterol and glycosphingolipids.
