Cell Biology and Neuroscience - KCL CYO

Peroxisomes

Degrade fatty acids and toxic compounds
Oxidation produces hydrogen peroxide
Produces heat and precursors biosynthetic pathways

Lysosomes

Degrade unwanted proteins and particles with digestive enzymes

Smooth endoplasmic reticulum

Steroid hormone synthesis
Detoxification of organic compounds
Glycogen release in liver

Cytosol

Cytoskeleton
Protein fibre network
Maintain shape
Help with movement
Inclusion bodies and metabolic enzymes

sub cellular fractionation

1. Differential velocity centrifugation
2. Equilibrium density centrifugation

Separate large numbers of organelles for biochemical studies of organelle function

Cytoskeleton

Network of interconnecting protein filaments from nucleus to cell membrane
Movement, shape and cell division

3 types of fillament in cytoskeleton

Microfilaments (actin)
Microtubules
Intermediate filaments

Actin

Strong thin and flexible
Chain of twisted globular actin proteins
Barbed - positive
Pointed - negative
Myosin binds to it

Polarity of actin

All filaments point in same direction
+ve all at one end
Faster growth at +ve end
More loss at -ve
Thus. Treadmilling

ATP and actin

ATP on at barbed
ADP off at pointed

Nucleation of actin

ATP-G-actin forms a trimer
(Rate limiting as unfavourable)
More ATP-G-actins bind
Filament polymerises

Disassembly of actin

After time the ATP is hydrolysed to ADP
ADP-F-actin formed
Destabilises the filament
Unbinds
(Treadmilling)

3 examples of things that regulate Actin polymerisation

- actin monomer Binding proteins
- actin nucleators
- actin filament capping proteins

Actin and myosin?

Muscle contraction
Myosin head binds to actin
Tail forms myosin filaments - grow along actin when contracting (towards Z discs)
Myosin II forms thick filament in muscle

Actin and protrusion

Barbed end faces membrane
Fillament attaches to surface of cell
Polymerises at barbed end
Pushing membrane out
Retraction at rear is mediated by myosin motors pulling on bundles of actin filament

Shapes caused by actin

Lamellipodia
Filopodia

Microtubules

Alpha and beta tubulin bound to GTP or GDP
all arranged in same direction- polar
Beta-tubulin = +ve end. Polymerise faster

Where are microtubules from?

Centrosome
MTOC
Nucleation from Y-tubulin Rings in MTOC (centrosomes or basal bodies in cilia and flagella)
MTs nucleation from centrosome to cell periphery

Microtubules instability

Grow and rapidly shorten
Hydrolysis of GTP bound to beta-tubulin forms GDP-tubulin. Unstable

Role of GTP-cap

Keeps microtubules stable

Example targets for microtubules

Centrosome - mitosis
Deliver vesicles to plasma membrane

What are Dyneins and Kinesins

Dyneins - move cargo towards minus end
Kinesins - move cargo to plus end

Regulation of MT

Stabilising microtubules associated proteins
Destabilising microtubule associated proteins

Intermediate filament role

Prevent excessive cell stretching
Good tensile strength
NOT involved in intracellular movement of vesicles
Reinforce axons of nerve cells
Form 2D mesh in nuclear lamina of nucleus

desmosomes and hemidesmosomes

Des - anchor intermediate filament to adjacent cells
Hemides - connect intermediate to ExtraCellular Matrix (ECM)

Are intermediate filaments polar?

No

two kinds of extracellular matrix and their differences

Epithelium - cells tightly packed on basal lamina
Mesenchyme - cells spread sparsely in 3D fibrillar matrix

basal lamina info

underlies all epithelia and surrounds cells
made of - collagen IV, laminin, nidogen, perlecan

what is fibrillar matrix made of

colagen I, Firbronectin, Elastin, Proteoglycans

what are junctional complexes?

structures of the cell that enable adhesion

name the 6 cell junctions

Gap junction, Focal Adhesion, Hemidesmosome, Desmosome, Adherens junction, tight junction

tight junction

belt shape
hold cells so close it isolates two domains (makes two air gaps)
separates apical and basal domains
e.g. lumen of the gut

Adherens Junction

bind actin filaments from inside the cell
belt shape
hold cells close
strength and flexibility

Desmosome

bind intermediate filaments
spot shaped

Hemidesmosome

spot shape
anchor cell to surface of basal lamina
bind intermediate filaments
defects can cause skin blisters

Gap Junction

spot shape
communicate cells to one another
made of protein channels

Focal Adhesion

spot shape
anchor cell to surface or basal lamina
bind actin filaments

Fluid mosaic model

selectively permeable membrane
block passage of almost all water soluble molecules
ALLOWS small uncharged/hydrophobic molecules through
charged polar require specialist proteins

partition coefficient

equilibrium constant for partitioning of a molecule between oil and water
Kow
higher value = more lipid soluble

how to get Kow

1. fill beaker with ½ water and ½ oil (octanol)
2. add desired molecule, mix and shake
3. wait until separation of both liquids and measure the conc. of the molecule in each one
4. divide conc. in oil/ conc. in water

facilitated diffusion

Movement of specific molecules across cell membranes through protein channels
often gated channels i.e. by voltage, ligand or mechanically
OR carrier protein - conformational change

types of facilitated diffusion

uniport >
antiport --> <--
symport --> --->

compare graph for simple and carrier mediated diffusion
(rate = y) (external conc = x)

simple - straight line, conc increase as constant rate
carrier-mediated = rate faster at the start then levels off as reaches a limit because carriers become staurated

Km and affinity

lower the Km, the less conc. needed to reach half the max speed
lower Km = higher affinity

Why do we have different glucose transporters

They have different affinity. So can use Lower affinity when you don't want to loose much of a substance e.g. glucose in the liver

active transport

Primary - ATP
Secondary - electrochemical gradient

primary active transport

Energy from hydrolysis of ATP
Drives energetically unfavourable biochemical process

Bacteria

Never undergo apoptosis

What is apoptosis?

programmed cell death that occurs in multicellular organisms, helping to eliminate unnecessary or damaged cells.
binding labelled annexin V helps detection
helps in cases like cancer

Prophase I

the first stage of meiosis, where homologous chromosomes pair and exchange genetic material through synapsis and crossing over. primary oocytes are found in this stage

Down’s Syndrome is caused by what?

a failure at the mitotic spindle checkpoint

How do macrophages recognise bacteria?

They have receptors which bind antibodies to the bacterial surface.

How does cholera toxin cause diarrhoea?

disrupts the intestinal cell's ability to absorb water by increasing cyclic AMP levels, causing a large efflux of Cl- ions = excessive secretion of electrolytes and water into the intestinal lumen.

How does Hydra vulgaris reproduce?

primarily reproduces asexually via budding, where an outgrowth forms on the body and eventually detaches to become a new individual. They can also reproduce sexually under certain environmental conditions.

In embryonic development, which germ layer are skeletal muscles derived from?

The mesoderm

What can cause the inhibition of a neuron?

The opening of CL- channels which increases the negative charge inside the neuron, making it less likely to fire an action potential.

What does a lack of oxygen cause on a cellular level?

Necrosis

What does the signal recognition particle bind to?

The ER signal sequence

What is the cell cycle restriction point?

A checkpoint in the G1 phase, where cells are kept from dividing unless they receive a positive signal

What is the effect of increased levels of insulin on the glucose transporter protein GLUT4?

Promote translocation of GLUT4 to the plasma membrane, facilitating glucose uptake into cells.

What is the name of a cell-to-cell signalling mechanism that relies on the transport of signalling molecules via the bloodstream?

Endocrine signaling

What is the resting potential of a typical mammalian neuron?

-70 mV

What is the role of lymph nodes?

The site of interaction between lymphocytes and antigens

Which gene segments first undergo recombination to assemble a functional immunoglobulin?

Heavy chain D to J recombination

What provides the energy for the fusion of a vesicle with its target membrane during membrane trafficking?

conversion of trans-SNARE to cis-SNARE

What tags a protein for import into mitochondria?

A stretch of alternating hydrophobic and positively charged amino acids

What triggers an action potential?

The rapid depolarization of a neuron's membrane due to the influx of sodium ions.

When are the levels of cyclin B the highest during the cell cycle?

Mitosis

Where are embryonic stem cells obtained from?

Inner cell mass of the blastocyst

What is a blastocyst?

early embryonic stage of development
Consists of an inner cell mass containing embryonic stem cells, trophoblast layer forming outer sphere of cells.

Where are T cells initially generated?

T cells are initially generated in the bone marrow.
Migrate to the thymus for maturation.

Where do you find CNS neurons?

brain and spinal cord

Which cell organelle is Nissl substance associated with?

Rough endoplasmic reticulum

What is Nissl substance?

Granules in the cytoplasm of nerve cell bodies.
Consist of aggregates of free polyribosomoes and rER

Which cellular process is defective in L-cell disease?

Targeting of proteins to lysosomes

Which cellular process is ‘hijacked’ by Salmonella?

Macropinocytosis

What is macropinocytosis?

Process where cells take up large volumes of fluid through extensions of their cell surface = membrane sheets protrude outwards
Involves the formation of vacuoles, rearrangement of actin filaments = essential for engulfing the fluid.

Which factor directs the shuttling of proteins from the nucleus into the cytoplasm?

Exportin

What is exportin?

Protein involved in signalling-dependant transport from the nucleus to the cytoplasm.
Opposite transport uses importin

Which homophilic, calcium-dependent transmembrane protein enables cell-cell adhesion at adherens junctions?

Cadherin

Which cells produce cerebrospinal fluid?

Choroid plexus epithelium cells

Adaptive immunity

It’s acquired immunity. always has memory

Which organelle is particularly abundant in secretory cells?

rER

Which part of the cytoskeleton interacts with myosin filaments during muscle contraction?

Actin filaments

Which second messenger mediates the increase of glucose in muscle cells in response to adrenaline?

cAMP

Which structure connects the third and fourth ventricles of the brain?

Cerebral aqueduct

Why can drugs that interfere with microtubule dynamics be used to treat cancer?

they prevent the proliferation of cancer cells by disrupting the mitotic spindle

How do bacteria reproduce?

Binary fission
1. Circular DNA replicates. Both copies attach to cell membrane
2.Plasmids replicate
3.Cell membrane grows between 2 DNA molecules
4.Pinches them inwards, divides cell into 2
5. Cell wall forms, dividing the 2 genetically identical daughter cells

Bacterial reproduction

Uses multifork replication
Multiple rounds of DNA replication to upkeep with cytokinesis
Rapid because new round of DNA replication can start before previous one finishes

PAX6 gene

Codes for protein PAX6
Regulates gene transcription
Involved in eye, nose, CNS and pancreas development

Where is mitochondria thought to originate from?

From bacteria that invaded the ancestral eukaryotic cell

Rab GTPases

Regulates compartmental specificity along endocytic pathway

Intrinsic apoptosis pathway

Involves the release of cytochrome c into the cytoplasm

Neuron

nerve cell that processes and transmits info via electrochemical signalling

Different types of neurons

unipolar neuron has only one process - dorsal root spinal ganglia
bipolar neuron has one dendrite and one axon - vestibular ganglion
multipolar neuron has multiple processes - motor neurons

Astrocytes

Found in CNS
Maintain blood brain barrier by controlling levels of neurotransmitter around synapses
by regulating ions and providing metabolic support

Ependymal cells

Found in CNS
Line the central canal of spinal cord and ventricles of brain
Involved in cerebrospinal fluid production

Ogliodendrocytes

Found in CNS
Myelinate CNS axons
Provide structural framework

Microglia

Found in CNS
Brain’s immune cells
Remove dead cells and pathogens by phagocytosis

Satellite cells

Found in PNS
Surround neuron cell bodies in ganglia
Regulate neurotransmitter levels