VESICULAR TRANSPORT & AMOEBOID MOVEMENT2

8/7/2019 VESICULAR TRANSPORT & AMOEBOID MOVEMENT2

http://slidepdf.com/reader/full/vesicular-transport-amoeboid-movement2 1/48

MEMBERS:

Maryann Andrew

Joanne Beejaimal

Jessica Bruzon-SurreyAllincia Michaud

Stephan Muridall

Herawattie Persaud

Swarastie PersaudJoshua Ramah

Drohinath Singh

Aartie Somwaru

Jomane Thompson



� Cytosis is a special kind of transport mechanism which involves themovement of water and other molecules into (endocytosis) and out of

(exocytosis) a cell.

� During this movement all molecules must pass through the cell·s plasma

membrane.

�� By far the most important type of movement that occurs in the body is

that of the muscle cells, however there are other types of movements

that play important roles in the human organism e.g amoeboid

movement, which is the movement of an entire cell in

� relation to its surroundings. It receives its name from amebae and thefact that they move in this manner.

� This presentation seeks to study the characteristics of these processes in

recognition of their importance in the body.



� Cell membrane described as a lipid bilayer.

� Double layer of lipid one molecule thick.

� Basic bilayer composed of phospholipids molecules.

� Phosphate end hydrophilic and fatty acid end hydrophobic.

� The hydrophobic portion of the phospholipids has a tendency to

attach to one another in the middle of the membrane, since

these molecules repel water, while the hydrophilic portion

constitutes the inner and outer surfaces of the cell membrane.



� The layer in the middle of the membrane is impermeable to

water soluble substance such as glucose and urea. This portion

can however be penetrated by oxygen, carbon dioxide and

alcohol (fat soluble substances).



1. Integral Proteins

Penetrates throughout the entire membrane. Provides channel

for water soluble substances. Take part in active transport

(carry molecule in opposite direction to natural transport). Acts

as receptors, enzymes.

2. Peripheral Proteins

Attaches to surface of plasma membrane. Functions entirely as

enzymes/controller of transport through cells in membrane

pores.



Glycocalyx-loose carbohydrate coat outside cell membrane.

Function

1. Has negative electrical charge, giving cell an overall

negative charge.2. Cell adhesion.

3. Receptor for binding hormone such as insulin



� Cholesterol, a form of lipids that are dissolved in the bilayer of

the membrane and determines the permeability and fluidity of

the membrane as well.



� Endocytosis is the process by which extracellular substances are

imported into the cell via transport vesicles because it cannot

cross the hydrophobic plasma membrane. This process requires

a lot of energy in the form of adenosine triphosphate (ATP), the

chemical compound used as energy in the majority of cells.

� There are two main forms of endocytosis, namely

phagocytosis and pinocytosis.



� The basic difference between these two processes can be easily

distinguished from their names.

� Pinocytosis (cell drinking) involves movement of small particles

into the cell from the extracellular fluid (ECF) whereas� Phagocytosis (cell eating) involves the movement of large

particles into the cell from the ECF.



� Both phagocytosis and pinocytosis take place by the same basic

mechanism which occurs as follows:

1. On the cell membrane there are receptors found in coated pits

for the substance which is to be imported into the cell.2. Beneath the pits, on the inside of the membrane are fibrillar

proteins called clathrin.When the receptors bind to the

particle, a series of other processes are activated.

3. First there is an invagination of the pit, with the fibrillar

proteins working to wrap the edges of the pit around the

product, enclosing it along with some ECF.



4. Once completely invaginated, contractile proteins, actin

and myosin, cause the vesicle to be ´pinchedµ off the cell

membrane, forming either a pinocytic or phagocytic

vesicle. Energy in the form of ATP is required.

5. The receptors are now removed from the vesicle to be

sent back to the surface to be recycled. The new vesicle

now contains no receptors.6. The new vesicle then fuses with a lysosome and forms a

secondary lysosome. The enzymes of the lysosome then

hydrolyse the particles which are subsequently released

into the cytoplasm of the cell.



� Phagocytosis is the process by which certain living cellstermed ´phagocytesµ ingest or engulf other cells or

particles.

� The phagocyte may be a free-living one-celled organism,

such as an amoeba, or one of the body cells, such as a

leukocyte (white blood cell).

� In some organisms, such as amoebas and sponges,

phagocytosis is a means of feeding; in higher organisms

phagocytosis is chiefly a defensive reaction against

infection and invasion of the body by foreign substances.



� Phagocytes include neutrophils, monocytes, macrophages,

dendritic cells, mast cells, fibroblasts, and erythrocytes.� Phagocytosis mainly occurs in tissue macrophages and

neutrophils.

� The particles commonly phagocytosed by leukocytes

include bacteria, dead tissue cells, protozoa, various dustparticles, pigments, and other minute foreign bodies.

� It is initiated when these foreign bodies bind with the

surface receptors in the coated pits.



� The process of phagocytosis is an immune response.

� Macrophages are termed antigen presenting cells, as they take

antigen to T cells to be killed.

� Lymphokines are involved in the immune response, which areproduced by lymphocytes and play a role in attracting other

immune cells to an affected area.



� Macrophages found in the lungs can phagocytose particles

trapped in the alveoli.

� If the particle is digestible, the digestive products are released

into the lymph.� Otherwise, the macrophage will form a capsule around the

particle resulting in its degradation.



� In the proximal tubule, the reabsorption of large molecules

such as proteins occurs.

In this process:

� The protein attaches to the brush border of the luminalmembrane.

� This portion of the membrane then invaginates until it iscompletely pinched off and a vesicle is formed containing theprotein.

� Once inside the cell, the protein is digested into its constituentamino acids, which are reabsorbed through the basolateral

membrane into the interstitial fluid.

NOTE: This requires energy, it is considered a form of activetransport.



� This is a process through which a cell expels molecules and other

objects that are too large to pass through the cell membrane

structure. It describes the process of vesicles fusing with the

plasma membrane and releasing their contents to the outside of

the cell.

� Simply put it is all the mechanisms involved that facilitate

movement from the cytoplasm to the interstitial fluid. Contents of

these vesicles may be excretory products, hormones,

neurotransmitters etc



Constitutive Secretion

In constitutive secretion the protein is sorted into vesicles in the Golgi apparatus

and moves directly to the cell surface membrane. This results in the release of

soluble proteins to the exterior.

Regulated Secretion

Regulated secretion requires an external signal,

a specific sorting signal coat as well as

intracellular calcium.



Exocytosis occurs in five stages:

1. Vesicle trafficking ² vesicle containing excretory products istransported through the cytoplasm towards the cellmembrane i.e. towards point of deposition

2.Vesicle tethering ² vesicle is suspended and pulled towardpoint of expulsion

3. Vesicle docking ² vesicle comes into contact with the cellmembrane, where it begins to chemically and physicallymerge with the cell membrane proteins.

4. Vesicle priming ² In those cells where chemical transmitters arebeing released, this step involves the chemicalpreparations for the last step of exocytosis.



� 5. Vesicle fusion - Proteins from the walls of the vesicle

merge with the cell membrane and breach, pushing the

vesicle contents out of the cell and into the interstitialfluid.



Diagram showing process of exocytosis



Many cellular processes involve exocytosis. Examples ofthese processes within the human body are:

� Hypothalamic hormone release

� Secretion of proteins like enzymes, peptide hormonesand antibodies from cells.

� Release of neurotransmitters from presynaptic neuronse.g. acetylcholine release

� Acrosome reaction during fertilization� Recycling of plasma membrane bound receptors

� Insulin release from pancreatic cells



� Acetylcholine is a neurotransmitter necessary for muscular

functions.

� It is secreted in cytoplasm of terminal boutons then absorbed

into synaptic vesicles.� Dense bars present on neural membrane have protein particles

which act as voltage-gated calcium channels.

� These channels open when there is an action potential and allow

Ca2+ to diffuse from synaptic space into the bouton

� Ca2+ attracts the vesicles drawing them to the membrane with

which they fuse and are then exocytosed.



Diagram showing release of acetylcholine at a neuromuscular

junction.



Factors that play a regulatory role in exocytosis include:

� Nitric oxide

� Calcium concentration

� Glucose concentration [in the case of insulin secretion]



� Cellular movement is a cyclical process which is driven primarily

by actin polymerization and acto-myosin contractility.

� Cells in the body exhibit three main types of movements: amoeboid

ciliary

muscular.



� Ciliary Movement: occurs in most of our internal tubular organs

which are lined by ciliated epithelium.

For example:� The coordinated movements of cilia in the trachea help us in

removing dust particles and some of the foreign substances

inhaled along with the atmospheric air.

� Passage of ova through the female reproductive tract is alsofacilitated by the ciliary movement.



� Muscular Movement:Movement of our limbs, jaws,tongue, etc, require muscularmovement. The contractileproperty of muscles are effectively

used for locomotion and othermovements by human beings andmajority of multicellular organisms



� A moeboid movement is brought about by

reversible changes in the actin filaments of the cell'scytoskeleton.

� Cross-linking of these filaments by other proteinscreates a three-dimensional network with gel-likeproperties of the cell.

Key steps in amoeboid locomotion are:� protrusion of the leading edge of the cell,

� adhesion of the leading edge and release at the cellbody and rear

� cytoskeletal contraction to pull the cell forward.



� A s a cell moves towards a substrate, it experiencesexternal forces, which include the viscous force or

resistance from the surrounding medium andcell-substrate interaction forces, and internal forcesthat are generated by the cytoskeleton.

� The cytoskeleton is the essential component increating these motility-driving forces, and incoordinating the entire process of movement.

� The cell propels the membrane forward by orienting and reorganizing (growing) the actinnetwork at its leading edge.

� A s the leading edge begins to protrude, adhesionmolecules gathered in the extending region helpattach the leading edge to the substrate.



� Cell-substrate attachments are created at theleading edge when actin bundles link thecytoskeleton to the substrate at certain sites via

adhesion molecules

� A s the cell continues to adhere at the leading edge,it releases from the cell body and rear of the cell,possibly by the disassembly or contraction of its

attachments (actin bundles).

� At the rear the receptors are pulled away from theirligands. This leads to the formation of new endocytoticvesicles.

� Within the cell, these vesicles stream toward thepseudopodial end of the cell, where they are used toform still new membrane for the pseudopodium.



� The rest of the cell is pulled forward, mainly by contractile forces that are produced by myosinmotors sliding on actin filaments, which are in the

cell body and at the rear.



� White Blood Cells exhibit ameboid movement when they

move out of blood into tissues as tissue macrophages.

� Fibroblasts utilize ameboid movement to repair damaged

tissues.

� Embryonic cells also use ameboid locomotion to migrate from

their sites of origin to other areas.

� Germinal cells of the skin move towards a cut area by this

type of locomotion.



� Chemotaxis is the most essential initiator of Ameboid movement.

� Most of the cells that exhibit ameboid locomotion move toward

the source of a chemotactic substance; that is, from an area

of lower concentration toward an area of higher concentration;

which is called positive chemotaxis. On the other hand, some

cells move away from the source, which is called negative

chemotaxis.

� The side of the cell most exposed to the chemotactic substance

develops changes in the membrane that causes protrusion of the

pseudopodium.



� Ananthakrishnan R, Ehrlicher A. The Forces Behind Cell Movement. Int J Biol

Sci 2007; 3:303-317. Available from http://www.biolsci.org/v03p0303.htm

� Guyton Textbook of Medical Physiology; 11th Edition

� www.britannica.com/EBchecked/topic/454919/phagocytosis

� http://www.bookrags.com/research/nutrition-and-nutrient-transport-to-wap/

� http://www.answers.com/topic/pinocytosis

� www.newworldencyclopedia.org/entry/Phagocytosis

� http://www.biology-online.org/dictionary/Pinocytosis

� http://www.medterms.com/script/main/art.asp?articlekey=14505

VESICULAR TRANSPORT & AMOEBOID MOVEMENT2

Documents

Transcript of VESICULAR TRANSPORT & AMOEBOID MOVEMENT2