Lecture 4 Flashcards
(32 cards)
How big are actin filaments?
5-8 nm in diameter
Where are actin filaments usually found?
The periphery of cells (+ the middle of smooth muscle and + throughout the cytosol of the maize epidermis)
How is actin involved in mitosis?
When a cell is about to split, there is a large concentration of actin found where the cell is about to split
What is the function of actin?
It helps define the shape of cells and cellular sub-structures
It also helps in cell movement
What is the lamellipodium?
It is found in the ‘leading edge’ of a cell, it contains a dense meshwork of actin filaments and allows the cell to project forward and move it forward
What are lamins?
They are intermediate filaments found in all animal cells (meshwork of filaments) that are found on the inner leaflet of the nuclear membrane, they help maintain the shape of the nucleus and nuclear envelope
What is the most abundant protein in eukaryotes?
Actin (10% and 15% of proteins bind to actin)
What is actin?
A protein that has 375 amino acids and is around 55kDa, it has 2 similar domains that come together and form an ATP binding region, when ATP is hydrolysed here it become ADP
What is monomeric actin?
Also known as G actin, it has 2 ends: plus end (barbed end) and minus end (pointed end).
It will assemble to form helical fibres (which are microfilaments)
What is actin treadmilling?
Actin molecules migrate from the barbed to pointed end and the plus end seems to grow faster than the minus end, leading to what we see as treadmilling
During this, ATP is hydrolysed to ADP
How are actin-binding proteins regulated?
Certain proteins can bind to monomeric actin and prevent them from binding to other monomeric actin
There can be branching of actin filaments to produce bundles and networks
Severing and annealing of smaller actin filaments
What is myosin?
Bundles of motor proteins that interact with actin during muscle contraction
It is formed by 2 alpha helices that wrap around each other
It has a C and N (N terminus binds to ATP)
What are intermediate filaments?
They provide stability and cohesion against stretch and are found in the cytoplasm and nucleus
What are some cytoplasmic intermediate filaments?
Keratins (epithelia)
Vimentin (connective tissue, muscle cells, glial cells)
Neurofilaments (nerve cells)
What are the nuclear intermediate filaments?
Nuclear lamins
What are keratins?
Fibrous proteins/Intermediate filaments
2 Keratin monomers would come together and form a ‘coiled-coil dimer’ which can bind together and form tetramers and then sheets
What are desmosome?
Connections through cells that allow cells to adhere to each other and allow stability after stretching
What can mutations in keratin do?
This can cause epidermolysis bullosa (splitting of the epidermis layer)
What are microtubules?
Tube-like structure made from alpha and beta tubulin (beta is plus end and alpha is minus end),
What is a protofilament?
A linear chain of microtubule subunits (which one beta and one alpha tubulin is referred to as a heterodimer)
What is one microtubule made of?
13 Protofilaments
What is the function of microtubules?
Allow cargo to be transported from one part of the cell to another
They also used to align the sister chromatids during cell division
What is the centrosome?
The microtubule organising centre
Made of a number of proteins that form a complex to start the polymerisation of tubulin monomers into microtubules
What are MAPs?
Microtubule associated proteins (eg: MAP2 and tau) and they are involved in microtubule stability
