BS1040 Topic 3 Lecture 2 Transmembrane proteins, cellular homeostasis and transport

What structural feature allows proteins to insert into membranes?

A hydrophobic region, often forming α-helices that span the membrane.

How many amino acids are typically needed to span the membrane in an α-helix?

What is the alpha helix structure of a transmembrane?

About 20 amino acids.

They span the membrane. They contain 20 amino acids in length. indicating they have a coarse structure. The amino acid residues are hydrophobic side chains.

What types of amino acid residues are found in transmembrane α-helices?

Mainly hydrophobic residues.

What is the Kyte and Doolittle hydropathy index used for?

Predicting hydrophobic and hydrophilic regions of proteins to identify transmembrane domains. shows whether they have a high affinity of water- higher the score more likely it wants to interact with water

What is a hydropathy plot?

A graph showing the hydrophobicity of amino acid sequences, used to predict transmembrane segments.

What structure forms the transmembrane pore in bacterial porins?

β-strands arranged in a barrel structure (β-barrel).

Why do alternating hydrophobic and hydrophilic amino acids occur in β-barrels?

To allow interaction with both lipid and aqueous environments.

What are integrins?

Glycoproteins that form heterodimers (α and β subunits) linking the extracellular matrix (ECM) to the cytoskeleton.

What are the main functions of integrins?

Cell-ECM adhesion, cell-cell adhesion, and signal transduction.

What extracellular components do integrins interact with?

Fibronectin, laminin, and collagen.

What are other types of cell adhesion molecules?

Cadherins, selectins, and members of the Ig superfamily.

What is the role of transmembrane proteoglycans?

Mediate cell-ECM adhesion and play a role in host-pathogen interactions.

What are the two main classes of transmembrane receptors?

Ligand-gated ion channels and metabotropic receptors (GPCRs, tyrosine kinases).

What are the main types of transmembrane transport proteins?

Channels and carriers.

How do cell membranes differ from pure lipid bilayers in permeability?

Specialized transporters increase permeability for ions and molecules.

Define homeostasis.

The tendency toward a stable equilibrium between interdependent elements, maintained by physiological processes.

maintaining a stable internal environment by physiological environment 

Who developed the concept of homeostasis and when?

Walter Bradford Cannon in the 1920s.

Which earlier physiologist introduced the concept of the 'milieu intérieur'?

Claude Bernard in the 1860s.

What are the three main components of a homeostatic control system?

Variable, sensor, and effector.

What is a 'set-point' in homeostasis?

The target value or range a system tries to maintain.

Why is homeostasis important?

It maintains low entropy and organized conditions necessary for cellular and organismal function.

At what biological levels is homeostasis important?

Cells, organ systems, and the entire organism.

What is the extracellular fluid (ECF) and why is it important?

Fluid surrounding cells that provides a stable environment for cellular function. Control the composition and allow a good volume

What role do epithelial tissues play in homeostasis?

They regulate exchange between the body and the external environment.

What enables regulated exchange between intracellular and extracellular fluids?

The selective permeability of the cell membrane and transmembrane proteins.

Compare calcium ion concentrations across cellular compartments.

Mitochondrial matrix and ER: up to mM; cytosol: 10-100 nM; extracellular fluid: ~2 mM.

How does pH vary between cellular compartments?

Different organelles and compartments maintain distinct pH levels suitable for their functions.

what are types of integral proteins?

Type 1- 6 depend on whether they have a N term outside or a C term outside and whether or not they have polypeptides. Type V & VI form multiple proteins clustered which are covalently bounded.

How is homeostasis achieved?

Via the regulated exchange of molecules/ions between cytosol and extracellular fluid/environment. This can be achieved by the variation in ca+ concentration in different compartments which is lower in the cytosol and the variation of pH( logarthmi scale ) in the compartments of the organelles this makes sure that the organelles are not being denatured etc. So pH in mito is ten fold higher