30 Questions
What is the primary function of membrane receptors?
To allow selective transport of important molecules
What determines the rate of simple diffusion across a bilayer?
The size of the molecule and its association with H2O
How does biology increase the rate of transport of highly polar molecules?
Through facilitated diffusion
What is the purpose of calculating the average hydrophobicity of amino acids in a membrane protein?
To identify hydrophobic regions in the protein
What is the importance of membrane transport in cells?
To acquire raw materials and remove waste products
What type of membrane protein spans the lipid bilayer only once from outside to inside the cell?
Type I
Which amino acid has the highest hydrophobicity score on the scale provided?
Phenylalanine
Which of the following amino acids is classified as hydrophilic according to the hydrophobicity scale?
Serine
How can regions of hydrophobicity in a protein be determined?
Using a scale that converts hydrophobicity to numerical values
Which statement best describes the relevance of the fluid-mosaic model in membrane biology?
The model demonstrates the dynamic movement of lipids and proteins within the membrane.
What is the primary function of membrane proteins that are anchored to the lipid bilayer via a single transmembrane alpha helix?
To facilitate the transport of small molecules across the membrane
Which of the following amino acid sequences is most likely to be embedded in the hydrophobic core of the lipid bilayer?
Nonpolar amino acids with low hydrophobicity scores
What is the significance of calculating the average hydrophobicity of amino acids in a membrane protein?
To predict the protein's localization in the membrane
Which type of membrane protein is most likely to be involved in cell-cell adhesion?
Cell adhesion molecules
What is the primary function of facilitated diffusion in membrane transport?
To increase the selectivity of transport for specific molecules
Which type of membrane protein assembly may form a channel and consists of multiple chains?
Type IV
Which specific amino acid has the highest hydrophobicity score on the provided scale?
Isoleucine
In a Type V membrane protein, how is the polypeptide typically anchored to the membrane?
C-terminal anchoring
What amino acid is classified as hydrophilic according to its hydrophobicity score?
Cysteine
Which type of membrane protein features a single-pass polypeptide with lipid anchoring and is positioned outside-inside the cell?
Type VI
What is the primary function of transporters in membrane proteins?
to transport molecules across the membrane
How do hydrophobic regions of a protein interact with the lipid bilayer?
they associate with the non-polar tails of the phospholipids
What type of membrane protein features a single transmembrane alpha helix?
Type I membrane proteins
Which type of membrane protein is involved in cell-cell adhesion?
Cell adhesion molecules
What is the role of hydrophobicity in determining the structure of a membrane protein?
it determines the regions of the protein that interact with the lipid bilayer
What is the significance of the hydrophobic regions in integral membrane proteins?
Hydrophobic regions in integral membrane proteins reside in the lipid bilayer, allowing the protein to interact with the hydrophobic tails of the phospholipids and stabilizing the protein's position in the membrane.
How do unsaturated fatty acids affect the fluidity of membranes?
Unsaturated fatty acids increase the fluidity of membranes by introducing kinks in the hydrocarbon tails, making it more difficult for the tails to pack tightly together, thus increasing membrane fluidity.
What is the difference between integral and peripheral membrane proteins?
Integral membrane proteins span the lipid bilayer and have regions that are hydrophobic and hydrophilic, whereas peripheral membrane proteins are attached to the membrane but do not span it and are typically hydrophilic.
What is the purpose of calculating the hydrophobicity of amino acids in a protein sequence?
Calculating the hydrophobicity of amino acids in a protein sequence helps identify regions of hydrophobicity, which can determine the protein's ability to interact with the membrane and its function.
What is the characteristic of a Type III membrane protein?
A Type III membrane protein is a multi-pass protein, meaning it spans the lipid bilayer multiple times, forming a single-chain protein.
Study Notes
Membrane Structure and Proteins
- Membrane structure consists of lipids and proteins
- Lipids: phospholipids, sphingolipids, glycolipids, and cholesterol
- Proteins: integral membrane proteins, peripheral proteins, and glycoproteins
- Fluid-Mosaic Model: lipids are the 'fluid' (diffuse laterally), proteins and carbohydrate are the mosaic
Types of Proteins
- Globular proteins
- Fibrous proteins
- Membrane proteins
- Integral membrane proteins: contain hydrophobic and hydrophilic regions, typically α-helical or β-strands/sheets
- Peripheral proteins: attached to the membrane by a lipid anchor
- Enzymatic proteins
- Non-enzymatic proteins
- ECM (Extracellular Matrix) proteins
Integral Membrane Proteins
- Contain regions that are hydrophobic and hydrophilic
- Hydrophobic regions reside in the lipid bilayer
- Hydrophilic regions reside outside the lipid layer
- Loops connecting transmembrane domains (e.g., GPCRs), or large ordered ectodomains/endodomains (e.g., receptor tyrosine kinases)
Types of Integral Membrane Proteins
- Type I: single-pass, N- to C-terminal from outside to inside cell
- Type II: single-pass, N- to C-terminal from inside to outside cell (reverse orientation to Type I)
- Type III: multi-pass (polytopic), single-chain protein
- Type IV: assembly of multiple chains (may form a channel)
- Type V: lipid-anchored protein (typically via palmitoylation or farnesylation of Cys, or N-terminal myristoylation); polypeptide does not pass membrane
- Type VI: single-pass polypeptide with lipid anchoring
- C-terminal anchored: the C-terminal portion of the protein is a transmembrane domain
Amino Acids and Hydrophobicity
- Hydrophobicity has been measured and converted into a scale
- Hydrophilic, neutral, and hydrophobic amino acids
- Water becomes ordered to exclude hydrophobic molecules
- The greater the hydrophobicity, the more water becomes ordered
- Regions of hydrophobicity in a protein can be determined
- Amino acid sequence can be plotted to show average hydrophobicity
Membrane Transport
- Importance of membrane transport:
- Acquire raw materials for biosynthesis and energy production
- Release by-products and waste products of metabolism
- Protect interior from potential external toxic surroundings
- Allow selective transport of important (polar and ionic) molecules through the semipermeable non-polar membrane
- Types of membrane transport:
- Simple diffusion (passive, energy independent)
- Facilitated diffusion
- Active transport (energy dependent)
- Biology has increased the rate of transport of highly polar molecules through specific mechanisms
Learn to calculate the average hydrophobicity of amino acid sequences ranging from 1-6, 2-7, 3-8, and 125-130. Understand the significance of membrane proteins in processes such as transport, cell adhesion, and receptor activity.
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