Seminar 3 Flashcards
Can you identify the three different ways that a molecule can cross a cell membrane and explain why it is called like that?
- Three Ways Molecules Cross the Cell Membrane
a. Passive Diffusion
• What it is: Molecules move from high to low concentration directly through the lipid bilayer.
• Why it’s called that: It’s “passive” because it doesn’t require energy (ATP).
• Example: Oxygen, CO₂, and small lipophilic molecules.
b. Facilitated Diffusion
• What it is: Molecules move down their concentration gradient but need help from a membrane protein (channel or carrier).
• Why it’s called that: It’s “facilitated” because a transporter assists the movement.
• Example: Glucose via GLUT transporters.
c. Active Transport
• What it is: Molecules move against their concentration gradient, using energy (usually ATP).
• Why it’s called that: It’s “active” because it requires energy input.
• Example: Sodium-potassium pump (Na⁺/K⁺-ATPase).
Can you describe per macronutrient (more specifically: glucose, fatty acid and amino acid) how it is transported into a cell?
Glucose
• Enters cells via GLUT transporters (facilitated diffusion).
• GLUT4 is insulin- and exercise-responsive (especially in muscle and fat cells).
• GLUT2 is found in the liver (hepatocytes) for bidirectional glucose flow.
Fatty Acids
• Transported by fatty acid transport proteins (FATPs), CD36, and also by passive diffusion to some extent.
• Once inside, fatty acids are bound to FABPs (fatty acid-binding proteins).
Amino Acids
• Transported via specific amino acid transporters (e.g., LAT1, SNATs).
• Transport mechanisms vary (facilitated diffusion or active transport depending on the gradient and amino acid type).
Can you list the names of transporters needed for crossing the cell membrane. Specifically focus on the differences of transporters among the different organ cells (myocyte, hepatocyte, adipocyte).
Transporters by Organ Cell Type
Myocytes (Muscle Cells)
• GLUT4: Glucose uptake (insulin and exercise-sensitive).
• CD36: Fatty acid uptake.
• Amino Acid Transporters: For branched-chain amino acids, e.g., LAT1.
Hepatocytes (Liver Cells)
• GLUT2: Glucose uptake and release (bidirectional, high-capacity).
• FATP2, FATP5: Fatty acid transport.
• Amino Acid Transporters: e.g., SNAT2, ASCT2 for neutral amino acids.
Adipocytes (Fat Cells)
• GLUT4: Glucose uptake (insulin-responsive).
• CD36: Fatty acid uptake.
• Amino Acid Transporters: e.g., PATs and LAT1 for certain amino acids.
Can you introduce the concept and importance of a signalling transduction pathway/signalling cascade?
- Signal Transduction Pathway / Signaling Cascade
Definition:
A signaling cascade is a chain reaction triggered by a signal (like a hormone or growth factor) binding to a receptor on the cell membrane. This activates a series of proteins inside the cell, often involving phosphorylation, ultimately leading to a specific cellular response (e.g., gene expression, metabolism changes).
Importance:
• Allows amplification of signals (one signal → many responses).
• Enables tight regulation and integration of multiple signals.
• Critical in processes like growth, immune responses, metabolism, and cell survival.
Can you explain the role that GLUT4 has in skeletal muscle glucose uptake and how it’s translocation to the membrane is linked with exercise and high blood glucose?
Role of GLUT4 in Skeletal Muscle Glucose Uptake
• GLUT4 is a glucose transporter stored inside muscle (and fat) cells.
• When insulin levels rise (e.g., after eating) or during exercise, signaling pathways (like PI3K-Akt for insulin and AMPK for exercise) trigger GLUT4 translocation to the cell membrane.
• Once at the membrane, GLUT4 facilitates glucose entry into the muscle cell, where it is used for energy or stored as glycogen.
Can you link the role that GLUT4 has in type 2 diabetes?
GLUT4 and Type 2 Diabetes
• In type 2 diabetes, cells become insulin-resistant, meaning insulin signaling is impaired.
• As a result, GLUT4 translocation is reduced, leading to decreased glucose uptake in muscle and fat cells.
• This contributes to elevated blood glucose levels (hyperglycemia).
• Regular exercise can help because it stimulates GLUT4 movement to the membrane independently of insulin via AMPK activation.
