8,11 Flashcards
Why can two different cell types with the same DNA be so different?
Different cell types express different genes, leading to the production of different proteins, which define the cells’ structure and function.
How is gene expression regulated in cells?
Gene expression can be controlled at multiple levels, including transcription initiation, RNA processing, mRNA export from the nucleus, mRNA stability, translation, and protein activity.
What is the function of the promoter region in gene expression?
The promoter contains sequences where RNA polymerase binds to initiate transcription.
How do regulatory proteins control transcription?
Regulatory proteins bind to specific DNA sequences (regulatory sequences) to switch genes on or off by interacting with RNA polymerase.
What is an operon in bacteria?
An operon is a set of genes transcribed into a single mRNA molecule and controlled by a single promoter.
How does the lac operon function?
The lac operon is controlled by an activator (CAP) and a repressor. When glucose levels are low, CAP binds and helps RNA polymerase initiate transcription if lactose is present to remove the repressor.
What are transcription factors in eukaryotes?
Transcription factors are proteins that assemble on promoters to help RNA polymerase initiate transcription.
What is the role of the TATA box in eukaryotic transcription?
The TATA box is a DNA sequence that helps position RNA polymerase and transcription factors at the correct site to start transcription.
How do glucocorticoid hormones influence gene expression?
Glucocorticoid hormones bind to receptors, which then bind to DNA and activate genes involved in glucose production, particularly during starvation or stress.
What is a key difference between transcription in bacteria and eukaryotes?
In eukaryotes, transcription requires multiple transcription factors, whereas bacterial RNA polymerase can initiate transcription on its own.
What is the main function of the plasma membrane?
The plasma membrane acts as a selective barrier, allowing the passage of nutrients and waste and containing proteins that sense environmental signals.
What are endocytosis and exocytosis?
Endocytosis is the process of importing materials into the cell, while exocytosis is the export of materials out of the cell.
What is the basic structure of the plasma membrane?
The plasma membrane consists of a lipid bilayer, composed mainly of phospholipids with hydrophilic heads and hydrophobic tails.
What is the role of cholesterol in the plasma membrane?
Cholesterol helps modulate membrane fluidity and stability by filling gaps between phospholipids.
What factors affect membrane fluidity?
Membrane fluidity is affected by the length of the hydrocarbon tails, the degree of unsaturation (double bonds), and the presence of cholesterol.
How does cholesterol affect membrane fluidity?
Cholesterol reduces fluidity by filling spaces between phospholipids and making the membrane more stable.
What are the main functions of membrane proteins?
Membrane proteins function as transporters, anchors, receptors, and enzymes.
How do transmembrane proteins interact with the lipid bilayer?
Transmembrane proteins span the lipid bilayer, with hydrophobic regions interacting with the tails of phospholipids and hydrophilic regions interacting with the cytosol and extracellular space.
What is the cell cortex?
The cell cortex is a protein framework that reinforces the plasma membrane. In red blood cells, the protein spectrin forms a meshwork that provides structural support.
What is the function of glycoproteins and glycolipids on the cell surface?
Glycoproteins and glycolipids are involved in cell recognition, protection, and providing a slimy surface to help cells move and prevent them from sticking together.
How do carbohydrates help immune cells like neutrophils recognize infection sites?
Carbohydrates on neutrophils bind to lectin proteins on endothelial cells at infection sites, guiding the neutrophils to the site of infection.
