lab exam

Question 1

What characteristics make Chlamydomonas reinhardtii a useful model organism for studying cellular processes?

Answer 1

Single-celled and Easy to Grow:
It is a simple, single-celled green algae, easy to grow and maintain in the laboratory.

Two Flagella with “9+2” Structure:
It has two flagella composed of microtubules arranged in a “9+2” pattern, ideal for studying flagella regeneration and cellular movement.

Visible Cellular Components:
Contains distinct structures like an eyespot in its chloroplast, which helps it detect and move toward light, making it useful for studying light response and signal transduction.

Versatile Growth Conditions:
Can grow under different conditions: photoautotrophically (light and CO₂), heterotrophically (organic carbon sources), and mixotrophically (both), making it versatile for various metabolic studies​Lab #1 Slides.

Question 2

How does the 9+2 arrangement of microtubules contribute to flagellar movement?

Answer 2

According to the slides, eukaryotic flagella use a “9+2” arrangement of microtubules, in which nine pairs of microtubules surround two central microtubules. This arrangement provides the structural framework that, when powered by ATP, produces the whip-like motion characteristic of eukaryotic flagella. By sliding against each other (through the action of motor proteins, although not detailed in the slides), the outer microtubule doublets bend the entire flagellum back and forth, enabling the cell to move.

Question 3

Explain the structural and functional differences between eukaryotic and prokaryotic flagella.

Answer 3

Composition

Eukaryotic Flagella: Composed of microtubules made of the protein tubulin, arranged in a characteristic “9+2” structure (nine pairs of microtubules surrounding two central microtubules).
Prokaryotic Flagella: Made of the protein flagellin, with a simpler structure consisting of a basal body, hook, and filament.
Membrane Association

Eukaryotic Flagella: Enclosed by the plasma membrane (i.e., they are an extension of the cell membrane).
Prokaryotic Flagella: Not covered by the cell membrane and protrude directly from the bacterial cell surface.
Movement Mechanism

Eukaryotic Flagella: Bend in a “whip-like” motion powered by ATP-driven interactions between microtubule doublets.
Prokaryotic Flagella: Rotate like a propeller, powered by a proton gradient (H⁺) across the cell membrane.
Location & Complexity

Eukaryotic Flagella: May appear on certain specialized cells (e.g., sperm cells in animals, Chlamydomonas in algae). They often serve functions such as motility or moving fluid over a cell surface (cilia in respiratory tract).
Prokaryotic Flagella: Found on many bacterial species for locomotion, enabling movement toward or away from stimuli. They are structurally less complex than eukaryotic flagella but serve a similar purpose of cellular motility.

Question 4

How does the cytoskeleton contribute to cell movement and stability.

Answer 4

Acts as muscle and skeleton for cell movement and cell stability.

Question 5

What is the role of cycloheximide in protein synthesis and how does it affect translation?

Answer 5

cycloheximide inhibits protein synthesis by blocking translation.

Question 6

Explain how gene expression follows the central dogma of molecular biology.

Answer 6

The flow of genetic information from DNA to RNA to protein.

Question 7

Describe the process of transcription and the role of RNA polymerase.

Answer 7

Transcription is the process where genetic information encoded in DNA is copied into messenger RNA (mRNA). RNA polymerase binds to DNA at the promoter region, unwinds the double helix, and synthesizes a complementary RNA strand by adding RNA nucleotides in a 5’ to 3’ direction.

Question 8

How do second messengers like cyclic AMP (cAMP) and calcium ions amplify signals within a cell?

Answer 8

cAMP:

When a signaling molecule (ligand) binds to a G-protein-coupled receptor (GPCR), it activates an enzyme called adenylyl cyclase.
Adenylyl cyclase converts ATP to cAMP, which then serves as a second messenger.
cAMP activates protein kinase A (PKA), which phosphorylates various target proteins, leading to changes in gene expression, enzyme activity, and other cellular responses.
This amplification occurs because one activated receptor can lead to the production of many cAMP molecules, which in turn activate multiple PKA enzymes, leading to a broad cellular response.
Calcium Ions (Ca²⁺):

A ligand binds to a receptor (e.g., GPCR or receptor tyrosine kinase), triggering the release of inositol triphosphate (IP₃).
IP₃ binds to receptors on the endoplasmic reticulum (ER), causing calcium channels to open and release stored Ca²⁺ into the cytoplasm.
The increase in cytoplasmic Ca²⁺ activates calcium-binding proteins like calmodulin, which then modulate various cellular processes, including enzyme activation, cytoskeletal changes, and gene expression.
Since Ca²⁺ is released from intracellular stores in response to one signal, it rapidly amplifies the effect of the initial ligand binding.