study questions topics 11 and 12

Question 1

Explain reasons why cells need to communicate. Think of reasons for both
multicellular and unicellular organisms.

Answer 1

Cells need to communicate to coordinate activities and respond to their environment, which is essential for survival. In multicellular organisms, communication regulates growth, development, immune responses, and homeostasis, ensuring that different cells work together effectively (e.g., neurons transmitting signals or hormones regulating metabolism). In unicellular organisms, signaling helps in detecting nutrients, avoiding threats, and coordinating group behaviors like quorum sensing in bacteria, which enables collective actions such as biofilm formation. Overall, cellular communication is crucial for adapting to environmental changes, maintaining function, and coordinating biological processes.

Question 2

Describe how plant cells vs. animal cells handle direct signal transfer

Answer 2

Plant cells use plasmodesmata, channels that connect adjacent cells through their cell walls, enabling direct signaling through the cytoplasm. In contrast, animal cells utilize gap junctions, protein channels that link the cytoplasm of neighboring cells for direct communication, as well as synapses for neurotransmitter signaling between nerve cells. While both mechanisms allow for rapid communication, plant signaling is more focused on coordinating growth and development, while animal signaling often regulates more complex processes like muscle contraction and neural activity.

Question 3

How might intracellular receptors differ from receptors anchored in the membrane?
Think about the properties of their signaling molecules as well as their mechanisms
of action

Answer 3

Intracellular receptors bind to signaling molecules that are small and nonpolar, such as steroid hormones, which can diffuse through the cell membrane. In contrast, membrane-bound receptors interact with larger or polar signaling molecules like peptides and neurotransmitters, which cannot cross the lipid bilayer. Intracellular receptors typically act as transcription factors to regulate gene expression, while membrane-bound receptors activate intracellular signaling cascades, often through second messengers, to initiate cellular responses.

Question 4

Describe the process of a phosphorylation cascade AND how it can lead to signal
amplification

Answer 4

A phosphorylation cascade is a series of sequential protein phosphorylations, where one kinase enzyme activates another by transferring a phosphate group from ATP. This cascade leads to signal amplification because each activated kinase can phosphorylate multiple target proteins, exponentially increasing the response. As the cascade progresses, a small initial signal can result in a large cellular response, ensuring an efficient and amplified reaction to stimuli.

Question 5

Intracellular receptors change the generic signaling pathway due to some of their
unique properties. First explain what has to be true of the signaling molecule for an
intracellular receptor to work, then explain why this mechanism compresses the
generic signaling pathway

Answer 5

For an intracellular receptor to work, the signaling molecule must be small and nonpolar (lipophilic) so that it can easily diffuse across the plasma membrane (e.g., steroid hormones like estrogen or testosterone). Unlike membrane-bound receptors, intracellular receptors are located in the cytoplasm or nucleus, meaning the signaling molecule directly binds to them inside the cell. This compresses the generic signaling pathway because it bypasses the need for extracellular receptors and complex transduction cascades like phosphorylation cascades. Instead, once activated, the intracellular receptor often functions as a transcription factor, directly regulating gene expression and producing a faster, more targeted response.

Question 6

Name the enzymes involved in DNA replication and explain their roles.

Answer 6

Enzymes Involved in DNA Replication & Their Roles
Helicase – Unwinds and separates the DNA double helix at the replication fork.
Single-Strand Binding Proteins (SSBs) – Stabilize the separated DNA strands to prevent them from reannealing.
Topoisomerase – Relieves the twisting tension ahead of the replication fork by cutting, swiveling, and rejoining DNA strands.
Primase – Synthesizes a short RNA primer to provide a starting point for DNA polymerase.
DNA Polymerase III – Extends the new DNA strand by adding nucleotides in the 5’ to 3’ direction.
DNA Polymerase I – Replaces RNA primers with DNA nucleotides.
Ligase – Seals the gaps between Okazaki fragments on the lagging strand by forming phosphodiester bonds.