Bio1 Mon 10/19 Lecture: Cell Structure and Membranes + Pre-Class Videos

How do you determine if a molecule can cross the cell membrane through passive/active transport or endo/exocytosis?

Molecules that are small enough can use passive or active transport.

Molecules that are too large (or bulky material) and not dissolved will need endocytosis or exocytosis.

Describe Endocytosis vs Exocytosis.

Endocytosis moves molecules into the cell.

Exocytosis moves molecules out of the cell.

Both use vesicles.

Describe the three types of Endocytosis.

Hint Available

Phagocytosis: part of the cell membrane engulfs the molecule(s), forming a vesicle which then fuses with a lysosome to digest its contents

• Unicellular protists use phagocytosis for feeding. Some white blood cells use it to defend the body by engulfing foreign cells or substances.

Pinocytosis: part of the cell membrane surrounds dissolved substances and fluids to form a vesicle and bring them into the cell

Receptor-mediated endocytosis: used by animals to move specific macromolecules into the cell

• Most mammalian cells use receptor-mediated endocytosis to take up cholesterol packaged in Low-density lipoprotein (LDL) particles.

Explain the process of Receptor-Mediated Endocytosis with one example.

1. Receptors on the cell membrane are clustered together in a coated pit that is reinforced by clathrin. These receptors bind to specific proteins on the LDL particle.

2. More clathrin molecules add to the lattice, eventually pinching off the membrane to form a vesicle containing the target molecule.

3. The vesicle soon becomes uncoated as clathrin dissociate from the vesicle and each other. The clathrin proteins are reused to form other coated vesicles.

4. The vesicle fuses with another vesicle, causing the pH inside the vesicle to drop and causing the receptors to dissociate from the target molecule. The receptors return to the cell membrane to be reused.

5. The vesicle fuses with a lysosome, which breaks down the LDL particle into amino acids and fatty acids, and releases the cholesterol into the cytosol for the cell to use.

Explain the process of exocytosis.

Secretory vesicles fuse with the cell membrane to release their contents outside the cell.

Describe the function of the nucleus. What cells have nuclei?

The nucleus contains the cell’s DNA, the stored genetic instructions of each cell.

Important reactions for interpreting the genetic instructions occurs in the nucleus.

Describe the function of the mitochondria. What cells have mitochondria?

responsible for critical steps in the extraction of energy from food, converting it into a more usable form of energy

It is in almost all eukaryotes, including plants and animals.

Describe the function of the chloroplast. What cells have chloroplasts?

Chloroplasts are where photosynthesis occurs and produces the energy needed for all plants and animals to survive.

They are found in plants and algae, but not in animals.

What is photosynthesis?

the process by which light energy is captured and converted into chemical energy

Describe the structure and function of the endoplasmic reticulum (ER).

a large network of membranes that manufacture proteins and lipids

The rough ER appears rough because it is covered in ribosomes, which make proteins.

The smooth ER does not have ribosomes and instead makes lipids.

Describe the function of the ribosomes. Where are they located?

Ribosomes make proteins and pass newly made proteins into the interior of the ER.

Ribosomes are located on the ER and in the cytoplasm.

Describe the structure and function of the Golgi Apparatus. Include another organelle that aids its function.

a series of flattened membrane compartments that process and package proteins made in the rough ER

Transport vesicles move proteins from the rough ER to the Golgi apparatus.

After the proteins are processed, the vesicles then deliver the proteins to their final destination.

Describe the structure and function of the lysosome.

Click hint after.

It contains digestive enzymes that break down food and various other particles

• These particles can come from outside the cell but also inside the cell (worn out cell organelles and molecules). The subunits from the particles can be used to build new cellular structures.

What are three structures that plant cells have, which animal cells do not?

Chloroplasts

Cell wall

Large central vacuole

Describe the function/structure of the cell wall and the vacuole.

The cell wall is made of cellulose and provides strength and protection.

The vacuole takes up most of the cell in hydrated plant cells.

Together, the cell wall and vacuole keeps the cell rigid, which helps plants stand upright.

Describe the general structure and functions of the cytoskeleton.

In animal cells, the cytoskeleton also…

a network of protein fibers that carry out various functions, including structural support and the movement of structures within cells (internal organization)

In animals, the cytoskeleton also gives the cell the ability to move and maintain its shape.

Describe the structure/function of the two main structures of the cytoskeleton.

Microtubules are stiff, hollow tubes that anchor other organelles and guide the movement of vesicles and other cell components.

Actin are thin, flexible filaments that form cross-linked bundles and branching networks, which power cell movement and muscle contraction

What actually moves molecules along the microtubules?

The motor protein kinesin carries vesicles along microtubules.

Describe how water moves across the cell membrane in two ways.

Water is small enough to cross the membrane by simple diffusion, but does so slowly.

Rapid water transport requires facilitated diffusion through channel proteins called aquaporins.

What is osmosis?

the movement of water across a membrane

Describe active transport.

Hint available

Active transport moves molecules against the concentration gradient.

It requires energy input, either from ATP or a concentration gradient created using energy from ATP.

What is ATP?

2 pts

the energy source for primary active transport

a monomer of RNA (has the nitrogenous base adenosine)

Protein “pumps” are typically associated with…

primary active transport

Compare Primary vs Secondary Active Transport.

Click hint after.

Primary active transport uses energy directly from ATP.

Secondary active transport requires primary active transport and is powered by a concentration gradient instead of directly using energy from ATP.

• Typically, in secondary active transport, one molecule moves against its gradient and one molecule moves with its gradient.

Describe one example of primary active transport and secondary active transport.

Primary active transport: With one molecule of ATP, the sodium–potassium (Na⁺–K⁺) pump moves three Na+ ions out of a cell and two K+ ions into the cell.

Secondary active transport: Energy from the Na⁺ gradient (created through primary active transport) powers secondary active transport that moves Na+ and glucose into the cell. Na+ moves with its gradient and glucose moves against.

Describe/compare the three types of membrane transport.

Hint available.

Uniport: one type of solute molecule is transported. It could be either active or passive transport.

Symport: two or more types of solute molecules are transported in the same direction.

Antiport: two or more types of solute molecules are transported in opposite directions.