biology chapter 5

How are mitochondria and chloroplasts different from other cellular organelles? How does the endosymbiotic theory explain the origins of these organelles?

"Endosymbiosis"-theory of the mitochondria and chloroplast living inside the cell -used to be bacteria and were swallowed by primitive eukaryotic cells Mitochondria - Aerobic respiration occurs in the mitochondrial matrix (krebs cycle) Chloroplast -structure is similar to cyanobacteria

What kinds of molecules are prevented from diffusing directly across a cell membrane?

-ions -large polar molecules (such as glucose)

How is the direction of diffusion of glucose controlled? In other words, if glucose can enter the cell, what keeps it from leaving?

A glucose molecule is too large to pass through a cell membrane via simple diffusion. Instead, cells assist glucose diffusion through facilitated diffusion and two types of active transport

How would you tell the difference between a fat (triglyceride) and a phospholipid? Why are phospholipids much better than fats and oils at forming cell membranes?

A phospholipid contains a phosphate group in the head, where triglyceride does not. Phospholipids contain kinks that allow for more fluidity in the cell membrane while fats and oils are saturated fats that are closely packed together.

What is an organelle? How do they increase the complexity of eukaryotic cells?

An organelle is any one of several compartments in eukaryotes that divide the cell contents into smaller spaces specialized for different functions

What structures in eukaryotic cells distinguish them from prokaryotic cells? What structures in eukaryotic cells actually resemble prokaryotic cells?

Eukaryotic cells have a nucleus and membrane-bound organelles, while prokaryotic cells don't.

What causes some proteins to be embedded in a cell membrane?

Most integral proteins contain residues with hydrophobic side chains that interact with fatty acyl groups of the membrane phospholipids, thus anchoring the protein to the membrane

What functions are served by each of these organelles?

Nucleus: control center; contains DNA, bound by double membrane Nucleolus: dense structure inside nucleus where ribosome synthesis occurs Ribosome: site of protein synthesis, not bound by membrane Rough ER: ER with ribosomes bound to it; site of membrane protein(ex. channels) or secreted protein synthesis Smooth ER: system of membranes and tubes that transports substances around the cell new lipids are generated, creates cholesterol Golgi apparatus: sorts and packages proteins made by ribosomes on ER Lysosome: digests foregin substances and worn out organelles Vesicle: transports nutrients around the cell Mitochondria:functions in cellular respiration; produces ATP for the cell, bound by a double membrane Chloroplast(plant cells): site of photosynthesis

What is the difference between osmosis and diffusion?

Osmosis is when the solvent molecules pass the semipermeable membrane to get to the more concentrated solution. Diffusion is the movement of molecules from a higher concentration to a lower concentration

How are cell membranes formed?

Phospholipids spontaneously form a bilayer structure where polar head is on outside to interact with water and nonpolar tails come together on the inside away from water.

What is the relationship between concentration gradient across a membrane and the rate and diffusion of molecules across that membrane?

Since the net movement of diffusing moleculesdepends on the concentration gradient, the rate of diffusion is directly proportional to the concentration gradient (dC/dx) across the membrane.

What kinds of molecules can diffuse directly across a cell membrane?

Small nonpolar molecules, such as O2 and CO2, are soluble in the lipid bilayer and therefore can readily cross cell membranes. Small uncharged polar molecules, such as H2O, also can diffuse through membranes.

How is the fluidity or rigidity of the cell membrane controlled?

The presence of cholesterol at a high temperature in the cell membrane makes it more rigid. If saturated fatty acids are compressed by decreasing temperatures, they press in on each other, making a dense and fairly rigid membrane. If unsaturated fatty acids are compressed, the "kinks" in their tails push adjacent phospholipid molecules away, which helps maintain fluidity in the membrane.

What is meant by the endomembrane system? Which organelles are part of this system and how are they related?

The system of interconnected organelles is called the endomembrane system. It includes the nuclear envelope, endoplasmic reticulum, golgi apparatus, lysosomes, plasma membrane and the vesicles that move between them. This system makes two compartments within a cell: the area within these organelles and the area outside of these organelles. This separation allows specific functions to take place within the spaces defined by the membranes and also within the membrane itself.

How can cells use active transport to keep osmosis from bursting the cell?

To regulate the salt concentration in/out of the cell, active transport can force molecules against their concentration gradient and prevent the cell from shrinking or bloating.

Could you describe whether each of the following molecules crosses the cell actively or passively?

a. A small lipid molecule- Passively b. An ion passing through a transport protein down its concentration gradient- Passively (should this be active since it's an ion?) c. Glucose- Actively d. An ion moving into the cell against the concentration gradient-Actively e. Water moving into the cell by osmosis-Passively

Which features are found in all cells and which are unique to plant, animal, or bacterial cells? (Consider things like cell walls, membranes, DNA, proteins, ribosomes, ER, mitochondria, etc.)

all- plasma membrane plant- cell wall, chloroplasts plant/animal- nucleus and organelles