Unit 3: Membrane Structure and Function
When a carbohydrate chain is attached to a phospholipid, what is the structure called?
A glycolipid
When a carbohydrate chain is attached to a protein, what is the structure called?
A glycoprotein
How is ATP used in active transport?
ATP acts as one of the "keys" for the protein, helping to "unlock" the channel. Energy is used to change the shape of the protein and open the channel.
Why does active transport require energy input by the cell?
Active transport requires energy input by the cell because it lowers the "activation energy" of a cell→moves molecules up/against concentration gradient using energy
Why does active transport start off with such a high initial rate compared to diffusion and facilitated diffusion?
Because active transport uses a supply of energy→does not depend on a concentration gradient
Why would the rate of transport with facilitated diffusion level off as the concentration increases, while the rate of transport of diffusion continue to increase at a steady rate?
Because facilitated diffusion relies on proteins, limiting the rate of diffusion. Even if the concentration continues to increase, the number of protein channels will limit the rate of facilitated diffusion.
How is the use of a gated channel facilitated diffusion?
Larger molecules, like glucose, need the help of the hormone and the protein in order to cross the protein channel.
Is a substance moved along (down) a cencentration gradient in active transport?
No, substances move up a concentration gradient in active transport (low→high concentration).
What two major types of biological molecules compose the majority of the cell membrane?
Phospholipids and proteins
Which molecules are able to pass through the semi-permeable membrane?
Small molecules are able to pass through the semi-permeable membrane because they can fit between the gaps between the phospholipids *nonpolar molecules (not charged)*
What is the difference between the position of the surface proteins and the membrane spanning proteins?
Surface proteins never reach across the membrane, but the membrane-spanning proteins do
What is the gap between the membrane-spanning proteins called?
The gated channel
Explain in detail what happens to allow glucose to pass through the membrane-spanning protein.
The hormone attaches to the protein at the hormone binding site, causing the gated channel to open. *by attaching to the protein, the hormone caused it to change shape*
The "tails" of phospholipids are nonpolar; therefore, they do not readily interact with charged particles such as ions. How can this explain why facilitated diffusion is necessary for the transport of ions such as Na+ and K+ across the cell membrane? (In other words, why would these ions not cross by simple diffusion?)
The ions would not cross by simple diffusion because they are polar (charged), so facilitated diffusion is the only way for them to get across.
diffusion
The net movement of molecules from an area of *high* concentration to an area of *low* concentration. The molecules will continue to move along this *concentration gradient* until they reach *equilibrium*. Once equilibrium is reached, molecules will continue to move across a membrane *randomly*.
Which type of cell transport would be best to move substances into or out of the cell quickly?
active transport
Which type of transport would be best if the cell needs to respond to a sudden concentration gradient difference?
diffusion→the rate increases as the concentration difference increases
What type of molecules attach to the membrane-spanning proteins?
hormones
facilitated diffusion
molecules move along (down) a concentration gradient always involves channel (membrane-spanning) proteins moves ions like Na+ and K+ moves large molecules
diffusion
molecules move along (down) a concentration gradient molecules pass between the phospholipids moves small nonpolar and polar molecules
What type of transport are diffusion and facilitated diffusion?
passive transport
active transport
requires energy input by the cell moves molecules against (up) a concentration gradient always involves channel (membrane-spanning) proteins moves large molecules
