3.2 cells Flashcards

Question

What is the purpose of proteins in the membrane

Answer 1

Functions of proteins in the membrane are to: Provide structural support Act as channels transporting water-soluble substances across the membrane Allow active transport across the membrane through carrier proteins Helps cells adhere together Act as receptors

Answer 2

Occur within the phospholipid bilayer of the cell-surface membrane. Add strength to the membranes. Very hydrophobic and therefore play an important role in preventing loss of water and dissolved ions from the cell. They also pull together the fatty acid tails of the phospholipid molecules, limiting their movement and that of other molecules but without making the membrane too rigid.

Answer 3

Functions in the membrane are to: Reduce lateral movement of other molecules including phospholipids Makes the membrane less fluid at high temperatures Prevents leakage of water and dissolved ions from the cell

Answer 4

Carbohydrate chains are attached to many extrinsic proteins on the outer surface of the cell membrane. Thee glycoproteins also act as cell-surface receptors, more specifically for hormones and neurotransmitters Functions of glycoproteins in the membrane are to: Act as recognition sites Helps cells to attach to one another and form tissues Allows cells to recognise one another, for example lymphocytes can recognise an organisms own cells

Answer 5

Made up of a carbohydrate covalently bonded with a lipid. The carbohydrate portion extends from the phospholipid bilayer into the receptor for specific chemicals

Answer 6

Functions in the membrane are to: Act as recognition sites Helps cells attach to one another and so form tissues Help maintain the stability of the membrane

Answer 7

Fluid- individual phospholipid can move relative to one another. This gives the membrane a flexible structure that is constantly changing in shape Mosaic- proteins embedded in the phospholipid bilayer vary in shape, size and pattern in the same way as stones or tiles of a mosaic. [ see physical flashcards for diagram]

Answer 8

``` Fluid mosaic model Phospholipids Globular proteins Outside is intrinsic Span membranes –intrinsic ```

Answer 9

Controls the movement of substances in and out of the cell. In general, most molecules do not freely diffuse across it because many are: Not soluble in lipids and therefore cannot pass through the phospholipid bilayer Too large to pass through the channels Of the same charge as the charge on protein channels and so, even if they are small enough to pass, they are repelled. Electrically charged/ are polar and therefore have difficulty passing through the non-polar hydrophobic tails in the phospholipid bilayer

Answer 10

Diffusion- net movement of molecules or ions from an area of higher concentration to one where their concentration is lower until it is evenly distributed All particles are constantly in motion due to kinetic energy . The motion is random, with no set pattern Particles are constantly bouncing off one another and other objects Particles that are concentrated together in a part of a closed vessel will distributed themselves evenly.

Answer 11

``` Factors affecting diffusion Large surface area Temperature Concentration difference Length of diffusion pathway ( shorter= faster diffusion) ```

Answer 12

As carbohydrates and proteins are being digested continuously, there are normally a greater concentration of glucose and amino acids within the ileum than in the blood. There is therefore a concentration gradient down which glucose moves by facilitated diffusion from being inside the ileum into the blood. Given that blood is being continuously being circulated by the heart, the glucose absorbed into it is continuously being removed by cells as they use it up during respiration. Helps maintains the concentration gradient between the ileum and the blood. This means the rate of movement by facilitated diffusion across epithelial cell-surface membranes is increased

Answer 13

1. Sodium ions are actively transported out of epithelial cells, by the sodium-potassium pump, into the blood. This takes place in 1 type of protein carrier molecule found in the cell-surface membrane of the epithelial cells 2. Maintains a much higher concentration of sodium ions in the lumen of the intestine than inside of the epithelial cells 3. Sodium ions diffuse into the epithelial cells down this concentration gradient through a different type of protein carrier( so-transport protein) into the cell surface membrane. As the sodium ions diffuse in through this 2nd carrier protein, they carry either amino acids or glucose into the cell 4. The glucose/amino acids pass into the blood plasma by facilitated diffusion

Answer 14

The passage of water from a region where it has a higher water potential to a region where it has a lower water potential through a selectively permeable membrane Water potential Measured in units of pressure, usually kiloPascals (kPa) Is the pressure created by water molecules. Under standard conditions of temp and water (25° and 100kPa ), water is said to have a water potential of 0.

Answer 15

Addition of a solute to pure water will lower its water potential Water potential of a solution must always be less than 0, that is, a negative value More solute that is added ( more concentrated), the lower (more negative) the water potential Water will move by osmosis from a region of higher ( less negative) water potential (e.g. -20kPa) to one of lower ( more negative) water potential ( e.g. -30kPa)

Answer 16

Where diffusion is helped Charged ions and polar molecules don’t diffuse easily due to the hydrophobic nature of the fatty acid tails of the phospholipids in the membranes Movement of these molecules is made easier ( facilitated) by transmembrane channels and carriers that span the membrane Is a passive process- relies on inbuilt motion (kinetic energy) of diffusing molecules

Answer 17

Occurs down a concentration gradient but occurs at specific points of the plasma membrane where there are special protein molecules : Protein channels Carrier proteins

Answer 18

Proteins form water-filled hydrophobic channels across a membrane Allows specific water-soluble ions to pass through Is selective and only opens in the presence of specific ions If these aren't present, it stays closed Ions bind with the protein, causing it to change the shape in a way that closes it to one side of the membrane and opens the other side.

Answer 19

Span the plasma membrane When a molecule such as glucose that is specific to the protein is present, it binds with the protein. This causes it to change shape in such a way that the molecule is released to the inside of the membrane. No external energy is needed for this. The molecule moves from a region where they are highly concentrated to one of lower concentrations, using only the kinetic energy of the molecules themselves.

Answer 20

The movement of molecules or ions into or out of a cell from a region of lower concentrated to a region of higher concentrations using ATP and carrier proteins.

Answer 21

ATP is used to: Directly move molecules Individually move molecules using a concentration gradient which has already been set up by (direct ) active transport. Known as co-transport.

Answer 22

Differs from passive forms of transport : Metabolic energy in the form of ATP is needed. Substances are moved against a concentration gradient, that is from a lower to higher concentration Carrier protein molecules which act as ‘pumps’ are involved. The process is very selective, with specific substances being transported.

Answer 23

Carrier proteins span the plasma membrane and bind to the molecule or ion to be transported on one side of it. The molecule or ion binds to receptor sites on the carrier protein On the side of the cell/organelle, ATP binds to the protein, causing it to split into ADP and Pi. As a result the protein molecule changes shape and opens to the opposite side of the membrane. The molecule or ion is then released to the other side of the membrane The phosphate molecule is released from the protein which causes the protein to revert to its original shape, ready for the process to be repeated, the Pi then recombines with ADP to form ATP during respiration