Midcourse Test pt 2 Flashcards
Q11 c) i) (read context ad see graph) explain & give reasons for the shape of the curve shown in Fig 3.4 (3 marks)
At low substrate concentrations, man of the enzyme active sites are empty
as more substrate is added, the rate of reaction increases because more enzyme-substrate complexes are formed
At high substrate concentrations, the curve plateaus because more of the active sites are being used
Q 11 3) 11) use Fig 3.4 to calculate the value of the Michaelis-Menten constant (Km) for the reaction between catechol oxidase and catechol
0.21 mol dm^-3
How do you work out Michaelis-Menten constant?
1/2 Vmax
Q11 iii) State what these km values indicate about the relationship between the enzyme and the 2 substrates
The enzyme has a higher affinity for methylcatechol
Q 12 ( look at Fig) why doesn’t hormone S need to pass through a transport protein to enter the cytoplasm of the target cell? 2
Hormone S can pass through the hydrophobic core of the bilayer
because they are lipid-soluble
The target cell can respond to other cell signalling molecules in addition to hormone
S. The cell has receptors in the cell surface membrane, in the cytoplasm and in the
nucleus.
Explain why hormone S binds only with receptor R in the cytoplasm and not with the
other receptors shown in Fig. 12.1
The hormone S is complementary in shape to receptor R, but not to the other receptors
Name the structure through which the hormone‑receptor complex enters the
nucleus.
Nuclear pore
Q 12 name structure G
a ribosome
Cell signalling by hormone S results in the production of a functioning globular
protein molecule composed of three identical polypeptide chains.
After the synthesis of these polypeptides, changes need to occur to form the
functioning globular protein molecule.
Outline the changes that need to occur to form the functioning globular protein
molecule. 5
The secondary structure must be formed from hydrogen bonding between 2 polar groups
resulting in alpha helices and beta pleated sheets
Then the tertiary structure must be formed from bonding (e.g. hydrogen bonds) between R-groups
This causes the chain to coil
lastly the quaternary structure can form as a result of protein chains being packed together
What are the bonds in tertiary structure? 4
Hydrogen, ionic, disulphide, hydrophobic interactions
Describe the differences in structure and function between the Rough Endoplasmic Reticulum (RER) and the Smooth Endoplasmic Reticulum (SER) 5
Rough endoplasmic reticulum is covered in ribosomes
and is used to produce proteins
Smooth endoplasmic reticulum lacks ribosomes
and is used to form lipids and steroids
or as a storage site for calcium ions
Describe the structure of a phospholipid molecule 3
They have 2 hydrophobic fatty acid tails
attached to a hydrophobic glycerol head
One tail is shorter than the other
Describe the features, other than the presence of Golgi vesicles, that would help you identify a Golgi body in a transmission electron micrograph of another area of the same liver cell. 2
The Golgi body is made of cisternae
which look like flattened sacs that bulge at the ends
Some Golgi vesicles contain secretory proteins for release from the cell.Describe the sequence of events that occurs following the packaging of a secretory protein into a Golgi vesicle to its release from the cell 2
The vesicle travels to and fuses with the cell surface membrane,
before leaving the cell through exocytosis
What is exocytosis 3
the process where the contents of a cell vacuole
are released outside the cell
through fusion of the vacuole membrane with the cell membrane
