Biochemistry

Question 1

What determines the upper and lower limit of cellular dimensions?

Answer 1

1. The upper limit is set up by the rate of diffusion of solute molecules in aqueous systems.
2. The lower limit is given by the minimum number of each type of biomolecule required by the cells.

Question 2

What are the chiral centers?

Answer 2

Asymmetric carbons

Question 3

How many stereoisomers can a molecule with n carbon atoms have?

Answer 3

2^n

Question 4

What are enantiomers and diastereosomers?

Answer 4

1. Enantiomers are called 2 stereoisomers that are mirror images of each other.
2. Diastereomers are stereoisomers that are not mirror images of each other.

Question 5

When a system is defined as isolated, closed or open?

Answer 5

1. Isolated –> Exchanges neither energy nor matter with its surroundings
2. Closed –> Exchanges energy but not matter with its surroundings
3. Open –> Exchanges both energy and matter with its surroundings

Question 6

What is the definition of entropy (S)?

Answer 6

It is the expression of the randomness of the components of a chemical system and, conventionally, it has a positive value

Question 7

How can the free energy (G) of a closed system be defined?

Answer 7

G = H - TS
H: enthalpy, number and kind of bonds
S: entropy
T: absolute temperature (K)

Question 8

When a reaction is exoergonic and when is it endoergonic?

Answer 8

An exoergonic reaction liberates free energy (negative deltaG), while an endorgonic reaction requires energy (positive deltaG).

Question 9

How can the standard free energy change (deltaG) be realted to the equilibrium constant?

Answer 9

ΔG = ΔG0 + RT ln ( [C^c][D^d] / [A^a][B^b])

Question 10

What is the activation energy?

Answer 10

Is the difference in energy between the reactant at its ground state and the reactant at its transitional state

Question 11

Which are the definitions of catabolism and anabolism?

Answer 11

1. Catabolism is the set of degrading exoergonic reactions that transform organic nutrients into simple end products in order to extract chemical energy and convert it into a form useful to the cell.
2. Anabolism is the set of endoergonic reeactions that convert small molecules into complex molecules (proteins, nucleic acids,…)

Question 12

What does it mean that a molecule of water has an electrive diapole moment?

Answer 12

It means that there is an unequal distribution of electron density, therefore polarity

Question 13

What is the hydrophobic effect and why is it a favourable reaction?

Answer 13

It is the formation of hydrophobic interactions between two non-polar molecules when these are added to water and is considered a favourable reaction because it allows the “trapped” H2O molecules to form H bonds between each other

Question 14

Which are the 2 more important biological buffers used in our body and where are they used?

Answer 14

1. The dihydrogen phosphate/phosphoric acid buffer is used to buffer the cytoplasm of cells.
2. The carbonic acid/bicarbonate ion buffer is used to buffer blood plasma.