Biochemistry

Question 1

How do electrons exist?

Answer 1

In a probability density - they belong in a certain possibility within

Question 2

How are shells and sub shells arranged?

Answer 2

By energy level

Question 3

Why are electrons added to 4s before 3d?

Answer 3

4s is at a lower energy level than 3d

Question 4

What causes electron shielding and what does electron shielding cause?

Answer 4

Filled up shells and sub shells - it weakens the nuclear charge to outer electrons

Question 5

Definition of a mole?

Answer 5

Amount of any substance that contains as many elementary entities as there are atoms in 12 grams of pure carbon-12

Question 6

What does periodicity refer to?

Answer 6

Patterns of physical and chemical properties within the periodic table

Question 7

What happens to the atomic radius as you go down a group?

Answer 7

Down a group - atomic radius increases

Question 8

What happens to the atomic radius when you go across a period and why?

Answer 8

Atomic radius decreases. This is because as you go across a period, more electrons are being added to the sub shells but they’re not increasing in energy levels so theres no extra shielding. However, you’re adding more protons which increases the nuclear charge and draws more electrons closer to the nucleus

Question 9

Definition of ionisation energy?

Answer 9

The energy required to remove one mole of electrons from one mole of gaseous atoms

Question 10

Why do noble gases have a high ionisation energy?

Answer 10

Have a full outer shell of electrons

Question 11

Why do group one elements have a low ionisation energy?

Answer 11

Theres only one electron in their outermost shell so theres low level of nuclear charge

Question 12

What gives a higher level of stability in an atom?

Answer 12

When a sub shell if filled or half filled

Question 13

Across a period, what is the general pattern of ionisation energy?

Answer 13

Increases

Question 14

Down a group, what is the general pattern of ionisation energy?

Answer 14

Decreases

Question 15

What is electronegativity?

Answer 15

A measure of the tendency of an atom to attract a pair of bonding electrons via Pauling scale. Fluorine is most electronegative (4.0) and Cs and Fr are least electronegative (0.7)

Question 16

Across a period, what is the general patter of electronegativity and why?

Answer 16

Electronegativity increases across a period as there is a lower atomic radius so the nuclear charge exerts a higher level of control over outer shells of electrons

Question 17

Down a group, what is the general patter of electronegativity and why?

Answer 17

Electronegativity decreases down a group as theres increased levels of shielding due to more filled shells so less attractive forces from the nucleus to pull outer electrons closer

Question 18

What is orbital hybridisation?

Answer 18

A theory/model that explains how elements form bonds when their electron structure is unfavourable - carbon is the biggest example of this

Question 19

Why is carbon a good example of orbital hybridisation?

Answer 19

There are only 2 electrons in carbons outer shell but it needs 4 to share - it hybridises the outer electrons (making one large sub shell out of two) so 2p becomes 2sp^3. Each become half filled. The structure changes too and electrons spread as far as possible (trigonal pyramidal - 109.47º)

Question 20

What is an ionic bond?

Answer 20

A chemical link between two oppositely charged ions, caused by the electrostatic force between oppositely charged ions in an ionic compound - always between metals and non-metals

Question 21

Properties of ionic compounds

Answer 21

• High melting and boiling points

- Water soluble

Question 22

What is a covalent bond?

Answer 22

A chemical link formed when two atoms share electron pairs - always between non-metals

Question 23

How are carbon-carbon sigma bonds formed?

Answer 23

Through sp^3 hybridisation

Question 24

How are carbon-carbon double bonds (pi bonds) formed?

Answer 24

Formed through sp^2 hybridisation using a sigma and pi bond. There’s an electron dense area surround the bonds

Question 25

Properties of covalent compounds?

Answer 25

-Lower melting and boiling points due to fewer intermolecular interactions, though there are strong intramolecular. Water has a slightly higher mpt and bpt due to intramolecular interactions (hydrogen bonds)

Question 26

What is co-ordinate bonding?

Answer 26

A co-ordinate covalent bond is a covalent link between two atoms, but in which both of the shared electrons comes from one of the bonding partners. Frequently involves O, N, Cl due to unpaired/lone electrons Most commonly found in transition metals

Question 27

What is hydrogen bonding?

Answer 27

A weak electrostatic attraction that forms between polar molecules and occurs when. hydrogen atom bonds to.a highly electronegative atom (O-H, F-H, N-H, Cl-H)

Question 28

Strength of hydrogen bonds

Answer 28

A hydrogen bond individually is very weak but if theres lots of them together in a structure, they're strong e.g. in proteins, peptide bonds hold amino acids together but hydrogen bonds join amino acids together at different points

Question 29

Definition of stereoisomer?

Answer 29

A form of isomerism in which molecules have the same molecular formula and sequence of bonded atoms but differ in 3D orientations of their atoms in space

Question 30

What are the 2 enantiomers of stereoisomers and which is in all human proteins?

Answer 30

L and D | L-amino acids is in all proteins in humans

Question 31

What are the 5 classifications of amino acids by R group?

Answer 31

1) Non-polar, aliphatic R groups 2) Polar, uncharged R groups 3) Aromatic R groups 4) Positively charged R groups 5) Negatively charged R groups

Question 32

Explain non-polar, aliphatic classification and some amino acid examples

Answer 32

Non-polar - Side chains cannot form hydrogen bonds/non-soluble in water (hydrophobic) Aliphatic - A chain of carbons and hydrogens Glycine - Simplest and only non-chiral amino acid as it doesn't have 4 different groups Proline - an IMINO acid, side chain forms a bond with nitrogen in amine group Methionine - contains unreactive sulphur

Question 33

Explain polar, uncharged classification and some amino acid examples.

Answer 33

Soluble in water, contains atoms that can form hydrogen bonds Serine and threonine - contain hydroxyl groups that can be phosphorylated to control the activity of metabolic pathways Cysteine - SH which forms hydrogen bonds and another amino acid can protect from oxygen free radicals (oxidative stress)

Question 34

Explain aromatic classification

Answer 34

Benzene ring - relatively big - highly hydrophobic - tend to be found in the centre of water soluble proteins/outside of proteins in membranes (intact with hydrophobic fatty acids) -Only 3 amino acids (proteinogenic) that can absorb UV light

Question 35

Explain positively charged classification and AA examples

Answer 35

- Referred to as basic amino acids (lysine and arginine) | - Side chains are positively charged - electrostatic interactions (salt bridges)

Question 36

Explain negatively charged classification and AA examples

Answer 36

- Each has COO- in side chain (aspartate and glutamate) - Can form electrostatic interaction with positively charged R groups - Can interact with metal ions

Question 37

In humans, which amino acid is found at highest levels in the blood in its free form (not part of protein)?

Answer 37

Glutamine

Question 38

Which pathways are important for amino acid synthesis?

Answer 38

Glycolysis, pentose phosphate pathway and TCA cycle (Krebs cycle)

Question 39

What are essential amino acids?

Answer 39

We can't make them, they have to come through the diet

Question 40

What are non-essential amino acids?

Answer 40

We can make using one of more essential amino acid

Question 41

What are conditionally essential amino acids?

Answer 41

Not required in healthy adults but are in young people and some diseased people. Its essential for them because they can't generate enough themselves

Question 42

Whats an electrophile?

Answer 42

reactive molecule thats attracted to areas rich in electrons - usually something with a negative charge or double bond (positively charged ions)

Question 43

Features of alkanes

Answer 43

- Non-polar, few intermolecular bonds - Small hydrocarbons have very low mpt and bpt, tend to be gases at room temp - As chain increases, carbon chains wrap around each other and interacting, increasing bpt

Question 44

Features of alkenes

Answer 44

-Unsaturated, have at least one pi bond -More reactive than alkanes -Less flexible than alkanes -Found in unsaturated fatty acids -Low mpt bpt Non polar