FLC: intro to the living cell

Question 1

What are proteins?

Answer 1

Polymers of amino acids

Question 2

What is the structure of amino acids?

Answer 2

-Amine group(NH3+)
-Carboxyl group(COO-)
-R group(side chain)
-Central Carbon atom
-Hydrogen

Question 3

Structure of amino acid at low pH

Answer 3

-Amine group(NH3+)
-Carboxyl group(COOH)
-R group(side chain)
-Central Carbon atom
-Hydrogen

Question 4

Structure of amino acid at intermediate pH

Answer 4

Zwitterion at intermediate pH
-Amine group(NH3+)
-Carboxyl group(COO-)
-R group(side chain)
-Central Carbon atom
-Hydrogen

Question 5

Structure of amino acid at high pH

Answer 5

-Amine group(NH2)
-Carboxyl group(COO-)
-R group(side chain)
-Central Carbon atom
-Hydrogen atom

Question 6

What are proteins polymers of?

Answer 6

Polymers of 20 different amino acids

Question 7

How is a peptide bond formed between amino acids?

Answer 7

Formation of a peptide bond by condensation

Question 8

What is the sequence of amino acids called and what are the terminal ends called?

Answer 8

The sequence of amino acids is called
the primary structure of a protein
-Amino-terminal end
-Carboxyl-terminal end

Question 9

What are the 4 levels of protein structure and what is included in them?

Answer 9

Primary structure
-Amino acid residues
Secondary structure
-Alpha helix
Tertiary structure
-Polypeptide chain
Quaternary structure
-Assembled subunits

Question 10

What are amino acids joined by in the primary structure?

Answer 10

Amino acids are joined by
strong covalent bonds in
the primary structure.

Question 11

What are higher orders of protein structures dependant on?

Answer 11

Higher orders of structure
are mostly dependent on
weak bonds (ionic,
hydrogen and hydrophobic)
but may be stabilized by
covalent bonds.

Question 12

What is the secondary structure of proteins made by?

Answer 12

-Alpha helices
-Beta pleated sheets

Question 13

What are beta pleated sheets?

Answer 13

Beta-pleated sheet is a series of anti-parallel chains of covalently linked amino acids with adjacent chains linked by hydrogen bonds

Question 14

What is alpha helix and what is it stabilised by?

Answer 14

Alpha helix is a motif and right handed helix stabilized by H-bonds between the amide H of one amino acid and the carbonyl group 4 residues along the chain.

Question 15

What do side chains in alpha helix do and what can these residues be?

Answer 15

Side chains protrude
from sides of the helix.
In some cases residues
are hydrophilic on one
side of the helix and are
hydrophobic on the
other.

Question 16

What happens to helices and sheets in the tertiary structure?

Answer 16

Helices and sheets are folded up into more densely packed globular structures.

Question 17

What does formation of tertiary structures depend on?

Answer 17

Formation of these structures depends on weak chemical bonds between side chains.

Question 18

What may structures be stabilised with in tertiary structure?

Answer 18

The structures may be stabilized by covalent disulfide bonds between cysteine residues.

Question 19

What happens to form a quaternary structure?

Answer 19

In some cases, ≥2 folded polypeptides may be combined to form the mature protein.

Question 20

What is the quaternary structure of haemoglibin?

Answer 20

hemoglobin containing 4 polypeptides + 4 heme groups

Question 21

What are examples of non-covalent interactions in proteins

Answer 21

-Ionic bonds
-Hydrogen bonds
-Van der Waals attractions

Question 22

What is the stabilisation of 3 degree and 4 degree structure?

Answer 22

-Disulfide bonds
-Sulfhydryl side chain of cysteine:
May Crosslink a single polypeptide
chain (3° structure) or two separate
molecules (4° Structure).

Question 23

How are protein structures determined?

Answer 23

Protein structure may be determined in various ways, principally
X-ray crystallography and nuclear magnetic resonance (NMR)
spectroscopy.

Question 24

What shape do water soluble proteins tend to be?

Answer 24

Water soluble proteins are often globular in shape:
* Hydrophilic residues mostly on the external surface.
* Hydrophobic residues usually buried inside the protein.

Question 25

How are membrane proteins organised?

Answer 25

• Membrane spanning regions have externally located
  hydrophobic residues that interact with the membrane lipids.
• They may have hydrophilic central channels.

Question 26

What helix does collagen have?

Answer 26

Collagen has a triple helix (NOT an alpha helix).

Question 27

How may collagen fibres assemble?

Answer 27

Collagen molecules may assemble into long fibres or sheets.

Question 28

What does the primary sequence of the protein determine?

Answer 28

The primary sequence determines the folding of the polypeptide into the
functional protein structure.

Question 29

What is sickle cell anaemia caused by?

Answer 29

Caused by a mutation that changes a single amino acid in the beta chain of haemoglobin:
Glu (negative) is replaced by Val (hydrophobic ) at position 6.

Question 30

What does mutant haemoglobin(HbS) form in the deoxygenated state?

Answer 30

In the deoxygenated state, the mutant haemoglobin (HbS) forms insoluble fibres (the
HbS molecules stick together).