Proteins Flashcards
(131 cards)
1
Q
What are globular proteins?
A
Proteins formed by compact amino acid chains, then folded into intricate chains that resemble spheres
2
Q
Are globular proteins soluble or insoluble?
A
Soluble
3
Q
Give an example of a globular protein
A
Insulin
4
Q
Where is insulin produced?
A
In the pancreas
5
Q
What does insulin do?
A
It aids the bodies ability to regulate energy and metabolise sugars
6
Q
What does insulin illustrate?
A
A proteins ability to act as a biological messenger
7
Q
What can proteins act as?
A
Biological transport mechanisms, biological messengers and they can play a role in the structure of animal cells
8
Q
What are conjugated proteins?
A
Proteins that function in interaction with other chemical groups
9
Q
How are conjugated proteins attached?
A
By weak covalent bonds
10
Q
Are conjugated proteins soluble or insoluble in water?
A
Soluble in water
11
Q
What are proteins?
A
Long chains of amino acids
12
Q
Give an example of a conjugated protein
A
Haemoglobin and catalase
13
Q
What are fibrous proteins?
A
A protein with an elongated shape, forming a rod or wire like shape
14
Q
What do fibrous proteins provide?
A
Structural support for cells and tissues
15
Q
Give examples of fibrous proteins
A
Keratin, elastin and collagen
16
Q
Are fibrous proteins insoluble or soluble in water?
A
Insoluble
17
Q
What enzymes break down proteins?
A
Protease enzymes
18
Q
What is a prosthetic group?
A
A non-protein component in globular proteins
19
Q
What are proteins without a prosthetic group called?
A
Simple proteins
20
Q
What is formed when a lipid and a protein combine?
A
A lipoprotein
21
Q
What is formed when a carbohydrate combines with a protein?
A
A glycoprotein
22
Q
What is a cofactor?
A
A prosthetic group formed by metal ions and vitamins
23
Q
Give an example of a prosthetic group
A
A haem group which contains an iron ion
24
Q
What contains a haem group?
A
Catalase and haemoglobin
25
What bonds form between amino acids?
Peptide bonds
26
How does the protease enzyme denature the protein?
It breaks the bonds, altering the structure, it first breaks the hydrogen bonds, then the ionic bonds and then the disulphide bridges
27
What changes in the structure of amino acids?
The R group, but all amino acids have the same general formula
28
What are the four structures of proteins?
- primary structure
- secondary structure
- tertiary structure
- quarternary structure
29
How many naturally occurring amino acids are there?
20, each with there own R group
30
How is a polypeptide chain formed?
Condensation reactions when amino acids are added to a dipeptide
31
How many polypeptides does one protein consist of?
One polypeptide chain
32
What is polymerisation?
The process by which condensation reactions take place to form a polypeptide from amino acids
33
What are the types of proteins?
- Structural
- Catalytic
- Signalling
- Immunological
34
What are structural proteins?
They are the main component of body tissues such as muscles, skin, hair and ligaments
35
What are catalytic enzymes?
All enzymes are proteins catalysing many biochemical reactions
36
What are signalling proteins?
Hormones and receptors (many of these are proteins)
37
What are immunological proteins?
Antibodies
38
Where is a disulphide bridge formed?
Between two cystine amino acids
39
What does the primary structure look like?
A long chain of amino acids joined by polypeptide bonds
40
What does the primary structure of the protein determine?
It’s shape and function
41
What are the two secondary structures?
Alpha helix and beta pleated
42
What bonds do the secondary structure contain?
Weak hydrogen bonds
43
How are weak hydrogen bonds formed?
Between the positive charge on the hydrogen and the negative charge on the oxygen
44
What do the hydrogen bonds cause in the secondary structure?
The long polypeptide chains to twist into a 3D helix
45
What is the tertiary structure?
The 3D protein structure which is further folded and twisted to give it a more complex 3D structure
46
How in the tertiary structure maintained?
- Disulfide bonds
- Ionic bonds
- hydrogen bonds
47
What are disulphide bonds?
Bridges formed between cystine, they are strong and difficult to break
48
What are ionic bonds?
Bonds formed between carboxyl and amino groups that are not involved in the formation of peptide bonds, they are weaker than disulphide bridges
49
What are hydrogen bonds like?
Hey are numerous but they are weak and easily broken
50
What is the bond between two amino acids?
A dipeptide bond
51
How are peptide bonds formed?
The joining of amino acids by a condensation reaction
52
What are the four groups in an amino acids?
- Amino group
- Carboxyl group
- Hydrogen atom
- R side group
53
Where does the peptide bond form?
Between the carbon atom of one amino acid and the nitrogen atom of another
54
Where is the water produced in the condensation reaction
The OH from the carboxyl group and the H from the amino group
55
What is the process of the formation of a polypeptide
Polymerisation
56
Why can hydrogen bonds form between proteins?
The NH group has an overall positive charge whilst the O has an overall negative charge so they are therefore polar
57
What is the test for proteins?
The biuret test
58
What does the biuret test detect?
Peptide bonds
59
How do you carry out the biuret test?
- Place a sample of the solution in a test tube and add equal volume of sodium hydroxide solution at room temperature
- Add a few drops of very dilute (0.05%) copper (II) sulfate solution and mix gently
60
What result identifies a protein?
Purple coloration
61
What is the negative result?
The solution remains blue
62
What is the primary structure of collagen?
An unbranded polypeptide chain
63
What is the secondary structure of collagen?
Very tightly wound
64
What is the tertiary structure of collagen?
The chain is twisted into a second helix
65
What is the quarternary structure of collagen?
Three polypeptide chains would together
66
Where is collagen found?
Tendons
67
How do autotrophic green plants produce amino acidsz?
As a product of photosynthesis
68
How do heterotrophic organisms gain their amino acids?
From plants through food chains
69
What do simple proteins have in their structure?
Only amino acids
70
Give examples of simple proteins
Albumins, globulins and scleroproteins
71
What do conjugated proteins contain?
Amino acids and some other type of chemical molecule
72
What is the prosthetic group in a a nucleoprotein?
Nucleic acids
73
What is the prosthetic group in a phosphoprotein?
Phosphoric acid
74
What is the prosthetic group in lipoprotein?
A lipid
75
What does haemoglobin contain?
4 poly peptide chains each of which has a porphyrin ring which contains the iron ion
76
What does pH affect?
How the amino acids and proteins ionise
77
How does the carboxylic acid group ionise?
RCOOH <=> RCOO- + H+
78
How does the amino group ionise?
RNH2 + H+ <=> RNH3+
79
How does a high pH effect the ionisation of the carboxylic acid?
The reaction will be pushed to the left
80
How does a high pH effect the ionisation of the amine group?
The reaction will be pushed to the right
81
In a high pH environment with the amino acids be positively or negatively charged?
The amino acids will predominantly be positively charged cations
82
How does a low pH effect the ionisation of the carboxylic acid?
The reaction will be pushed to the right
83
How does a low pH effect the ionisation of the amine group?
The reaction will be pushed to the left
84
In a low pH environment with the amino acids be positively or negatively charged?
The amino acids will predominantly be negatively charged anions
85
When will a zwitterion form?
When there is an intermediate hydrogen ion concentration where the forward and the backwards rates of reaction for the ionisation of the carboxylic acid and the ionisation of the amine group are equal
86
Why will a zwitterion form?
Because the amino acid will carry 50% of the amine groups uncharged and 50% of the amine groups charged and will carry 50% of the carboxylic acid group charged and 50% of the carboxylic acid group uncharged
87
What will pH of zwitterion formation dictate?
The isoelectric point
88
Why do different enzymes have different optimum pH’s?
Because the isoelectric point is different for each specific amino acid or protein
89
What is the iso-electric point?
The pH at which the amino acids or protein carry no net charge/ carry equal amounts of negative and positive charges
90
Will the charge on the active sites of an enzymes affect the capability of the enzyme to join with its specific substrate?
Yes, that’s why enzymes tend to work best at specific pH’s
91
How does pH affect solubility?
At the IEP opposite charges attract making protein molecules clump together and precipitate. At other pH’s the protein will only carry like charges which will repel molecules from each other which can increase the solubility.
92
What happens to proteins at extremes of pH
The protein molecules will carry huge numbers of like charges (as the ionisations of the amine groups and the carboxylic acid groups will go almost to completion). These charges may exert a large repulsive force which breaks apart the hydrogen and ionic bonds holding the 3D structure together. Therefore the 3D structure therefore breaks apart and the protein is denatured.
93
What is denaturation?
The loss of function of a protein caused by a loss of structure
94
As well as ph what is another agent of denaturation?
Heat
95
How does heat cause denaturation
It can disrupt the hydrogen and ionic bonds therefore causing the 3D structure to unravel.
96
At what temperature do most proteins denature?
45 degrees
97
Which bonds in proteins can withstand the higher temperatures?
Sulphur bonds therefore proteins containing the most sulphur bonds can withstand the highest of temperatures
98
What are the functions of proteins?
- Structural proteins
- Enzymes
- Hormones
- Contractile proteins
- Storage proteins
- Transport proteins
- Protective proteins
- Buffers
- Osmotic proteins
- Toxins
99
Give examples of structural proteins
- Collagen
- Elastin
- Keratin
- Lipoproteins
- Fibroin
- Sclerotin
- Mucoproteins
100
Give examples of enzymes
- hydrolases such as; amylase, proteases and lipases used in digestion
- oxido-reductases such as the dehydrogenase used in the metabolic cycle and ligases
101
Give examples of hormones
- somatotropin
- pituitary growth hormone
- insulin
102
Give examples of contractile proteins
- actin
- myosin
- dynein
103
Give examples of storage proteins
- ovalbumin
- casein
- lactalbumins
- glutelins
- gliadins
- ferritin
104
Give examples of transport proteins
- haemoglobin
- myoglobin
- plasma albumin
- transferritin
- binding globulins
105
Give examples of protective proteins
- thrombin
- fibrinogen
- antibodies
106
Give an example of a buffer
Haemoglobin
107
Give an example of an osmotic protein
Plasma albumin
108
Give examples of toxins
- phospholipase
- clostridium tetani
- clostridium botulinum
- diphtheria
- ricin
109
What is the function of ligases?
They enable molecules to be bond together using energy from ATP
110
Where is actin and myosin found?
Muscles
111
What does dynein make up?
The structure of cilia and flagella
112
Why can’t amino acids be stored as just amino acids?
Because of the toxic amine groups
113
How do you store amino acids?
As proteins
114
What is ovalbumin, casein and lactalbumin?
Milk proteins
115
What are glutelins and gliadins?
Cereal seed proteins
116
What is ferritin?
A protein that binds up iron and stores it in the spleen, liver and red bone marrow
117
How do transport proteins work?
By binding onto and releasing insoluble or inadequately soluble substances so they can be transported through the body
118
What does haemoglobin do?
Transports oxygen in vertebrate blood
119
What does myoglobin do?
Transports oxygen in muscles
120
What does plasma albumin do?
Transports fatty acids in the blood
121
What does transferritin do?
Transports iron through blood to the iron storage sites
122
What do binding globulins do?
Transports insoluble thyroid hormones through the blood
123
What are thrombin and fibrinogen?
Blood clotting factors which reduce bleeding during injury
124
What are antibodies?
Proteins that react with antigens to neutralise them therefore giving protection against disease
125
What is a buffer?
A substance that is resistant to changes in pH
126
How does haemoglobin work as a buffer?
It reacts with hydrogen ions to form reduced haemoglobin which can buffer blood between 7.2 and 7.6
127
How does plasma albumin work?
It maintains blood volume by maintaining the water level in blood plasma. Cell sap has the same role in plants
128
What are phospholipases?
Enzymes found in snake venom which destroy cell membranes
129
What are clostridium tetani, clostridium botulinum and diphtheria?
Bacteria that release toxic chemicals, harmful to humans
130
What is ricin?
A toxic chemical that can cause jaundice
131
What elements are present in proteins?
Carbon, hydrogen, oxygen and nitrogen are present (without including elements present in R groups)
