Biological Molecules Flashcards
1
Q
What is a monomer?
A
The small units from which larger molecules are made
2
Q
What are polymers?
A
Molecules made from a large number of monomers joined together
3
Q
Give three examples of monomers
A
Monosaccharides, amino acids, nucleotides
4
Q
What is a condensation reaction?
A
A reaction joining together two molecules with the formation of a chemical bond, involving the elimination of a molecule of water
5
Q
What is a hydrolysis reaction?
A
A reaction breaking the chemical bond between two molecules involving the use of a water molecule
6
Q
What uses do carbohydrates have?
A
Carbohydrates can be respiratory substrates and acting as structural components in cell walls and plasma membranes
7
Q
What uses do lipids have?
A
Lipids are a major component of the bilayer of plasma membranes, they’re respiratory substrates and form some hormones.
8
Q
What uses do proteins have?
A
Proteins form many cell structures. They are also important as enzymes, chemical messengers and components of the blood.
9
Q
What uses do nucleic acids have?
A
Nucleic acids carry the genetic code for the production of proteins. The genetic code is common to viruses and to all living organisms, providing evidence for evolution
10
Q
What are monosaccharides?
A
The monomers from which larger carbohydrates are made.
11
Q
Name 3 monosaccharides
A
Glucose, fructose, galactose
12
Q
What is the bond formed between two monosaccharides in a condensation reaction?
A
A glycosidic bond
13
Q
What are the monomers that make maltose?
A
Two glucose monomers
14
Q
What are the monomers that make up sucrose?
A
Glucose and fructose
15
Q
What are the monomers that make up lactose?
A
Glucose and galactose
16
Q
What are the two isomers of glucose and how do they differ?
A
Alpha glucose and beta glucose.
They differ by the positions of the OH groups
17
Q
What are glycogen and starch polysaccharides formed from?
A
The condensation of alpha glucose monomers
18
Q
What is cellulose formed from?
A
The condensation of beta glucose monomers
19
Q
What is starch made of?
A
Two glucose polymers: amylose and amylopectin.
20
Q
What is amylose?
A
Long, unbranched chains of glucose with 1,4-glycosidic bonding
21
Q
What is amylopectin?
A
Long, highly branched chains of glucose with 1,4-glycosidic bonds and 1,6-branching
22
Q
What is glycogen’s function?
A
Glycogen is the main storage polysaccharide in animal cells.
23
Q
What is glycogen?
A
Long, branched chains of glucose with 1,4-glycosidic bonding and 1,6-branching, more so than amylopectin
24
Q
What is cellulose?
A
Long, unbranched chains of beta glucose with beta 1,4-glycoside linkages.
25
What is the method for Benedict's test for reducing sugars?
Add 2cm3 of the sample solution and 2cm3 Benedict's reagent to a test tube, then heat the mixture for 1 minute. If reducing sugars are present there will be a colour change from blue to brick red
26
What is Benedict's reagent?
A mixture of sodium citrate, copper(II) sulphate and sodium carbonate.
27
What are reducing sugars and non-reducing sugars?
Non-reducing sugars do not have an aldehyde group so they can't reduce copper(I) (blue) to copper(II) red
28
What is the test for non-reducing sugars?
First, carry out the Benedict's test. Then add dilute HCl to a fresh sample and boil the mixture. This hydrolyses the sugar into constituent monosaccharides. Add sodium hydrogen carbonate to neutralise the acid and then repeat the Benedict's test and there should be a colour change from blue to brick red
29
What is the iodine test for starch?
Add potassium iodide to the test solution. If the solution turns a blue-black colour, starch is present.
30
Name 2 groups of lipids
Triglycerides and phospholipids
31
How are triglycerides formed?
One molecule of glycerol is joined with three fatty acid chains via a condensation reaction, forming 3 ester bonds
32
What are phospholipids made of?
A molecule of glycerol, 2 fatty acids and a phosphate group
33
What is the emulsion test for lipids?
Crush the food sample, then add 2cm3 of ethanol to the sample in a test tube and shake the tube. Decant the mixture into a new test tube and add 2cm3 water. If a layer of cloudy white suspension forms, lipid is present.
34
What are the monomers of proteins?
Amino acids
35
Whats the general structure of an amino acid
R NH2 represents an amine
| COOH is carboxyl group
H2N-----C------COOH
| R represents a variable
H
36
What is the bond between amino acids?
In a condensation reaction between 2 amino acids, a peptide bond forms
37
Primary protein structure
The sequence and number of amino acids in the polypeptide chain.
38
Secondary protein structure
The way the polypeptide chain folds due to hydrogen bonds between amino acids, which gives the polypeptides either an alpha-helix or beta-pleated-sheet shape.
39
Tertiary protein structure
The final 3D structure of a polypeptide chain based on the disulphide bridges and ionic bonding, as well as hydrogen bonds and hydrophobic and hydrophilic interactions.
40
Quaternary structure
When a protein is made of multiple polypeptide chains, the quaternary structure is the arrangement of these chains.
41
Which structure breaks down when a protein is denatured?
The tertiary structure is changed because some of the bonds are broken
42
What are the two types of 3D structure of proteins?
Globular or fibrous
43
What is a globular protein?
These form ball-like structures where hydrophobic parts of the chain face inwards. The hydrophilic parts facing outwards makes globular proteins water soluble, so they're suitable as metabolites.
44
What is a fibrous protein ?
A protein with a long fibre, mostly consisting of repeated amino acid sequences, which are insoluble in water. These usually have structural roles.
45
What are disulphide bonds?
Where, between two cysteine amino acids, a strong double bond is formed between the sulphur atoms.
46
What is haemoglobin?
A globular and therefore water soluble protein consisting of 2 alpha polypeptide chains and 2 beta polypeptide chains, as well as an inorganic prosthetic haem group, which contains an Fe2+ ion.
47
What is the function of haemoglobin?
Haemoglobin carries oxygen around the body through the blood . The oxygen molecules can bind to the iron in the haem group. There are 4 haem groups per haemoglobin, and so each haemoglobin can bind 4 oxygens at any one time.
48
What is collagen?
A fibrous protein consisting of 3 alpha polypeptides wound around each other, with hydrogen bonds between the chains. Collagen molecules can form covalent cross links with other collagen molecules.
49
What is the function of collagen?
Collagen is a structural protein, forming the structure of bones, making up cartilage and connective tissue. Collagen is the main component of tendons that connect skeletal muscle to bones.
50
What is the buret test for proteins?
Crush the solid food and mix it with deionised water to form a liquid sample if necessary. Then add 2cm3 of this sample to a test tube. Add 2cm3 of sodium hydroxide and mix carefully. Then add a few drops of 1% copper(II) sulphate and if peptide bonds are present, the solution will turn from blue to a purple colour.
51
How does an enzyme work?
An enzyme provides an alternative pathway for a reaction to take, which requires a lower activation energy. This speeds up the rate of reaction because more particles have the energy required to react
52
Describe the induced fit model
Substrates must be complementary in shape to the active sites of enzymes. They do not have to be exactly the right shape, as structural changes can occur in the active site, induced by the substrate, to make the active site fit the substrate more precisely. After the reaction the active site returns to its original shape.
53
Why determines the properties of enzymes?
Their active site shape determines the reactions they can catalyse, which is dependent on the tertiary structure of the enzyme.
54
What factors affect rate of enzyme-controlled reactions?
Substrate concentration, enzyme concentration, inhibitor concentration, pH and temperature.
55
What is a competitive inhibitor?
Competitive inhibitors have a similar shape to the substrate and therefore are complementary to the active site of the enzyme. These inhibitors compete with substrates to bind to active sites, and once bound, they block the active sites so enzyme-substrate complexes cannot form. This decreases the rate of reaction.
56
What are non-competitive inhibitors?
These inhibitors do not have to be similar in shape to the substrates as they do not bind to active sites. Instead, they bind to enzymes surface away from the active site. This changes the tertiary structure of the enzymes and therefore the shape of the active sites, making substrates no longer complementary. This means enzyme-substrate complexes cannot form and rate of reaction is decreased.
57
What came before the induced fit model for enzyme function?
The lock and key model, which suggested that the substrate had to be exactly complementary to the active sites of the enzymes with which they'd form complexes.
58
What is DNA?
Deoxyribonucleic acid, a polymer of nucleotides. DNA is the molecule from which alleles on chromosomes are made.
59
What is the structure of DNA?
DNA is made of two nucleotide chains that coil around each other in a double helix in which the two polynucleotides run antiparallel to each other, with hydrogen bonds between adjacent nucleotides (A and T, C and G)
60
What are nucleotides?
Nucleotides are the monomers of nucleic acids such as DNA and RNA. They are made of a pentose sugar such as deoxyribose, joined to a phosphate group and a nitrogenous base.
61
How do nucleotides join together?
Nucleotides join together by the sugar of one nucleotide to the phosphate group of the next, which is called the backbone of the molecule. The 3' carbon of one sugar is joined to the 5' carbon of the next by a phosphate bridge. The sugar-phosphate-sugar bonds are called phosphodiester bonds.
62
What are the 4 nitrogenous bases ?
A- Adenine
T- Thymine
C- Cytosine
G- Guanine
63
What is RNA?
RNA is the same as DNA, but instead of having a deoxyribose sugar, RNA nucleotides have a ribose sugar.
64
How is RNA different to DNA?
| 4 ways
RNA has a different pentose sugar.
RNA is a single stranded molecule.
RNA is a much smaller molecule than DNA.
There is never pyrimidine Thymine, but instead pyrimidine Uracil.
65
What are the 3 different forms of RNA?
Ribosomal RNA
Messenger RNA
Transfer RNA
66
What is ribosomal RNA?
Ribosomal RNA is involved in the formation of ribosomes and is therefore important to protein synthesis. Ribosomal RNA makes up 80% of the RNA in a cell.
67
What is messenger RNA?
Messenger RNA forms the nucleus and is used to communicate the genetic code in the allele to the ribosome during protein synthesis. mRNA makes up 3-5% of the RNA in a cell.
68
What is Transfer RNA?
Transfer RNA is clover leaf shaped molecule involved in carrying amino acids through the cytoplasm to their correct places in a growing polypeptide chain during translation. tRNA makes up up to 15% of the RNA in a cell.
69
What is genetic code?
The genetic code is a set of rules by which information encoded in genetic material is translated into proteins by living cells.
The genetic code consists of 64 base triplets of nucleotides. Each codon codes for one of the 20 possible amino acids.
70
Why can the genetic code be described as degenerate?
The same amino acid is coded for by more than one codon.
71
Why can the genetic code be described as non-overlapping?
Adjacent codons do not overlap. The same letter (base) is never used for 2 codons.
(ACGTAC is two codons: ACG and TAC, not CGT or GTA)
72
Why can the genetic code be described as comma less?
There is no signal of where one codon ends and the next one starts, always they are always separate and non-overlapping.
73
Why can the genetic code be described as non-ambiguous?
A specific codon always codes for the same amino acid and never codes for more than one.
74
Why can the genetic code be described as universal?
Codons code for the same amino acids in all organisms
75
Why can the genetic code be described as having polarity?
The genetic code must always be read in a particular direction, the 5' to 3' direction.
76
What is a purine base?
Adenine and guanine are purine bases with a double ring structure.
77
What is a pyrimidine base?
Cytosine, thymine and uracil are pyrimidine as they have a single ring structure.
78
What is the function of DNA?
DNA contains the instructions for making proteins.
79
What is complementary base pairing?
Where adenine hydrogen bonds to thymine and cytosine hydrogen bonds to guanine in the double helix of DNA, which creates consistency
80
What are chromosomes?
Chromosomes are made of two DNA double helices with hydrogen bonds between the complementary base pairs.
81
What is a gene?
A section of DNA that codes for the synthesis of a single polypeptide.
82
What is semi-conservative replication of DNA?
The parent DNA molecule splits into its two separate strands, each of which acts as a template for the formation of new complementary strands. The two daughter DNA molecules therefore have half the parent DNA and half the new DNA.
83
How was semi-conservative replication proven by Meselsohn and Stahl in 1958?
They grew the bacterium E. coli in the presence of radioactive 15N until a culture was formed with all the DNA labelled with 15N.
A subculture of this was then transferred to grow in the presence of normal 14N. The generation time of E. coli was known, so they could take samples of the subculture after each generation. Each sample had its DNA extracted and the isolated DNA was centrifuged in caesium chloride solution. The heavier the DNA, the further it moved down the centrifuge tube, so 15N was lower than 14N. Mixed 14N ad 15N gave an intermediate weight and height.
After 1 generation, al the DNA was at intermediate height, indicating a mixture of 14N and 15N. This shows that the DNA was made of a parent strand and a new daughter strand, indicating semi-conservative replication. The conservative model would have given 1 heavy band ad 1 light band.
84
What is the first step of DNA replication?
One strand of the DNA duplex is nicked by DNA topoisomerase , allowing part of the molecule to unravel to form a replication fork.
85
What is the second step of DNA replication?
DNA helicase enzyme splits the two strands of DNA by breaking the hydrogen bonds, which exposes the bases. DNA helicase enzymes use energy from ATP hydrolysis to separate the parental strands. Each parental strand will then act as a template for synthesis of a daughter strand.
86
What is the third step of DNA replication?
DNA polymerase enzyme moves along the exposed bases, creating a new complementary strand as it goes. DNA polymerase reads the exposed base sequence in the 3' to 5' direction, then assembles the new strand from 5' to 3'. Several DNA polymerase enzymes work simultaneously, each assembling separate sections of the new DNA strand.
87
What is the role of the RNA polymerase which precedes DNA polymerase?
Each DNA polymerase is preceded by an RNA polymerase enzyme, which constructs an RNA primer to guide the action of the DNA polymerase. The primer marks the starting point for the synthesis of the new strand.
88
What is the fifth step of DNA replication?
The new DNA segments are then joined together by the enzyme DNA ligase. The two new daughter strands of DNA then coil up into double helices, a process which occurs in the S phase of the cel cycle.
89
What is ATP?
Adenosine triphosphate is a nucleotide derivative formed from a molecule of ribose, a molecule of adenine and three phosphate groups.
90
Where is the energy in ATP stored?
Energy is held in the form of the phosphate bonds.
91
How is energy released from ATP?
ATP is hydrolysed by ATP hydrolase enzymes into ADP (adenine diphosphate) and an inorganic phosphate. The inorganic phosphate can be used to phosphorylate other compounds
92
How is ATP resynthesised?
ATP synthase catalyses the condensation of ADP and Pi during photosynthesis or respiration.
93
What are the 6 important properties of water?
* Water is a metabolite in many reactions, including condensation and hydrolysis reactions
* Water is an excellent solvent for ions and polar molecules due to its own polarity, so water can form hydrogen bonds with polar molecules.
* Water has a relatively large latent heat of vaporisation , providing a cooling effect with little loss of water through evaporation, explaining sweating and panting.
* Water has a high heat capacity, buffering changes in temperature. This makes thermostasis easier.
* Water has strong cohesion between water molecules; this allows water to move through plants in long unbroken columns in xylem tissue, and produces surface tension where water meets air
