Biological molecules Flashcards
Topic 1
1
Q
Why is the biochemical basis of life similar for all organisms?
A
Despite extensive diversity, all living organisms share key biological molecules (DNA, RNA, proteins, carbohydrates, and lipids).
2
Q
What are monomers?
A
Monomers are small molecules that join to form polymers. Examples: monosaccharides, amino acids, and nucleotides.
3
Q
What are polymers?
A
Polymers are large molecules made of repeating monomers. Examples: polysaccharides, proteins, and nucleic acids.
4
Q
What is a condensation reaction?
A
A reaction that joins molecules by forming a chemical bond while removing water (H₂O).
5
Q
What is a hydrolysis reaction?
A
A reaction that breaks a chemical bond by adding water (H₂O), splitting polymers into monomers.
6
Q
What are monosaccharides? Give examples.
A
Monosaccharides are carbohydrate monomers. Examples: glucose, galactose, and fructose.
7
Q
What bond forms between two monosaccharides?
A
A glyosidic bond forms through a condensation reaction.
8
Q
How are disaccharides formed? Give examples.
A
Disaccharides form via condensation of two monosaccharides:
Maltose = glucose + glucose
Sucrose = glucose + fructose
Lactose = glucose + galactose
9
Q
What are the two isomers of glucose?
A
α-glucose and β-glucose, differing in the position of the hydroxyl (-OH) group on carbon 1
10
Q
How are polysaccharides formed?
A
By condensation of many glucose monomers.
11
Q
Which polysaccharides are formed from α-glucose and β-glucose?
A
Glycogen & Starch → α-glucose
Cellulose → β-glucose
12
Q
How do you test for reducing sugars?
A
Benedict’s test:
Add Benedict’s reagent (blue) to the sample.
Heat in a water bath at 90°C for 5 minutes.
Positive result: Color change from blue → green → yellow → orange → brick red (depending on sugar concentration).
Negative result: Solution remains blue.
13
Q
How do you test for non-reducing sugars?
A
Benedict’s test (after hydrolysis):
If the initial Benedict’s test is negative (solution stays blue), hydrolyze the sugar by adding dilute hydrochloric acid and heating.
Neutralize with sodium hydrogen carbonate.
Re-test with Benedict’s reagent and heat.
Positive result: Brick red precipitate forms.
Negative result: Solution remains blue.
14
Q
How do you test for starch?
A
Iodine test:
Add potassium iodide solution to the sample.
Positive result: Color change from orange-brown → blue-black (starch present).
Negative result: Solution stays orange-brown.
15
Q
What is the structure and function of starch?
A
Structure: Made of α-glucose monomers, linked by glycosidic bonds.
Composed of:
Amylose – Long, unbranched, coiled structure (compact for storage).
Amylopectin – Branched, allowing enzymes to quickly break down glucose.
Function: Energy storage in plants (insoluble, does not affect water potential).
16
Q
What is the structure and function of glycogen?
A
Structure: Made of α-glucose, highly branched (more than amylopectin).
Function:
Energy storage in animals (liver & muscles).
Many branches allow rapid hydrolysis for quick energy release.
Insoluble, so it does not affect water potential.
17
Q
What is the structure and function of cellulose?
A
Structure: Made of β-glucose monomers, forming long, straight chains.
Chains are linked by hydrogen bonds, forming microfibrils (strong fibers).
Function: Provides structural support in plant cell walls, making them rigid.
18
Q
What are the two main types of lipids?
A
Triglycerides and Phospholipids.
19
Q
How are triglycerides formed?
A
One glycerol molecule + three fatty acids.
Joined by condensation reactions, forming ester bonds.
Insoluble in water (hydrophobic).
20
Q
What is an ester bond?
A
A covalent bond formed in a condensation reaction between glycerol and fatty acids, with the removal of water (H₂O).
21
Q
What is the difference between saturated and unsaturated fatty acids?
A
Saturated – No C=C double bonds, straight chains, solid at room temp (e.g., animal fats).
Unsaturated – One or more C=C double bonds, kinks in chain, liquid at room temp (e.g., oils).
22
Q
How do phospholipids differ from triglycerides?
A
In phospholipids, one fatty acid in a triglyceride is replaced by a phosphate group.
23
Q
How does structure relate to function in triglycerides and phospholipids?
A
Triglycerides – Energy storage, hydrophobic, insoluble, compact.
Phospholipids – Form bilayers in cell membranes, have hydrophilic heads & hydrophobic tails (amphipathic).
24
Q
What is the emulsion test for lipids?
A
Mix sample with ethanol and shake.
Add water and shake again.
Positive result: Milky-white emulsion (lipids present).
25
How to recognize saturated vs. unsaturated fatty acids in diagrams?
Saturated – No C=C double bonds, straight-chain.
Unsaturated – At least one C=C double bond, kinked-chain.
26
What are the main roles of lipids in organisms?
Energy storage – Triglycerides provide twice the energy per gram compared to carbohydrates.
Waterproofing – Waxy cuticles in plants & oil secretion in animals prevent water loss.
Insulation – Lipids act as heat insulators (e.g., in adipose tissue) and electrical insulators (e.g., myelin sheath around neurons).
Protection – Fat cushions organs, reducing physical damage.
27
How do phospholipids contribute to membrane structure?
Form phospholipid bilayers in cell membranes.
Hydrophilic heads face water, hydrophobic tails face inward.
Allow selective permeability, controlling substance movement.
28
How do lipids provide metabolic water?
Lipids release metabolic water when oxidized, crucial for desert animals (e.g., camels store fat in humps).
29
What are amino acids?
Monomers that make up proteins. Each amino acid has:
Amine group (-NH₂)
Carboxyl group (-COOH)
R group (side chain, varies for each amino acid)
30
How do amino acids form peptides?
Condensation reaction between two amino acids forms a peptide bond.
Dipeptide = 2 amino acids.
Polypeptide = Many amino acids.
31
What are the four levels of protein structure?
Primary – Sequence of amino acids in a polypeptide.
Secondary – Hydrogen bonds form α-helices or β-pleated sheets.
Tertiary – Further folding due to hydrogen bonds, ionic bonds, and disulfide bridges.
Quaternary – Multiple polypeptides combine (e.g., hemoglobin).
32
What bonds are involved in protein structure?
Hydrogen bonds – Weak, but provide stability.
Ionic bonds – Form between charged R groups.
Disulfide bridges – Strong covalent bonds between sulfur atoms in cysteine.
33
What are the functions of proteins?
Enzymes – Speed up reactions (e.g., amylase).
Transport – Hemoglobin carries oxygen.
Structural – Collagen strengthens tissues.
Hormones – Insulin regulates blood sugar.
Antibodies – Defend against pathogens.
34
What is the Biuret test for proteins?
Add Biuret reagent (sodium hydroxide + copper sulfate).
Positive result: Purple/lilac color (protein present).
Negative result: Solution remains blue.
35
How does protein structure relate to function?
Globular proteins (e.g., enzymes) → Compact, soluble, functional roles.
Fibrous proteins (e.g., collagen) → Long, strong, structural roles.
36
What is the primary structure of a protein?
The sequence of amino acids in a polypeptide chain.
Determined by DNA and held together by peptide bonds.
Even a single amino acid change can affect protein function (e.g., sickle cell anemia).
37
What is the secondary structure of a protein?
Folding of the polypeptide chain due to hydrogen bonding.
Forms two main structures:
α-helix → Coiled, stabilized by H-bonds (e.g., keratin).
β-pleated sheet → Folded, held by H-bonds (e.g., silk).
38
What is the tertiary structure of a protein?
Further folding of the polypeptide into a 3D shape.
Stabilized by different bonds:
Hydrogen bonds – Weak but numerous, provide stability.
Ionic bonds – Between charged R groups, stronger than H-bonds.
Disulfide bridges – Strong covalent bonds between cysteine residues.
Determines protein function (e.g., enzyme active site shape).
39
What is the quaternary structure of a protein?
When two or more polypeptides associate to form a functional protein.
Example proteins:
Hemoglobin – 4 polypeptide chains, carries oxygen.
Collagen – 3 polypeptide chains, provides structural support.
40
What is the role of enzymes in biochemical reactions?
Enzymes lower the activation energy of reactions, making them occur more easily and quickly.
This speeds up the rate of the reaction without being consumed in the process.
41
What is the induced-fit model of enzyme action?
The active site of the enzyme is flexible and changes shape when the substrate binds.
The binding of the substrate induces the enzyme to adopt a complementary shape, leading to a better fit and facilitating the reaction.
This contrasts with the lock-and-key model, where the active site is a rigid, fixed structure.
42
How does the tertiary structure of an enzyme relate to its function?
The tertiary structure determines the precise shape of the enzyme’s active site, which is essential for the enzyme to recognize and bind to its specific substrate(s).
Only substrates with a complementary shape can bind to the active site and form an enzyme-substrate complex.
43
What is enzyme specificity?
Enzymes are specific to their substrates due to the shape of their active site.
Each enzyme catalyzes only one type of reaction or a small group of related reactions, based on the fit between the enzyme’s active site and its substrate.
44
How does enzyme concentration affect the rate of enzyme-controlled reactions?
Increasing enzyme concentration increases the rate of reaction, provided there is sufficient substrate.
More enzyme molecules mean more active sites available for substrate binding.
45
How does substrate concentration affect the rate of enzyme-controlled reactions?
Increasing substrate concentration increases the rate of reaction, but only up to a certain point.
At high substrate concentrations, the active sites of enzymes become saturated, and the rate levels off because all enzyme molecules are occupied.
46
What is the effect of competitive inhibitors on enzyme activity?
Competitive inhibitors resemble the substrate and compete for the same active site on the enzyme.
Higher substrate concentration can overcome the effects of competitive inhibition by outcompeting the inhibitor for the active site.
The rate of reaction decreases in the presence of competitive inhibitors.
47
What is the effect of non-competitive inhibitors on enzyme activity?
Non-competitive inhibitors bind to a site other than the active site, called an allosteric site, causing a change in the enzyme's shape.
This reduces the enzyme’s activity and prevents the enzyme from forming an effective enzyme-substrate complex.
Increasing substrate concentration does not overcome non-competitive inhibition.
48
How does pH affect enzyme activity?
Each enzyme has an optimal pH at which it works most efficiently.
Deviation from the optimal pH can cause the enzyme to lose its tertiary structure, reducing its ability to bind with the substrate.
Extreme pH values can denature enzymes, permanently altering their shape.
49
How does temperature affect enzyme activity?
Increasing temperature generally increases enzyme activity because molecules move faster, leading to more frequent collisions between enzymes and substrates.
However, at temperatures above the optimum temperature, enzymes can denature, losing their shape and, therefore, their function.
50
How have models of enzyme action changed over time?
The lock-and-key model (first proposed) suggested that the enzyme's active site was a rigid, specific shape that matched the substrate like a key in a lock.
The induced-fit model (more recent) proposes that the enzyme's active site is more flexible and adapts to fit the substrate upon binding. This model is now accepted because it accounts for the dynamic nature of enzymes.
51
Why are enzymes important for life at both cellular and organism levels?
Enzymes catalyze a wide range of reactions that control cellular processes, such as metabolism, DNA replication, and protein synthesis.
They also play a crucial role in extracellular reactions like digestion and nutrient absorption, influencing the function and structure of cells and tissues throughout the organism.
Without enzymes, many biochemical reactions would occur too slowly to sustain life.
52
What are the main functions of DNA and RNA?
DNA (Deoxyribonucleic acid) holds genetic information in cells.
RNA (Ribonucleic acid) transfers genetic information from DNA to the ribosomes for protein synthesis.
53
What are ribosomes made from?
Ribosomes are made of RNA and proteins.
RNA in the ribosome plays a role in protein synthesis.
54
What are DNA and RNA composed of?
Both DNA and RNA are polymers made up of nucleotides.
A nucleotide consists of:
Pentose sugar (ribose in RNA, deoxyribose in DNA)
Nitrogenous base (Adenine, Cytosine, Guanine, Thymine in DNA; Uracil replaces Thymine in RNA)
Phosphate group
55
What are the components of a DNA nucleotide?
Deoxyribose (pentose sugar)
Phosphate group
One of the following nitrogenous bases:
Adenine (A)
Cytosine (C)
Guanine (G)
Thymine (T)
56
What are the components of an RNA nucleotide?
Ribose (pentose sugar)
Phosphate group
One of the following nitrogenous bases:
Adenine (A)
Cytosine (C)
Guanine (G)
Uracil (U) (instead of Thymine in DNA)
57
How is a phosphodiester bond formed between nucleotides?
A condensation reaction between the phosphate group of one nucleotide and the pentose sugar of another nucleotide forms a phosphodiester bond.
This bond links the nucleotides into a polynucleotide chain.
58
Describe the structure of a DNA molecule.
DNA is a double helix structure, consisting of two polynucleotide chains.
The two strands are held together by hydrogen bonds between complementary nitrogenous base pairs:
Adenine (A) pairs with Thymine (T)
Cytosine (C) pairs with Guanine (G)
59
Describe the structure of an RNA molecule.
RNA is a single-stranded polynucleotide chain.
RNA is typically shorter than DNA and contains Uracil (U) instead of Thymine.
60
Why did many scientists initially doubt that DNA carried genetic information?
The relative simplicity of DNA, being made up of only four bases, led many scientists to doubt that it could store such complex genetic information.
Scientists initially thought that proteins, with their greater variety of amino acids, were more likely candidates for carrying genetic information.
61
Why is DNA stable?
DNA is stable due to its double-helix structure and the presence of hydrogen bonds between complementary base pairs.
The phosphodiester backbone of the polynucleotide strands is strong and protects the genetic material inside.
62
How do hydrogen bonds contribute to the stability of DNA?
Hydrogen bonds between complementary base pairs (A-T and C-G) help to hold the two strands together.
Although individual hydrogen bonds are weak, there are many of them, which collectively provide significant stability to the DNA structure.
The more C-G pairs in DNA, the more stable the molecule, as they form three hydrogen bonds, compared to the two formed by A-T pairs.
63
How does the double-helix structure of DNA contribute to its stability?
The double-helix structure of DNA allows for the bases to be stacked inside, away from external chemical attacks, which makes the molecule more stable.
The two strands of DNA are antiparallel and are held together in a twisted shape, which makes the molecule less likely to undergo damage.
64
What is the primary function of DNA in living organisms?
The primary function of DNA is to store and transmit genetic information that is essential for growth, development, and functioning of an organism.
DNA carries the instructions for protein synthesis and cellular activities through its genetic code.
65
How does DNA store genetic information?
DNA stores genetic information in the form of sequences of nitrogenous bases (A, T, C, G) along its double-stranded structure.
The sequence of these bases encodes the instructions for the synthesis of proteins, which carry out the functions within the cell.
66
What is the main principle of semi-conservative replication of DNA?
In semi-conservative replication, each new DNA molecule consists of one original strand (template strand) and one newly synthesized strand.
This ensures genetic continuity between generations of cells, with each daughter cell receiving an identical copy of the DNA.
67
What happens during the unwinding of the DNA double helix in semi-conservative replication?
The double helix of DNA unwinds to separate the two strands, making them available as templates for the formation of new complementary strands.
This unwinding is the first step in DNA replication.
68
What is the role of DNA helicase in semi-conservative replication?
DNA helicase is an enzyme that unwinds the DNA double helix by breaking the hydrogen bonds between the complementary base pairs, separating the two polynucleotide strands.
69
How does DNA helicase break the hydrogen bonds between complementary bases in the polynucleotide strands?
DNA helicase breaks the hydrogen bonds between complementary bases (A-T, C-G), causing the two strands to separate.
This exposes the bases of the original strand, allowing new nucleotides to bind according to the base-pairing rule.
70
How are new DNA nucleotides attracted to the exposed bases on the template strands?
The exposed bases on the template strand attract complementary free nucleotides (A with T, C with G).
These nucleotides are aligned by base pairing, ensuring that the new strand is complementary to the original strand
71
What is the role of DNA polymerase in semi-conservative replication?
DNA polymerase is an enzyme that catalyzes the condensation reaction between adjacent nucleotides, forming the phosphodiester bonds that join the nucleotides together, creating the new strand of DNA.
It also proofreads the newly formed strand to ensure accuracy in base pairing.
72
How does base pairing occur during DNA replication?
During semi-conservative replication, the exposed bases on the template strand attract complementary free nucleotides from the surrounding pool of nucleotides.
Adenine (A) pairs with Thymine (T), and Cytosine (C) pairs with Guanine (G), ensuring accurate replication.
73
What happens after the condensation reactions in DNA replication?
After DNA polymerase catalyzes the condensation reaction, the new nucleotides are joined to the growing polynucleotide strand.
This forms a new DNA strand, which is complementary to the template strand.
74
What evidence supports the semi-conservative model of DNA replication?
The Meselson-Stahl experiment (1958) provided strong evidence for the semi-conservative model.
They grew bacteria in a medium containing heavy nitrogen (N-15) and then transferred them to a medium with lighter nitrogen (N-14).
After one round of replication, the DNA had an intermediate density, indicating that each DNA molecule consisted of one old strand and one new strand, confirming semi-conservative replication.
75
How does the Watson-Crick model explain DNA replication?
The Watson-Crick model of DNA replication proposed that the double helix unwinds and separates into two strands.
Each strand serves as a template for the formation of a new complementary strand through base pairing.
This model was confirmed by experimental evidence, particularly the results of the Meselson-Stahl experiment, validating the semi-conservative nature of DNA replication.
76
What is the difference between nuclear division and cytokinesis in cell division?
Nuclear division refers to the division of the nucleus during mitosis or meiosis, which includes the separation of chromosomes into two daughter nuclei.
Cytokinesis is the process that follows nuclear division, where the cytoplasm is divided, resulting in the formation of two distinct daughter cells.
In animal cells, cytokinesis involves the formation of a cleavage furrow.
In plant cells, a cell plate forms to separate the daughter cells.
77
What is the structure of a molecule of ATP?
ATP (Adenosine triphosphate) is a nucleotide derivative composed of:
A ribose sugar
The nitrogenous base adenine
Three phosphate groups (linked by high-energy bonds)
78
What is the process of ATP hydrolysis?
The hydrolysis of ATP involves breaking the bond between the second and third phosphate groups, producing ADP (Adenosine diphosphate) and an inorganic phosphate (Pi).
This reaction is catalyzed by the enzyme ATP hydrolase.
79
What is the role of ATP hydrolysis in energy transfer?
The hydrolysis of ATP to ADP and Pi releases energy that can be coupled to energy-requiring reactions in the cell.
This process drives various cellular activities like muscle contraction, active transport, and protein synthesis.
80
How does the inorganic phosphate (Pi) released during ATP hydrolysis affect other molecules?
The Pi released can be used to phosphorylate other molecules, often making them more reactive and enabling them to participate in biochemical reactions.
Phosphorylation can change the shape or activity of a molecule, such as enzymes or substrates.
81
How is ATP resynthesized in cells?
ATP is resynthesized from ADP and inorganic phosphate (Pi) in a process known as phosphorylation.
This process is catalyzed by the enzyme ATP synthase during photosynthesis (in plants) or cellular respiration (in mitochondria).
82
What is the role of water as a metabolite in metabolic reactions?
Water acts as a metabolite in many biochemical reactions, including condensation (joining molecules by removing water) and hydrolysis (breaking bonds by adding water).
These reactions are essential for building and breaking down complex molecules in cells.
83
How does water function as an important solvent in biological systems?
Water is a polar solvent, meaning it can dissolve a wide variety of substances, particularly ionic compounds and polar molecules.
This property makes it an ideal medium for metabolic reactions, allowing ions, gases, and molecules to move and interact in cells.
84
How does water's high heat capacity benefit living organisms?
Water has a high heat capacity, meaning it can absorb and retain a lot of heat without a significant change in temperature.
This helps buffer organisms and ecosystems from rapid temperature fluctuations, maintaining thermal stability and supporting enzyme activity.
85
What is the significance of water's latent heat of vaporisation?
Water has a high latent heat of vaporisation, meaning it requires a large amount of heat to convert from liquid to gas.
This provides a cooling effect when water evaporates, helping organisms regulate temperature with minimal loss of water, which is crucial for maintaining homeostasis.
86
How does water's cohesion benefit plant transport systems?
Water molecules have strong cohesion, meaning they stick together due to hydrogen bonding.
This property supports the movement of water columns in the tube-like transport cells (xylem) of plants, enabling water to travel from roots to leaves.
87
How does water's cohesion and surface tension affect its behavior at air interfaces?
Water's cohesion creates surface tension at the interface between water and air, allowing water to form droplets and supporting small organisms that move on the surface of water.
This surface tension also aids in the formation of meniscus in plant capillaries, assisting in capillary action.
88
What role do hydrogen ions (H⁺) play in biology?
Hydrogen ions (H⁺) determine the pH of a solution.
A high concentration of H⁺ results in an acidic environment, while a low concentration results in an alkaline environment.
pH affects enzyme activity, protein structure, and cell function.
89
How are iron ions (Fe²⁺) important in the body?
Iron ions (Fe²⁺) are a key component of hemoglobin, which is found in red blood cells.
They bind to oxygen in the lungs and transport it through the bloodstream to tissues throughout the body.
Iron is essential for oxygen transport and overall respiratory function.
90
What is the role of sodium ions (Na⁺) in the co-transport of glucose and amino acids?
Sodium ions (Na⁺) are involved in the co-transport mechanism, particularly in the intestinal epithelium.
Na⁺ ions are actively transported out of cells via the sodium-potassium pump, creating a concentration gradient.
Glucose or amino acids are co-transported into cells alongside Na⁺ ions, using the energy stored in the sodium gradient to facilitate their absorption.
91
What role do phosphate ions (PO₄³⁻) play in biological molecules?
Phosphate ions (PO₄³⁻) are components of important biological molecules, such as DNA and ATP.
In DNA, phosphate groups form part of the backbone of the DNA molecule.
In ATP, phosphate groups are part of the molecule's high-energy bonds that store and release energy during cellular processes.
