Water:The Molecule of Life
Which statement best helps explain the formation of hydrogen bonds between water and other polar molecules like ammonia?
a) The oxygen atom always has a partial positive charge.
b) A hydrogen atom attached to an oxygen atom has a partial positive charge and can be attracted to a partial negative charge on another electronegative atom.
c) Hydrogen atoms always have a partial negative charge.
d) All atoms in a molecule share electrons equally in a covalent bond.
b) A hydrogen atom attached to an oxygen atom has a partial positive charge and can be attracted to a partial negative charge on another electronegative atom.
Which of the following elements is a key component of all biological macromolecules?
a) Calcium
b) Iron
c) Carbon
d) Potassium
c) Carbon
Which of the following is a primary function of carbohydrates in living organisms?
a) Storing genetic information
b) Catalysing biological reactions
c) Providing a source of energy
d) Forming the main structure of cell membranes
c) Providing a source of energy
Proteins are polymers made up of which of the following monomers?
a) Nucleotides
b) Monosaccharides
c) Amino acids
d) Fatty acids
c) Amino acids
The property of water that allows insects to walk on its surface is primarily due to:
a) Water's polarity
b) Surface tension
c) Water's high specific heat
d) Adhesion
b) Surface tension
Due to water's polarity and ability to form hydrogen bonds, which of the following properties allows a water column to move up a plant stem from the roots to the leaves?
a) High specific heat
b) Cohesion and adhesion
c) Universal solvent properties
d) Neutral pH
b) Cohesion and adhesion
The process by which monomers are linked together to form polymers with the removal of a water molecule is called:
a) Hydrolysis
b) Dehydration synthesis
c) Oxidation
d) Reduction
b) Dehydration synthesis
The bond formed between two monosaccharides during a dehydration reaction is called a:
a) Peptide bond
b) Ester linkage
c) Glycosidic linkage
d) Phosphodiester bond
c) Glycosidic linkage
The genetic information of a cell is primarily stored in which type of nucleic acid?
a) Messenger RNA (mRNA)
b) Transfer RNA (tRNA)
c) Ribosomal RNA (rRNA)
d) Deoxyribonucleic acid (DNA)
d) Deoxyribonucleic acid (DNA)
Which of the following best describes the process of dehydration synthesis?
a) The breakdown of a polymer into monomers by the addition of water.
b) The formation of hydrogen bonds between water molecules and monomers.
c) The linking of monomers to form a polymer with the removal of a water molecule.
d) The dissolving of a solute in a solvent like water.
c) The linking of monomers to form a polymer with the removal of a water molecule.
Surface tension in water is a direct result of which of the following?
a) The large size of water molecules
b) Water's ability to dissolve many substances
c) The cohesive forces between water molecules due to hydrogen bonding at the surface
d) The low density of ice compared to liquid water
c) The cohesive forces between water molecules due to hydrogen bonding at the surface
Glucose, galactose, and fructose are monosaccharides with the same chemical formula (C6H12O6) but different:
a) Numbers of carbon atoms
b) Types of chemical bonds
c) Structural formulas
d) Molecular weights
c) Structural formulas
Which of the following best describes the key difference between saturated and unsaturated fatty acids?
a) Unsaturated fatty acids contain more carbon atoms than saturated fatty acids.
b) Unsaturated fatty acids contain carbon-to-carbon double bonds, while saturated fatty acids do not.
c) Saturated fatty acids are hydrophilic, while unsaturated fatty acids are hydrophobic.
d) Unsaturated fatty acids are solid at room temperature, while saturated fatty acids are liquid.
b) Unsaturated fatty acids contain carbon-to-carbon double bonds, while saturated fatty acids do not.
A peptide bond is formed between which two functional groups of adjacent amino acids?
a) A hydroxyl group and a carboxyl group
b) An amino group and another amino group
c) An amino group and a carboxyl group
d) A phosphate group and a hydroxyl group
c) An amino group and a carboxyl group
The tertiary structure of a protein is primarily determined by:
a) The sequence of amino acids (primary structure).
b) The formation of alpha helices and beta-pleated sheets (secondary structure).
c) The interactions between the R groups of the amino acids.
d) The number of polypeptide subunits (quaternary structure).
c) The interactions between the R groups of the amino acids.
Describe the relationship between water's polarity and its ability to act as a universal solvent for many biological molecules.
Water's polarity, with its partial positive and negative charges, allows it to interact with and dissolve other polar molecules and ionic compounds. The water molecules surround the charged parts of these solutes, disrupting the attractions between the solute molecules or ions and causing them to disperse in the water. This is why water is effective at dissolving many substances important for life
Describe the fundamental difference in structure between a saturated fatty acid and an unsaturated fatty acid, and explain how this difference affects their properties at room temperature.
Saturated fatty acids have no carbon-carbon double bonds in their hydrocarbon chains, resulting in straight chains that can pack closely together, making them solid at room temperature. Unsaturated fatty acids contain one or more carbon-carbon double bonds, creating kinks in the chains that prevent them from packing closely, making them liquid at room temperature
Explain why lipids are classified as hydrophobic macromolecules and describe how this property is essential for the structure and function of cell membranes.
Lipids are considered hydrophobic because they consist primarily of carbon and hydrogen atoms linked by nonpolar covalent bonds. This nonpolar nature means they do not interact favourably with polar water molecules; they are "water-fearing". In cell membranes, this hydrophobic property allows phospholipids to spontaneously form a bilayer with their hydrophobic tails facing inwards, away from the aqueous environment, and their hydrophilic heads facing outwards, interacting with water. This hydrophobic core of the membrane acts as a barrier, controlling the movement of polar molecules and ions into and out of the cell, which is crucial for maintaining cellular function.
Describe the central dogma of molecular biology and explain the roles of both DNA and RNA in this process as they relate to protein synthesis.
The central dogma of molecular biology describes the flow of genetic information within a biological system. It states that DNA is transcribed into RNA, which is then translated into protein. DNA serves as the heritable blueprint containing the genetic code in the sequence of its nucleotide bases. During transcription, the information in a specific segment of DNA (a gene) is copied into a messenger RNA (mRNA) molecule. This mRNA molecule then carries the genetic instructions from the nucleus to the ribosomes in the cytoplasm. At the ribosomes, the process of translation occurs, where the sequence of codons in the mRNA is used to assemble a specific sequence of amino acids, forming a protein. Transfer RNA (tRNA) molecules bring the correct amino acids to the ribosome according to the mRNA codons, and ribosomal RNA (rRNA) is a structural and catalytic component of the ribosome.
Explain how the arrangement of phospholipids in a cell membrane allows for a hydrophobic barrier, and describe how this property is crucial for controlling the passage of different types of molecules into and out of the cell
Phospholipids, which have a hydrophilic (polar) head and two hydrophobic (nonpolar) fatty acid tails, spontaneously arrange themselves in a bilayer in an aqueous environment. The hydrophobic tails face inwards, away from the water, forming a nonpolar interior, while the hydrophilic heads face outwards, interacting with the surrounding water. This hydrophobic core of the membrane acts as a barrier to polar molecules and ions, which cannot easily pass through the nonpolar environment. This selective permeability is crucial for maintaining different concentrations of substances inside and outside the cell, which is essential for various cellular processes like nutrient uptake, waste removal, and maintaining ion gradients for nerve impulse transmission
Explain how the unique arrangement of water molecules and hydrogen bonds in ice (at 0°C) compared to liquid water (at 25°C) contributes to the phenomenon of ice floating, and discuss one consequence of this phenomenon that is biologically significant in aquatic ecosystems
In ice, water molecules form a more ordered, crystalline structure where each water molecule is hydrogen-bonded to four others, creating a relatively open lattice. This arrangement spaces the molecules further apart than in liquid water, making ice less dense. In liquid water, hydrogen bonds are constantly forming and breaking, allowing the molecules to be more closely packed. Because ice is less dense, it floats. A biologically significant consequence of ice floating is that it provides an insulating layer on the surface of lakes and oceans during freezing temperatures. This prevents the entire body of water from freezing solid, allowing aquatic organisms to survive the winter beneath the ice
Explain how the primary structure of a protein determines its tertiary structure, and discuss how a change in the primary structure, such as the deletion of an amino acid (as seen in the CFTR protein example), can impact the protein's overall function and stability.
The primary structure of a protein is the linear sequence of amino acids in its polypeptide chain. This sequence dictates the interactions between the different R groups of the amino acids (hydrophobic, hydrophilic, charged, polar), which then determine how the protein folds into its specific three-dimensional tertiary structure. These interactions include hydrogen bonds, disulfide bonds, ionic bonds, and hydrophobic interactions. A change in the primary structure, such as the deletion of an amino acid, can alter the sequence of R groups and thus disrupt these crucial interactions, leading to a misfolded protein with a different tertiary structure. This altered structure can significantly affect the protein's stability and its ability to bind to its specific ligands or substrates, ultimately impacting its intended function
Compare and contrast the structures and primary functions of polysaccharides like starch in plants and glycogen in animals. Explain how their different structures relate to their roles in energy storage.
Both starch (in plants) and glycogen (in animals) are polysaccharides composed of glucose monomers linked by glycosidic bonds. However, they differ in their structure. Starch exists in two main forms: amylose, which is a linear chain of glucose, and amylopectin, which is branched. Glycogen is also a branched polysaccharide, but it is more extensively branched than amylopectin. This structural difference relates to their roles in energy storage. The branching in both molecules allows for more rapid hydrolysis (breakdown) into glucose when energy is needed because there are more free ends for enzymes to act upon. Glycogen's more extensive branching in animals facilitates a quicker release of glucose to meet the higher and more immediate energy demands of animal cells. Starch in plants serves as a longer-term energy storage and its structure reflects this, with less frequent branching compared to glycogen.
Explain how a single amino acid deletion in the primary structure of a protein, such as the deletion of phenylalanine at position 508 in the CFTR protein, can affect the protein's secondary and tertiary structures, ultimately impacting its function. Additionally, discuss how the presence of disulfide bonds formed by cysteine amino acids can contribute to the stability of a protein's tertiary structure, particularly in organisms living in harsh environments.
The primary structure of a protein, the sequence of amino acids, dictates how the protein folds into its higher levels of structure. The deletion of a single amino acid, like phenylalanine in CFTR, alters the sequence of R groups along the polypeptide chain. This change can disrupt the local interactions that lead to the formation of secondary structures (alpha helices and beta-pleated sheets) because the absence of that specific amino acid affects the way the backbone can twist and fold. Furthermore, the altered sequence of R groups will also change the interactions that determine the overall three-dimensional of the protein, such as hydrophobic interactions, hydrogen bonds, ionic bonds, and van der Waals forces. A misfolded protein often loses its ability to function correctly because its shape is critical for binding to other molecules or catalysing reactions. In the case of CFTR, a misfolded protein due to the phenylalanine deletion leads to cystic fibrosis.
◦Disulfide bonds, formed between the sulfur atoms of two cysteine amino acids (also known as disulfide bridges), are covalent bonds that can form between different parts of a polypeptide chain, contributing significantly to the stability of the tertiary structure. These bonds act as "anchors" that hold different regions of the protein together, making it more resistant to denaturation, especially under stressful conditions. In organisms living in harsh environments, proteins with a greater number of cysteine amino acids and thus more disulfide bonds are likely to be more stable and functional at extreme temperatures or in the presence of disruptive chemicals, increasing the organism's chances of survival.
Compare and contrast the structural features of DNA and RNA, including their sugar components, nitrogenous bases, and typical secondary structure. Explain how these structural differences contribute to their distinct roles in the central dogma of molecular biology
Both DNA and RNA are nucleic acids composed of nucleotides, each containing a phosphate group, a nitrogenous base, and a pentose sugar. However, they have key structural differences. DNA contains deoxyribose as its sugar, while RNA contains ribose, which has an additional hydroxyl group. DNA uses the nitrogenous bases adenine (A), guanine (G), cytosine (C), and thymine (T), whereas RNA uses A, G, C, and uracil (U) in place of thymine. Typically, DNA exists as a double-stranded helix with the two strands running antiparallel and held together by hydrogen bonds between complementary bases (A with T, and C with G). RNA is typically single-stranded and can fold into various three-dimensional shapes. These structural differences relate to their roles. DNA's stable double-stranded structure makes it well-suited for long-term storage of genetic information. RNA's single-stranded nature and ability to fold allow it to play diverse roles in protein synthesis, including carrying genetic information from DNA to ribosomes (mRNA), serving as structural and catalytic components of ribosomes (rRNA), and bringing amino acids to the ribosome (tRNA).