Biology Unit 2: Molecules and Membranes

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Questions and Answers

What type of bond forms between the 5'-phosphate of one nucleotide and the 3'-OH of another nucleotide?

Hydrogen bond

Phosphodiester bond (correct)

Ionic bond

Covalent bond

Which of the following is NOT a function of RNA?

Stores genetic information (correct)

Modulates gene expression

Involved in protein synthesis

Carries information from DNA

Which nitrogenous base is found in RNA but not in DNA?

Thymine

Adenine

Uracil (correct)

Cytosine

In what direction are polynucleotides synthesized?

5' to 3' Signup and view all the answers

What structural feature distinguishes DNA from RNA?

Containing thymine instead of uracil Signup and view all the answers

What is the role of cholesterol-derived hormones like testosterone and estradiol?

Regulate intercellular signaling Signup and view all the answers

Which component contributes to the amphipathic nature of cholesterol?

Hydroxyl group Signup and view all the answers

What is the primary information molecule in cells?

DNA Signup and view all the answers

What is the main function of polysaccharides mentioned?

Markers for cell recognition processes Signup and view all the answers

Which formula represents monosaccharides?

(CH2O)n Signup and view all the answers

Which statement is true about cyclized sugars?

They are predominant forms within cells. Signup and view all the answers

What type of bond joins monosaccharides together?

Glycosidic bond Signup and view all the answers

How does cellulose differ from starch?

Cellulose is a structural component, while starch is for storage. Signup and view all the answers

Which of the following polysaccharides is formed mainly of glucose?

Cellulose Signup and view all the answers

What type of bonds primarily link glucose molecules in glycogen and starch?

a(1 → 4) and a(1 → 6) bonds Signup and view all the answers

What role do carbohydrates play in cell signaling?

They function as markers to direct proteins. Signup and view all the answers

What percentage of the human body weight is made up by oxygen, hydrogen, carbon, and nitrogen?

96.2% Signup and view all the answers

Which of the following is true about water in cells?

It represents 70% or more of cell mass. Signup and view all the answers

What is the primary function of carbohydrates in cells?

Providing energy and serving as starting materials for other compounds. Signup and view all the answers

Which of the following statements about inorganic ions in cells is correct?

They are involved in aspects of cellular metabolism. Signup and view all the answers

Which organic molecule type makes up over 90% of the dry weight of most cells?

Nucleic acids Signup and view all the answers

How do nonpolar molecules behave in an aqueous medium?

They tend to minimize contact with water. Signup and view all the answers

Which of the following ions is categorized as a monovalent cation?

Sodium (Na+) Signup and view all the answers

What role do polysaccharides play in cells?

They store energy and provide structural support. Signup and view all the answers

What is the primary role of phospholipids in cells?

They are the main components of cell membranes. Signup and view all the answers

What characterizes the structure of fatty acids?

They contain a carboxyl group and a hydrocarbon chain. Signup and view all the answers

How are triglycerides formed?

By combining one glycerol molecule with three fatty acids. Signup and view all the answers

Why are triglycerides more efficient energy storage than carbohydrates?

They provide more than twice the energy per weight of degraded material. Signup and view all the answers

What is a key feature of phospholipids that allows them to form membranes?

They are amphipathic with both hydrophobic and hydrophilic parts. Signup and view all the answers

What type of molecule is sphingomyelin?

A non-glyceric phospholipid in cell membranes. Signup and view all the answers

What is the primary role of lipid signaling molecules such as steroid hormones?

To act as molecular messengers carrying signals within cells. Signup and view all the answers

What do glycolipids contribute to cell membranes?

They enhance membrane fluidity and play roles in cell signaling. Signup and view all the answers

What is the primary function of ATP within cells?

Main form of chemical energy Signup and view all the answers

What distinguishes polar amino acids from nonpolar amino acids?

Polar amino acids are hydrophilic and tend to be on the outside of proteins Signup and view all the answers

Which statement about the peptide bonds between amino acids is accurate?

They link the alpha-carboxyl group of one amino acid to the alpha-amino group of another Signup and view all the answers

What is the significance of the N-terminal and C-terminal ends of a polypeptide?

They denote the direction of protein synthesis Signup and view all the answers

Why are proteins considered the most varied macromolecules?

They perform a wide range of functions across different processes Signup and view all the answers

What role do proteins play in the immune response?

They provide defenses against infection Signup and view all the answers

How did Frederick Sanger contribute to the understanding of proteins in 1953?

He was the first to determine the complete sequence of a protein Signup and view all the answers

What aspect of proteins is primarily responsible for their function?

Their characteristic three-dimensional configurations Signup and view all the answers

What defines the primary structure of proteins?

The sequence of amino acids in a polypeptide chain Signup and view all the answers

Which of the following describes the secondary structure of proteins?

The structured arrangement of localized regions of amino acids Signup and view all the answers

What crucial role do hydrogen bonds play in protein structures?

They maintain secondary structures. Signup and view all the answers

How do phospholipids contribute to the structure of cell membranes?

They form a double layer due to their fatty acid tails. Signup and view all the answers

What is the effect of temperature on the fluidity of lipid bilayers?

Fluidity increases with higher temperatures. Signup and view all the answers

Which structure is responsible for defining the internal compartments of eukaryotic cells?

Cell membranes Signup and view all the answers

What is one of the primary functions of membrane proteins?

They act as electron transporters and receptors. Signup and view all the answers

Which characteristic of lipid bilayers is crucial for their function?

Their ability to behave like fluids. Signup and view all the answers

Study Notes

Unit 2: Molecules and Membranes

This unit introduces the fundamental molecules and membranes within cells.

Section 1: Introduction

Molecules and membranes are key components of cells.

Index

2.1 Cell Molecules:
- Carbohydrates (sugars)
- Lipids (fats)
- Nucleic acids (DNA, RNA)
- Proteins
2.2 Cell Membranes:
- Membrane lipids (phospholipids, glycolipids, cholesterol)
- Membrane proteins (integral and peripheral)
- Transport across cell membranes (passive and active)

2.1 Cell Molecules

Cells are complex structures with specialized functions.
Cells are composed of water, inorganic ions, and organic molecules (containing carbon).

Water

Water accounts for a significant percentage (70% or more) of cell mass.
Water is a polar molecule with slightly positive hydrogen atoms and a slightly negative oxygen atom.
This polarity allows water to form hydrogen bonds with other polar molecules and charged ions.
Water molecules interact with polar molecules (hydrophilic), while nonpolar molecules (hydrophobic) do not interact well with water.

Inorganic Ions

Inorganic ions represent a smaller percentage (1% or less) of cell mass.
These ions play critical roles in cellular functions and metabolism.
Examples include sodium (Na+), potassium (K+), magnesium (Mg2+), calcium (Ca2+), chloride (Cl-), hydrogen phosphate (HPO42-), and bicarbonate (HCO3-).

Organic Molecules

Organic molecules make up over 90% of the dry weight of most cells.
The molecules are diverse, including carbohydrates, lipids, proteins, and nucleic acids.
Macromolecules are formed by polymerizing smaller precursors (monomers).

Carbohydrates

Simple sugars (monosaccharides): Main cellular nutrients with energy functions.
Polysaccharides: These are structural components and energy storage forms.
Examples include glycogen (animal cells) and starch (plant cells).
Cellulose provides structural support in plant cell walls.

Monosaccharides

The basic formula is (CH2O)n, where n is the number of carbons.
Glucose is a primary source of energy in cells.
Other monosaccharides have between 3-7 carbons.
Sugars with 5 or more carbons often form ring structures in cells.
Glucose exists in two forms, α and β, depending on the placement of the hydroxyl group on C1.

Glycosidic Bonds

Monosaccharides link together through dehydration reactions to form polysaccharides.
The resulting bonds are glycosidic bonds.
If only a few sugars are attached, the resulting polymer is called an oligosaccharide
Polymers of hundreds or thousands of sugars are called polysaccharides.

Glycogen and Starch

Glycogen is the storage form of carbohydrates in animals.
Starch stores carbohydrates in plants
Both glycogen and starch are composed of glucose molecules.
Glycogen is more highly branched than starch.

Cellulose

Cellulose is a structural component of plant cells (cell walls).
It consists of glucose molecules linked by β (1→4) glycosidic bonds.
Straight chains of cellulose molecules are packed together to form strong fibers that provide structural integrity.

Lipids

Lipids are mainly composed of hydrocarbon chains with a carboxyl group.
Fatty acids (the simplest lipids) contain long hydrocarbon chains and a carboxyl group.
Triglycerides are energy storage molecules formed from glycerol and fatty acids.
Cell membranes are composed primarily of phospholipids (composed of fatty acids, glycerol, and a phosphate group).

Phospholipids

Phospholipids are amphipathic molecules: both hydrophobic and hydrophilic, forming cell membranes.
Hydrophobic tails of the phospholipids orient inward, and the hydrophilic heads face outward.
Phospholipids form a bilayer, with the hydrophobic tails facing each other and the hydrophilic heads contacting the aqueous environment.
The phospholipid bilayer is responsible for compartmentalization within cells.

Cholesterol

Cholesterol is a component of animal cell membranes.
It has a steroid structure differing from phospholipids in that it contains a fused ring structure.
Cholesterol affects the fluidity of the membrane, preventing excessive rigidity at low temperatures and excessive fluidity at high temperatures

Nucleic Acids

Nucleic acids are the primary information carriers of cells.
DNA (deoxyribonucleic acid) is the blueprint of genetic material in most organisms.
RNA (ribonucleic acid) is involved in protein synthesis.
RNA comes in different types (mRNA, rRNA, tRNA), each with specific functions.

Nucleotides

Nucleotides are the building blocks of nucleic acids.
Nucleotides consist of a nitrogenous base, a sugar (deoxyribose or ribose), and a phosphate group.
Purines (adenine and guanine) and pyrimidines (cytosine, thymine, and uracil) are examples of nitrogenous bases

Proteins

Proteins are a diverse group of macromolecules performing essential tasks in the cell.
Proteins are polymers of amino acids connected by peptide bonds.
Amino acids have 20 different types; their properties (polar, nonpolar, acidic, basic) affect protein structure and function.

Protein Structure

Primary: The amino acid sequence of a polypeptide chain.
Secondary: Hydrogen bond formation between amino acid backbones (alpha helix, beta sheet).
Tertiary: The three-dimensional folding of the polypeptide.
Quaternary: Multiple polypeptide chains interacting to form a functional protein complex.

Cell Membranes

Cell membranes separate the inside of the cell from its surroundings.
All cell membranes are composed of a phospholipid bilayer and proteins embedded within it.
The phospholipid bilayer regulates the passage of substances across the membrane.

Membrane Proteins

Integral proteins are embedded in the lipid bilayer, often spanning the entire width of the membrane forming channels or carriers that help move substances across the membrane.
Peripheral proteins are associated with the membrane surface (inside or outside)

Transport Across Membranes

Passive transport involves the movement of molecules from an area of high concentration to an area of low concentration (along a concentration gradient).
Active transport involves the movement of molecules against a concentration gradient using energy (ATP).
Membrane proteins (channels and carriers) assist in transport across membranes.

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Description

Explore the fundamental molecules and membranes that make up cells in this quiz. Learn about key components such as carbohydrates, lipids, nucleic acids, and proteins. Understand the structure and function of cell membranes and the importance of water within cells.