Biology Unit 2: Molecules and Membranes

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Questions and Answers

What do polysaccharides and shorter sugar polymers primarily act as in cells?

Energy sources

Structural components of membranes

Markers for cell recognition processes (correct)

Transporters for lipid molecules

Which of the following sugars is primarily considered the main source of energy in cells?

Galactose

Fructose

Glucose (correct)

Sucrose

What type of bond connects monosaccharides in an oligosaccharide?

Hydrogen bond

Glycosidic bond (correct)

Ionic bond

Peptide bond

What differentiates amylopectin from amylose in starch?

Amylopectin has more branches. Signup and view all the answers

Which configuration is present in cellulose regarding its glucose residues?

b-configuration Signup and view all the answers

What kind of bonds primarily form the structure of cellulose?

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

Which of the following correctly describes the relationship between glycogen and starch?

Glycogen serves as a storage form in animals, while starch serves in plants. Signup and view all the answers

What is the primary role of carbohydrates in cell signaling?

As markers for protein direction Signup and view all the answers

What is the primary function of fatty acids in cells?

Energy source and components of membranes Signup and view all the answers

What characterizes the structure of triglycerides?

Three fatty acids linked to a glycerol molecule Signup and view all the answers

Why are triglycerides more efficient for energy storage than carbohydrates?

They produce more energy per weight than carbohydrates. Signup and view all the answers

What distinguishes phospholipids from triglycerides?

Phospholipids contain a polar head group. Signup and view all the answers

What role do steroids play in biological systems?

They act as molecular messengers for signaling. Signup and view all the answers

What defines the amphipathic nature of phospholipids?

They have both hydrophilic and hydrophobic regions. Signup and view all the answers

Which of the following is the main component of cell membranes?

Phospholipids Signup and view all the answers

Which type of lipid acts as a messenger carrying signals from receptors within cells?

Steroid hormones Signup and view all the answers

What is the primary role of ATP in cells?

It serves as the main form of chemical energy. Signup and view all the answers

Which of the following best describes the composition of amino acids?

Every amino acid has a carbon, an amino group, and a unique side chain. Signup and view all the answers

In protein structure, what do the terms N-terminal and C-terminal refer to?

The specific ends of polypeptide chains. Signup and view all the answers

How do polar amino acids interact with water?

They dissolve easily in water due to their hydrophilic properties. Signup and view all the answers

What defines the characteristic sequence of amino acids in a polypeptide?

The direction of synthesis from N-terminus to C-terminus. Signup and view all the answers

Which of the following functions do proteins NOT perform?

They store genetic information. Signup and view all the answers

What structural feature of cholesterol contributes to its amphipathic nature?

Hydroxyl group (OH) Signup and view all the answers

Frederick Sanger is known for determining the first complete sequence of which protein?

Insulin Signup and view all the answers

Which type of RNA is directly responsible for conveying genetic information from DNA to ribosomes?

Messenger RNA (mRNA) Signup and view all the answers

Which type of amino acids are usually found on the surface of proteins?

Hydrophilic basic and acidic amino acids Signup and view all the answers

What bond is formed during the polymerization of nucleotides to create nucleic acids?

Phosphodiester bonds Signup and view all the answers

In what direction are polynucleotides synthesized?

5' to 3' Signup and view all the answers

What is a characteristic of DNA's structure?

Complementary bases form hydrogen bonds Signup and view all the answers

Which of the following best describes oligonucleotides?

Small polymers with only a few nucleotides Signup and view all the answers

What are the nitrogenous bases found in DNA?

Adenine, thymine, cytosine, guanine Signup and view all the answers

How are cells signaled by testosterone and estradiol?

As hormones derived from cholesterol Signup and view all the answers

What role does cholesterol play in the lipid bilayer?

It increases membrane rigidity while maintaining fluidity at low temperatures. Signup and view all the answers

Which of the following statements best describes integral membrane proteins?

They are embedded in the lipid bilayer and can be transmembrane proteins. Signup and view all the answers

What describes the primary function of peripheral membrane proteins?

They are indirectly associated with membranes through interactions with other proteins. Signup and view all the answers

What is the characteristic feature of transmembrane proteins?

They pass through the membrane multiple times or are fully embedded. Signup and view all the answers

Which types of molecules can freely diffuse through the phospholipid bilayer?

Small uncharged molecules. Signup and view all the answers

What best defines the function of protein channels in the membrane?

They facilitate the passage of charged ions and specific small molecules. Signup and view all the answers

How do carbohydrates modify membrane proteins in eukaryotic cells?

By forming glycoproteins exposed on the cell surface for signaling. Signup and view all the answers

Which substances are likely unable to diffuse across the plasma membrane?

Large polar molecules such as glucose. Signup and view all the answers

What defines the primary structure of a protein?

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

Which type of bond is primarily responsible for maintaining the secondary structure of proteins?

Hydrogen bonds Signup and view all the answers

What characterizes the quaternary structure of proteins?

Interactions between different polypeptide chains Signup and view all the answers

What is the main function of membrane proteins?

Facilitate the transport of small molecules Signup and view all the answers

What primarily influences the fluidity of a lipid bilayer?

The temperature of the environment Signup and view all the answers

Which property of phospholipids allows them to form bilayers in aqueous solutions?

Amphipathic nature of the molecules Signup and view all the answers

How do the properties of lipid bilayers change based on temperature?

Short chain fatty acids increase fluidity at lower temperatures Signup and view all the answers

What structural feature is common to all cell membranes?

Phospholipid bilayers Signup and view all the answers

Study Notes

Unit 2: Molecules and Membranes

This unit discusses the molecules and membranes within cells.
It details the fundamental components of cells and their roles in cellular functions.

Section 1: Introduction

This section introduces the topic of molecules and membranes within the context of cells.
It provides the overall framework for studying cellular components.

2.1 Cell Molecules

Cells are complex, diverse structures within multicellular organisms.
They are primarily composed of water, inorganic ions, and organic molecules.
Key elements present in significantly high concentrations in the human body (96.2%): oxygen, hydrogen, carbon, and nitrogen.

2.1.1 Water

Water makes up 70% (or more) of the cell mass.
It is a polar molecule, meaning its hydrogen atoms have a slightly positive charge and the oxygen atom has a slightly negative charge.
This polarity allows water to form hydrogen bonds and interact with polar molecules or ions.
Ions and polar molecules dissolve easily in water (hydrophilic), while nonpolar molecules are insoluble (hydrophobic).

2.1.2 Inorganic Ions

Inorganic ions, like sodium (Na+), potassium (K+), magnesium (Mg2+), calcium (Ca2+), and chloride (Cl-), represent 1% (or less) of the cell's mass.
These ions play a crucial role in cellular metabolism and various cellular functions.
Examples include phosphate (HPO42-), bicarbonate (HCO3-), amongst others.

2.1.3 Organic Molecules

Organic molecules (containing carbon) make up over 90% of the dry weight of cells.
Four main types include carbohydrates, lipids, proteins, and nucleic acids.
Precursors of these macromolecules have smaller molecules like amino acids, nucleotides, or simple sugars

2.2 Cell Membranes

Cell membranes delimit the interior of the cell from its environment.
Membranes share the same phospholipid bilayer structure.
Proteins play important roles within the bilayer.

2.2.1 Membrane Lipids

Phospholipids are the fundamental molecules of cell membranes.
Their hydrophobic tails (insoluble in water) spontaneously form bilayers in aqueous media.
They form a stable barrier between aqueous environments.
Lipids typically constitute about 50% of the cell membrane, but this can vary based on the type (up to 75% in mitochondria).

2.2.2 Membrane Proteins

Membrane proteins are integral components of cell membranes performing specialized functions.
Integral proteins can be transmembrane (spanning the membrane) or embedded within the bilayer.
Peripheral proteins are not embedded, but interact with the membrane indirectly.
Other proteins include glycoproteins (proteins with carbohydrate chains) and glycolipids (lipids with carbohydrate chains).

2.2.3 Transport Across Cell Membranes

Membranes selectively allow molecules to pass through them.
Small uncharged molecules can diffuse easily through the phospholipid bilayer.
Larger polar molecules and charged ions need specific transport mechanisms (protein channels or carrier proteins).
Passive transport occurs down the concentration gradient using protein channels or carrier proteins.
Active transport occurs against the concentration gradient and requires energy (ATP).

2.2.4. Other Functions of Carbohydrates

Carbohydrates function as markers in cell signaling and cell-cell interactions.
They are involved in interactions between cells in multicellular tissues.
They can be found in glycoproteins (proteins with carbohydrate chains) and glycolipids (lipids with carbohydrate chains).

2.3 Nucleic Acids

Nucleic acids are the main information molecules of cells.
DNA (deoxyribonucleic acid) is the genetic material.
RNA (ribonucleic acid) comes in various forms like messenger RNA (mRNA), ribosomal RNA (rRNA), and transfer RNA (tRNA), each having specific roles in protein synthesis.
Nucleotides (nitrogenous bases, sugars, and a phosphate group) are the building blocks of nucleic acids.
Purines (adenine and guanine) and pyrimidines (cytosine, thymine, and uracil) are the nitrogenous bases.

2.4 Proteins

Proteins perform diverse functions within cells.
They have varied macromolecular structures.
Proteins are composed of amino acids (aa).
Twenty different amino acids (aa) exist.
Amino acids are linked by peptide bonds.
Protein structure is described in four levels (primary, secondary, tertiary, and quaternary).
Proteins' specific function relies on their three-dimensional shapes.
A protein's function and interaction with other biological components depend on its amino acid sequence.

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Description

This quiz explores Unit 2 of Biology, focusing on molecules and membranes within cells. You'll learn about the fundamental components of cells, including the significance of water, inorganic ions, and organic molecules in cellular functions.