Chemistry Chapter 5: Chemical Bonding

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Questions and Answers

What determines the chemical bonding properties of an atom?

  • The number of neutrons in the atom.
  • The number of orbitals surrounding the atom.
  • The number of protons in the atom.
  • The distribution of electrons and their charges. (correct)

Which of the following best describes the role of electrons in chemical bonding?

  • Electrons determine the atomic number of an element.
  • Electrons are only involved in forming covalent bonds.
  • Electrons are responsible for the mass of an atom.
  • Electrons are involved in the formation of both ionic and covalent bonds. (correct)

What is the defining characteristic of an isotope?

  • An isotope has a different number of neutrons compared to its original element. (correct)
  • An isotope has a different number of electrons compared to its original element.
  • An isotope has a larger atomic mass compared to its original element.
  • An isotope has a different number of protons compared to its original element.

What is the primary factor that governs the movement of electrons between atomic shells?

<p>The amount of energy absorbed or released by the atom. (C)</p> Signup and view all the answers

Which of the following elements would be considered essential for life as discussed in the text?

<p>Carbon (C) (A)</p> Signup and view all the answers

Atoms are most stable when they have...

<p>Paired electrons (B)</p> Signup and view all the answers

What is the significance of the term 'universal solvent' when applied to water?

<p>Water can dissolve a wide variety of substances due to its polar nature. (A)</p> Signup and view all the answers

Which type of bond is characterized by the sharing of electrons between atoms?

<p>Covalent bonds (B)</p> Signup and view all the answers

What is the primary type of bond responsible for determining the structure of proteins?

<p>Covalent bonds (D)</p> Signup and view all the answers

How does the presence of isotopes impact the field of carbon dating?

<p>The decay rate of carbon isotopes is used to date ancient materials. (B)</p> Signup and view all the answers

The text mentions 'membranes'. What is the fundamental function of these biological membranes?

<p>To act as barriers, controlling the passage of substances into and out of cells. (C)</p> Signup and view all the answers

Which type of bond is formed by the interaction between partial charges on polar molecules?

<p>Hydrogen bonds (A)</p> Signup and view all the answers

Water's ability to act as a universal solvent is primarily due to:

<p>Its ability to form hydrogen bonds (D)</p> Signup and view all the answers

The high specific heat of water is a result of...

<p>Hydrogen bonding (D)</p> Signup and view all the answers

Cohesive and adhesive properties of water are primarily attributed to:

<p>The formation of hydrogen bonds (B)</p> Signup and view all the answers

The polarity of water contributes to its ability to interact with which of the following types of compounds?

<p>Both charged and uncharged polar compounds (C)</p> Signup and view all the answers

Which of the following organelles is NOT part of the endomembrane system?

<p>Mitochondria (D)</p> Signup and view all the answers

What is the purpose of using GFP in plant cells?

<p>To visualize the structure and movement of organelles (B)</p> Signup and view all the answers

What is the role of SYP121 in the cell?

<p>It helps to transport proteins from the endoplasmic reticulum to the Golgi apparatus. (A)</p> Signup and view all the answers

What happens when GFP is co-transfected with SYP121ΔC in leaves?

<p>GFP accumulates in the endoplasmic reticulum and Golgi apparatus. (A)</p> Signup and view all the answers

What technique is used to visualize the dynamic movement of organelles in the cell?

<p>Fluorescence microscopy (C)</p> Signup and view all the answers

What is the role of the Golgi apparatus in the cell?

<p>To modify, package, and transport proteins and lipids. (B)</p> Signup and view all the answers

Which of the following organelles are NOT enclosed by a membrane?

<p>Ribosomes (D)</p> Signup and view all the answers

What is the process called when proteins move from the endoplasmic reticulum (ER) to the Golgi apparatus?

<p>Anterograde transport (C)</p> Signup and view all the answers

What is the primary function of membranes in cells?

<p>To compartmentalize metabolic activities (A)</p> Signup and view all the answers

What is the main reason why sucrose diffusion across membranes is very slow?

<p>Sucrose is a large molecule (B)</p> Signup and view all the answers

What is the term used to describe molecules like phospholipids that have both hydrophilic and hydrophobic regions?

<p>Amphipathic (D)</p> Signup and view all the answers

What is the Nernst Equation used to calculate?

<p>The equilibrium potential of a charged molecule (D)</p> Signup and view all the answers

What is the primary driving force for the diffusion of ions across a membrane?

<p>Both concentration and electrical gradients (B)</p> Signup and view all the answers

How does the biological membrane contribute to cellular energy generation?

<p>By creating ion gradients that drive ATP production (B)</p> Signup and view all the answers

What is the significance of voltage across cell membranes?

<p>It allows for the transmission of nerve impulses (A)</p> Signup and view all the answers

How can the voltage across endomembranes be measured?

<p>Using fluorescent dyes that are sensitive to voltage (B)</p> Signup and view all the answers

Flashcards

Atoms

Atoms are the smallest particles that retain the properties of an element.

Sub-atomic particles

Components of atoms: protons, neutrons, and electrons.

Atomic number

Determined by the number of protons in an atom.

Isotopes

Atoms of the same element with different numbers of neutrons.

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Chemical bonding

Interactions between atoms that result in the formation of compounds.

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Electron distribution

Electrons exist in shells and orbitals around the nucleus.

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Energy and electron movement

Electrons move between shells by absorbing or releasing energy.

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Membranes

Thin layers forming cell boundaries and supporting bioenergetics.

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Bonds

Connections formed when atoms share or exchange electrons to achieve stability.

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Ionic Bonds

Bonds formed when atoms exchange electrons, resulting in charged ions.

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Covalent Bonds

Bonds formed when atoms share electrons to fill their outer shells.

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Valence Electrons

Electrons in the outermost shell that determine bonding capacity.

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Hydrogen Bonds

Weak attractions between partially charged molecules, like water molecules.

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Polarity of Water

Water's distribution of charge, making it a universal solvent and enabling hydrogen bonding.

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Capillary Action

Movement of water through small spaces due to adhesive and cohesive forces.

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Hydration Shells

Layers of water molecules surrounding ions in solution, stabilizing them.

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Amphipathic molecules

Molecules with both hydrophilic (water-loving) and hydrophobic (water-fearing) parts.

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Phosphatidyl choline

A type of phospholipid with choline, phosphate linked to glycerol, and two fatty acids.

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Compartmentalization

Dividing cellular functions into distinct sections or compartments.

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Nernst Equation

Describes the equilibrium of chemical and electrical forces on an ion.

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Ion gradients

Differences in ion concentrations across membranes, crucial for biological energy.

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Diffusion rates

Speed at which substances, like sucrose, spread across membranes.

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Bioenergetics

The study of energy transformations in biological systems, utilizing ion gradients.

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Eukaryotic Organelles

Membrane-bound structures within eukaryotic cells that perform specific functions.

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Mitochondria

Organelles that generate ATP through cellular respiration; known as the powerhouse of the cell.

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Chloroplasts

Organelles that conduct photosynthesis, converting light energy into chemical energy in plants.

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Golgi Apparatus

An organelle that modifies, sorts, and packages proteins and lipids for secretion or delivery.

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Endoplasmic Reticulum (ER)

Network of membranes involved in protein and lipid synthesis; comes in rough and smooth types.

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Green Fluorescent Protein (GFP)

A protein that exhibits bright green fluorescence when exposed to light in the blue to ultraviolet range.

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Endocytosis

The process by which cells engulf external substances, taking them into the cell.

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Exocytosis

The process of exporting materials out of the cell by vesicles that fuse with the plasma membrane.

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Study Notes

Hands-On Summer-Break Research

  • The Dobbie Smith Prizes offer a £1000 bursary for a 6-8 week summer research experience.
  • Open to first-year natural sciences and related studies students at the University of Glasgow.
  • Students must consult with a suitable member of staff, agree on a project, and then submit an application letter to the Undergraduate School.
  • Details are available on the MOODLE site or from Prof. M. Blatt ([email protected]).
  • The deadline for applications is 12:00 noon on Friday, 28th March 2025.

Atoms, Bonds, Water, and Membranes

  • What are atoms?
    • Atoms are the smallest particles that retain the properties of an element (e.g., carbon, oxygen).
    • Atoms are made up of subatomic particles: protons, neutrons, and electrons.
    • Elemental properties are determined by the atomic number (number of protons).
    • Most atoms have equal numbers of protons and neutrons, but some isotopes may have additional neutrons (e.g., carbon-14).
  • What are bonds?
    • Bonds form when atoms share or exchange electrons to achieve more stable (full) electron shells.
    • Different bonds (ionic, covalent) form depending on how atoms transfer or share electrons.
  • Why is water a 'universal solvent'?
    • Water is a polar molecule (due to uneven electron distribution), meaning it has partial charges.
    • This polarity allows water to interact with other polar and charged molecules.
  • What are membranes?
    • Membranes are phospholipid polymers (made of fatty acids, glycerol, phosphate, and a terminal group).
    • Phospholipids are amphipathic molecules, meaning they have both hydrophilic and hydrophobic parts. This leads to spontaneously assembling monolayers and bilayers in water.
    • Membranes are crucial for compartmentalization within cells, protecting components, and enabling signal transduction.

What Determines Chemical Bonding?

  • The physical chemistry of an atom is determined by its electronic complement and the distribution of electrons around the nucleus.
  • Electrons are arranged in electron shells and orbitals, which define the probability distribution of that electron within shells and orbitals.
  • Electrons can move between shells, requiring an input or release of energy.

What Determines Bond Formation?

  • Bonds form when atoms share or exchange electrons to achieve stable or filled electron shells.
  • Stable atomic states possess paired electrons and filled electron shells.
  • Atoms with unpaired electrons or partially-filled outer shells react to fill or empty their shells.
    • Examples are given using the Lewis-dot representation.

Electron Shells Define the Periodic Table of Elements

  • Electron shells determine an elements position on the Periodic Table.
  • Elements with similar electron configurations share similar chemical properties and reactivity.

Which Bonds are Important for Life?

  • Ionic Bonds:
    • Form when atoms exchange electrons.
    • Result in oppositely charged ions that attract each other forming an ionic bond, like in sodium chloride.
    • Crucial in biological processes, such as forming crystals and for transporting ions within the cell.
    • Atomic valence differs from ionic valence.
  • Covalent Bonds:
    • Form when atoms share electrons.
    • Examples are given, including hydrogen, water, and methane.
    • Different covalent bond types (single, double, triple bonds) are defined by the number of electrons shared.
  • Hydrogen Bonds:
  • Partial charge interactions between polar molecules.
    • Important for interactions between water molecules.
  • Van der Waals Interactions:
    • Interactions that arise between atoms with locally induced dipoles, very close together.

Why is Water a 'Universal Solvent' for Life?

  • Water molecules are polar; they possess a partial positive charge on hydrogen, and a partial negative charge on oxygen.
  • These interactions allow water to readily dissolve polar (charged) and ionic compounds, creating hydration shells around them.
  • This high polarity and tendency to form hydrogen bonds also explains water's cohesive and adhesive properties, high specific heat, and role as a good insulator.

Adhesive/Cohesive Forces in Wetting and Capillary Action

  • Cohesion refers to the attraction between water molecules.
  • Adhesion refers to the attraction between water molecules and other molecules.
  • These forces are crucial for water transport and plant transpiration.
  • Cohesive tension limits tree size due to how water moves upward through the stem

Biological Membranes Hold Charge

  • Diffusion of Ions:
    • Driven by chemical and electrical gradients.
  • Selective Diffusion:
    • Across semi-permeable membranes creates a small ion imbalance.
  • The Nernst Equation:
    • Describes the equilibrium between chemical & electrostatic forces on charged molecules (ions).
  • Electrode Use:
    • Microelectrodes can be used to measure membrane voltage.

Organelles and Their Locations

  • A variety of organelles is present to separate different roles and protect various components, and include:
    • Nucleus
    • Rough endoplasmic Reticulum
    • Smooth endoplasmic Reticulum
    • Golgi
    • Mitochondria
    • Chloroplasts
    • Lysosomes
  • These organelles are membrane-bound and contribute to both structural and functional compartmentalization.

What Are Membranes?

  • Membranes are phospholipid bilayers.
  • Phospholipids are amphipathic (hydrophilic head, hydrophobic tails).
  • These molecules spontaneously form monolayers and bilayers in water.
  • Simple detergents function as amphipathic molecules and are able to dissolve other polar and organic compounds in water.

Why Are Membranes Important?

  • Membranes compartmentalize metabolic activities.
  • Membranes separate and protect cellular components.
  • Membranes provide a scaffold for signalling components.
  • Membranes act as a medium for cellular energy generation (e.g., electron transport chain).
  • Diffusion across membranes is important for transporting molecules between the inside and outside of cells.

What Do Diffusion Rates Mean?

  • Diffusion rates across membranes are influenced by factors like distance, concentration gradients, and the size of the diffusing molecules.
  • Diffusion is slower in thicker membranes than thinner ones.
  • Limits cell & membrane size in biological materials.

Fluorescence - A New Window on the Cell

  • Fluorescence occurs when a molecule absorbs light, causing electrons to move to an excited state.
  • Energy is then released when the electrons return to their ground state, resulting in the emission of light at a longer wavelength.
  • This enables cell analysis and is used to investigate details of cell structure and function

Green Fluorescent Protein (GFP)

  • GFP is a protein that fluoresces when exposed to light.
  • Genetically engineered GFP can be used to visualize cell processes and structures in plants and animals.

Endoplasmic Reticulum

  • ER is a network of membranes within cells involved in protein synthesis and processing and other tasks. This network is highly mobile within the cell.
  • ER is interconnected by membranes.

Golgi

  • Golgi is organized in stacks and/or networks of membrane sacs that process, modify, and transport proteins.
  • Similar to ER, the Golgi also appears to be highly mobile within the cell.
  • Both plant and animal cells have similar Golgi structures.

Chloroplasts

  • Chloroplast are plant organelles that carry out photosynthesis.
  • Chloroplasts and mitochondria have double membranes, suggesting a symbiotic origin.
  • Chloroplasts have their own independent division and replication mechanisms.
  • Chloroplasts can communicate within cells by creating structures called Stromules.

Membrane Structure and Function

  • Membranes are phospholipid polymers that spontaneously form monolayers and/or bilayers in water.
  • Membranes function as physical barriers and support structures within the cell.
  • Organelles, including ER, Golgi, mitochondria and chloroplasts are membrane-enclosed compartments crucial for eukaryotic cell function.

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