Biological Chemistry 1: Elemental Composition of Cells

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Questions and Answers

Why is the Si-Si bond weaker than the C-C bond?

Silicon atoms are more electronegative than carbon atoms.

Silicon atoms have a lower electronegativity than carbon atoms.

Silicon has a larger atomic radius than carbon. (correct)

Silicon atoms are more reactive than carbon atoms.

Why are extended chains of nitrogen atoms unstable?

Nitrogen atoms readily form ionic bonds.

Nitrogen atoms are too electronegative to form stable bonds.

Nitrogen atoms have a lone pair of electrons that repel each other. (correct)

Nitrogen atoms have a low ionization energy.

Which of the following reasons explains why silicon is not commonly incorporated in living cells, despite its abundance?

Silicon is less reactive than carbon.

Silicon is a radioactive element.

Silicon forms strong bonds with oxygen, making it inert. (correct)

Silicon is toxic to living organisms.

What is the primary reason for the instability of boron compounds?

Boron atoms form electron-deficient compounds. (A) Signup and view all the answers

Which of the following is NOT a reason why certain elements are not incorporated in living organisms?

The abundance of the element in the Earth's crust. (B) Signup and view all the answers

What is the main reason for the preferential incorporation of carbon in living cells over silicon, despite the higher abundance of silicon?

Carbon can form more diverse and complex molecules, essential for biological functions. (B) Signup and view all the answers

Which of the following is NOT true about nitrogen's role in biochemistry?

Nitrogen forms stable extended chains of atoms. (B) Signup and view all the answers

What is a common characteristic of elements not found in living organisms, despite their potential usefulness?

They are artificially synthesized elements. (B) Signup and view all the answers

Which of the following is NOT a characteristic of the major elements (CHONPS) found in living cells?

They tend to form ionic bonds. (A) Signup and view all the answers

What is the primary mechanism for the formation of elements heavier than iron (Fe)?

Neutron capture during a supernova. (A) Signup and view all the answers

Why is carbon considered unique in its ability to form a vast array of compounds?

Carbon can form stable chains and rings with itself and other elements. (A) Signup and view all the answers

Which of the following elements is considered a trace element, found in the fluids surrounding cells?

Magnesium (Mg) (B) Signup and view all the answers

What is the primary reason for the relative abundance of even-numbered elements compared to odd-numbered elements?

Even-numbered elements are more abundant in the universe due to how they are formed in stars. (D) Signup and view all the answers

Which of the following is a transuranium element, synthesized in a laboratory?

Californium (Cf) (C) Signup and view all the answers

What is the significance of the observation that the concentration of certain ions in seawater is similar to that in blood plasma?

It indicates the importance of these ions for maintaining cellular function and homeostasis. (C) Signup and view all the answers

Based on the provided information, which element is most abundant in the Earth's crust?

Oxygen (O) (B) Signup and view all the answers

Which of the following elements were formed primarily through the Big Bang?

Hydrogen and Helium (C) Signup and view all the answers

What condition is essential for fusion reactions in stars?

High temperature and pressure (A) Signup and view all the answers

Which of the following describes the process that occurs when a star runs out of hydrogen fuel?

The star collapses and heats up, initiating helium fusion. (B) Signup and view all the answers

Which of the following is NOT a direct product of helium fusion?

Magnesium (24Mg) (D) Signup and view all the answers

Why is beryllium (8Be) unstable?

It has a low binding energy per nucleon. (C) Signup and view all the answers

What is the primary reason why a star explodes as a supernova?

The star's core collapses under its own gravity, leading to a massive release of energy. (C) Signup and view all the answers

What is the primary source of light emitted by most visible stars?

Burning of hydrogen to form helium. (A) Signup and view all the answers

Which of the following processes is NOT involved in the formation of elements in stars?

Alpha decay (B) Signup and view all the answers

Study Notes

Biological Chemistry 1 (BIOL 157) - Lecture 1: Elemental Composition of Cells

Study Objectives: This lecture covers the origin of elements, the elements in living cells, why some elements are in cells and others are not, and why carbon forms so many compounds.

Introduction

All living cells and organisms are composed of intricately organized elements that form characteristic structures. Atoms combine to form molecules, which form cells, tissues, organs, organ systems, and finally, the organism.

Origin of Elements

Elements are formed through various processes:
- Big Bang
- Fusion reactions in stars,
- Artificial synthesis.

The Big Bang Theory

An infinitely hot and dense primordial matter exploded, forming hydrogen and helium.
Gravity brought together gas clouds, forming vast galaxies and billions of stars.
Elements beyond hydrogen and helium were formed in the centers of stars and released upon their explosions.

Fusion Reactions in Stars

Extremely high temperatures in stellar cores are necessary for fusion reactions.
High temperatures overcome electrostatic repulsion between positively charged nuclei, allowing them to fuse.
Fusion reactions produce heat and light, contributing to the formation and lifetime of stars.
An enormous amount of energy is released during these reactions, leading to star explosions.

Elements Formed in Stars

Hydrogen fusion forms helium.
Helium fusion forms beryllium, then carbon, then oxygen.
Iron is the largest atom formed by fusion.

Larger Elements Formation

Elements larger than iron are formed when neutrons from exploding stars are captured by iron nuclei.

Laboratory Synthesis of Elements

Elements with atomic numbers greater than 92 (transuranium elements) are artificially synthesized using high-energy particles in cyclotrons to fuse target nuclei. For example, Californium was made this way.

Elements in Living Cells

Not all elements found on Earth are found in cells. (Less than a third).
Percentage of atoms on earth: Oxygen (48.86%) Iron (18.84%) Silicon (13.96%) Magnesium (12.42%)
Percentage of carbon in cells is around 0.10 %
There's a similarity in the concentration of main ions in seawater and blood plasma (Cu²⁺, Mg²⁺, Ca²⁺, Na⁺, K⁺, etc.)
Living cells utilize CHONPS (Carbon, Hydrogen, Oxygen, Nitrogen, Phosphorus, Sulfur) for many organic molecules.
Trace elements (those not CHONPS) are sometimes necessary components of biological systems, and are usually found in cell fluids.

Striking Features of Major Elements in Cells

Primarily p-block elements
Their ability to form covalent bonds, being non-metals.
Their relatively small atomic sizes/numbers.
Not overly reactive nor inert.

Why Carbon Forms Many Compounds

Carbon's ideal size allows for stable covalent bonding.
It's tetravalent, meaning it can form four bonds.
Carbon has the power of catenation—forming chains with itself.
Carbon can form multiple bonds.

Other Elements with Bonding Capabilities

Silicon is tetravalent and can form chains like carbon. However, Si-Si bonds are rare, and Si-O bonds are very stable. Silicon is substantially more abundant than carbon in the Earth's crust, but carbon is preferentially incorporated in living cells.

Nitrogen Properties

Nitrogen forms N-N bonds with less energy than C-C bonds. N atoms have lone pairs which repel during bond formation, and this reduces overall bond energy. This makes extended nitrogen chains unstable.

Boron Properties

Boron has three valence electrons; it forms electron-deficient compounds, limiting the stability of boron compounds.

Reasons for Excluding Certain Elements

Artificial nature
Inert nature
Toxicity
Radioactivity

Non-Essential Elements with Beneficial Uses

Some elements, though not essential for life, can be valuable (e.g., Lithium for schizophrenia treatment, platinum/gold for cancer/arthritis treatments, Kaolin for diarrhea).

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Description

Explore the foundational concepts of Biological Chemistry in this lecture. Learn about the origin of elements, their presence in living cells, and the significance of carbon in forming various compounds. Ideal for students in BIOL 157 who want to deepen their understanding of cellular composition.