Biochemistry W2-1

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Questions and Answers

What is the primary reason for nonpolar molecules being poorly soluble in water?

They do not form hydrogen bonds with water molecules. (correct)

They have a higher density than water.

They disrupt the ionic interactions in water.

They have stronger hydrogen bonds than water.

Which of the following accurately describes a characteristic of covalent bonds?

They are generally weaker than noncovalent bonds.

They are formed between ions of opposite charges.

They can easily be broken and reformed in water.

They involve the sharing of electron pairs between atoms. (correct)

Which type of non-covalent bond is primarily responsible for the unique properties of water?

Ionic bonds

Van der Waals forces

Covalent bonds

Hydrogen bonds (correct)

Considering the formation of a phosphate group, which of the following best describes the molecular structure?

A structure consisting of one phosphorus atom and four oxygens. Signup and view all the answers

Which of the following types of non-covalent bonds is characterized by transient dipole-induced dipole interactions?

Van der Waals forces Signup and view all the answers

What is the concentration of H+ and OH- when H2O is 55 M and Keq = 1.8 x 10^-14 M?

H+ = 1.34 x 10^-7 M, OH- = 1.34 x 10^-7 M Signup and view all the answers

Which amino acid behaves similarly to tyrosine regarding its protonation states with pH changes?

Histidine Signup and view all the answers

What is the pKa value of acetic acid, indicating its strength as a weak acid?

4.76 Signup and view all the answers

What is the effect of adding NaOH during the titration of acetic acid?

It leads to the formation of a buffer solution. Signup and view all the answers

What happens when HCl is added to a solution of acetic acid?

The concentration of acetic acid decreases. Signup and view all the answers

What does pKa signify in the context of acid dissociation?

It's a logarithmic scale representing the strength of an acid. Signup and view all the answers

Why is maintaining intracellular pH crucial for all cells?

It keeps functional groups in the correct ionization state for their roles. Signup and view all the answers

What role does water typically play in hydrolysis reactions?

Water functions as a reactant. Signup and view all the answers

What occurs at an incorrect pH regarding enzyme-catalyzed reactions?

Enzymes become denatured, losing their functionality. Signup and view all the answers

What is the main purpose of buffering in biological systems?

To maintain a consistent pH despite changes in concentration. Signup and view all the answers

How does diabetes contribute to high blood ketone levels?

Through impaired insulin function leading to fat metabolism. Signup and view all the answers

Which factor most directly impacts gas exchange between CO2 gas and dissolved HCO3- in the blood?

pH balance in the blood. Signup and view all the answers

During titration, what is indicated by the pKa values on a titration curve of phosphoric acid?

The points at which the acid donates protons. Signup and view all the answers

Which biological process is impacted by the solubility of polar molecules?

Hydrogen bond formation among cellular components. Signup and view all the answers

Study Notes

Noncovalent Bonds/Interactions

Noncovalent bonds are weaker than covalent bonds
Noncovalent bonds are important for biological systems
They are responsible for the structure and function of macromolecules, such as proteins and DNA

Types of Noncovalent Bonds

Hydrogen Bonds:
- Occur between a hydrogen atom covalently linked to a highly electronegative atom (O, N, or F) and an electronegative atom on another molecule
- Contribute to the structure of water and proteins
Ionic Interactions:
- Occur between oppositely charged ions
- Important in the formation of salts and in the interaction of proteins with other molecules
Van Der Waals Interactions
- Occur between all molecules
- Result from temporary fluctuations in electron distribution that create transient dipoles
- Weak but significant, especially in large molecules
Hydrophobic Interactions:
- Occur between nonpolar molecules in an aqueous environment
- Water molecules form hydrogen bonds with each other, excluding nonpolar molecules
- Driving force behind the folding of proteins and the formation of membranes

Why are Nonpolar Molecules Poorly Soluble in Water?

Water is a polar molecule due to the electronegativity difference between oxygen and hydrogen.
Nonpolar molecules lack charged regions or polar groups, making them incapable of forming hydrogen bonds with water molecules.
The hydrophobic effect drives nonpolar molecules to minimize contact with water.
This leads to their clustering together and poor solubility in water.

Water Dissociation

The concentration of H+ and OH- can be calculated using the Keq value and the concentration of H2O:
- [H+] = [OH-] = √(Keq x [H2O])
- If the concentration of water is 55 M and the Keq is 1.8 x 10^-14 M, then the concentration of H+ and OH- is: 1 x 10^-7 M

pH of Human Body

The pH of human blood is slightly alkaline, around 7.35 to 7.45
It is maintained through a complex buffering system involving bicarbonate ions and other buffers

Tyrosine

Tyrosine is an amino acid that can exist in protonated and deprotonated forms
The protonated form has a positive charge on the amino group and a neutral carboxyl group
The deprotonated form has a neutral amino group and a negative charge on the carboxyl group
The transition form has a positive charge on the amino group, a negative charge on the carboxyl group, and a neutral side chain

pKa and Acids

pKa is the negative logarithm of the acid dissociation constant (Ka)
A lower pKa value indicates a stronger acid
Acetic acid is a weak acid with a pKa of 4.76

Titration of Acetic Acid with NaOH

Adding NaOH (a strong base) to acetic acid (a weak acid) will neutralize the acid
The pH will increase gradually as NaOH is added
At the equivalence point, the pH will jump significantly as all the acetic acid has been neutralized by the NaOH
At the equivalence point, the solution will consist mainly of the acetate ion conjugate base, which has a basic character

Titration of Acetic Acid with HCl

Adding HCl (a strong acid) to acetic acid (a weak acid) will cause the pH to decrease
The decrease in pH will be less significant than the increase seen when NaOH is added
HCl will protonate the acetate ion conjugate base, shifting the equilibrium towards the formation of acetic acid

Weak Acids

Water often participates in biological reactions
Condensation reactions produce water
Hydrolysis reactions use water

Dissociation of Weak Electrolytes

Acetic acid is an example of a weak electrolyte

Buffering

Buffering is essential to maintain intracellular pH.
Enzyme-catalyzed reactions have optimal pH.
Polar molecule solubility is dependent on hydrogen bond donors and acceptors
Maintaining the correct pH is important for gas exchange.
When pH is incorrect, functional groups are not in the correct ionization state to perform their role.
Many reactions occur within a narrow pH range and perform optimally at a specific pH.
Important biological buffer systems exist.

Metabolic Acidosis and Hypoventilation

Integrate knowledge with other disciplines.

Diabetes and Blood Ketones

Diabetes can lead to high levels of blood ketones.
High blood ketone levels can cause symptoms like fatigue, nausea, and rapid breathing.

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Description

Explore the different types of noncovalent bonds, including hydrogen bonds, ionic interactions, van der Waals interactions, and hydrophobic interactions. Understand their significance in biological systems and their role in the structure and function of macromolecules such as proteins and DNA.