Ch. 3 Proteins Flashcards
The “first in rank” macromolecules.
Proteins
-in ending reflects the presence of _______.
Amino groups
_____ from amino groups contributes significantly to protein mass (16% on average).
Nitrogen
Two key aspects of proteins
- structure: from building blocks to three-dimensional shape
- function: diverse roles in biological systems
Proteins are composed of a limited set of ____ fundamental amino acids.
20
Modified amino acids exist but arise from the 20 fundamental ones after __________.
Protein synthesis
How many amino acids are essential?
8
How are essential amino acids obtained in the body?
Through the diet, because they cannot be synthesized through the body.
How many amino acids are “non-essential”?
12
How does the body synthesize the 12 non-essential amino acids?
Through compounds already present in our cells.
The general formula of amino acids includes:
central (alpha) carbon atom with 4 attached groups: carboxyl group COO-, amino group +H3N, hydrogen H, variable group (side chain) R.
Amino acids are ionized in _______ solutions.
Aqueous
What is an amino acid’s predominant form at physiological pH?
Neutral (zwitterionic)
Side chains vary in ______
Size, charge, polarity, and chemical reactivity
Amino acids link ____ to form proteins.
Covalently
Short stretches of amino acids are known as ________.
Peptides
Peptides are _______.
Proteins digested to produce shorter chains.
What indicates the number of amino acids in a peptide chain? Give 3 examples.
Prefixes - di, tri, tetra
What term describes 10-20 amino acids in a chain?
Oligopeptide
What term describes more than 20 amino acids in a chain?
Polypeptide
Proteins are often referred to as ________.
Polypeptide chains
How do peptide bonds form?
Via a synthesis condensation reaction, producing water.
How do peptide bonds break?
A hydrolysis reaction, requires the addition of water.
The left side of a Lewis structure is known as _______.
N-terminus
The right side of a Lewis Structure is known as _______.
C-terminus
What is a residue?
The part of the amino acid involved in peptide formation (what is left over after linking with others to become a larger polymer).
A free carboxyl group deriving from aspartate and a free amino group belonging to phenylalanine.
Dipeptide Asp-Phe (isomer of Phe-Asp)
What are the four levels of protein structures?
Primary, secondary, tertiary, and quaternary
The most basic level of protein structures.
Primary
Humans can have around ______ to ______ proteins.
100,000 to 200,000
Primary structure is determined by ________.
Genetic information in genes encodes the amino acid sequences.
3D arrangements within proteins, polypeptide chain folding in specific patterns.
Secondary structure
Key Players - Noncovalent with some covalent character; Forms between δ+(H) and δ-(O or N) atoms, because O and N have a higher electronegativity than H; Stabilizes the secondary structure.
Hydrogen Bonds
The two common types of secondary structures
Alpha (α) helix, Beta (β) sheet
Resembles a right-handed spiral staircase, backbone forms a spiral, side chains point outward, stabilized by hydrogen bonds between adjacent turns.
Alpha (α) Helix
Resembles a crinkled bedsheet, strands are segments of stretched polypeptide chain, strands undulate with parallel peptide unit planes, adjacent residue side chains point in opposite directions.
Beta (β) Sheet
Conformation of the entire polypeptide chain, flexible and can fold to bring distant residues together, stabilized by various (four) interactions.
Tertiary structure
4 different types of tertiary interactions
Electrostatic Bond, Van Der Waals Interaction, Disulfide Bond, Hydrophobic Interaction
Formed between oppositely charged groups; weaker than hydrogen bonds.
Electrostatic Bonds
Positively charged groups of electrostatic bonds
Terminal amino group, lysine, arginine, and possibly histidine
Negatively charged groups of electrostatic bonds
Terminal carboxyl group, aspartate, and glutamate
Noncovalent attraction due to electron movements, momentary asymmetries induce electrostatic forces, weaker than electrostatic bonds
Van Der Waals Interaction
Covalent bond between cysteine residues (sulfur atoms from two cysteine residues), forms through shedding of H atoms, stronger than peptide bonds, remains united as cystine after protein breakdown.
Disulfide bonds
Side chains (alanine, valine, leucine) cluster together, driven by repulsion by surrounding water, more stable than exposure to water, weakest interaction discussed
Hydrophobic Interaction
The process of altering a protein’s structure, causing it to unfold or break up.
Denaturation
Two main factors of leading to denaturation, provide 2 examples of this process.
High temperature and extreme pH values - cooking eggs, yogurt formation.
Why does high temperature lead to denaturation? Is it reversible or irreversible?
Thermal movement disrupts protein structure , alteration of the polypeptide chain - often irreversible.
Why do extreme pH values lead to denaturation? Is it reversible or irreversible?
Addition or removal of protons (H+) from chemical groups, affects hydrogen and electrostatic bonding - typically irreversible.
Consists of multiple polypeptide chains (known as subunits/simply chains), stabilized by the same bonds as tertiary structures.
Quaternary Structure
