Module 1: Cell Types, Nutrition, and Biomolecules

Flashcards covering cell types, Gram staining, organelle functions, nutrient requirements, growth media, cellular biomolecules, DNA/RNA structure, replication, and translation from Module 1.

What are the three classifications of cells based on oxygen tolerance?

Aerobic cells need oxygen to grow, anaerobic cells cannot grow in the presence of oxygen, and facultative cells can adapt to the presence or absence of oxygen.

What are the typical size and doubling time of prokaryotic cells?

Prokaryotic cells are typically $0.5 - 3\,\mu m$ in size and have a fast doubling time of approximately $20\,\text{minutes}$.

How do Gram-positive and Gram-negative bacteria differ in cell wall structure and Gram staining behavior?

Gram-positive bacteria have a thick peptidoglycan wall bonded with teichoic acids outside the cell membrane and retain the purple crystal violet stain. Gram-negative bacteria have an outer membrane containing lipopolysaccharides (LPS), a periplasmic space with a thin peptidoglycan layer, an inner membrane, and take on the color of the counterstain.

What are the functions of the rough and smooth endoplasmic reticulum (ER)?

The rough ER is covered with ribosomes and serves as a site for protein synthesis, whereas the smooth ER lacks ribosomes and synthesizes lipids.

How do prokaryotes and eukaryotes compare in genome organization and cell size?

Prokaryotes range from $0.5 - 3\,\mu m$ and possess a genome consisting of one DNA strand without a nuclear membrane. Eukaryotes range from $5 - 20\,\mu m$ and contain many DNA strands (chromosomes) enclosed within a defined nuclear membrane.

What cellular function does magnesium serve, and what industrial sources provide it in growth media?

Magnesium serves as an enzyme and chlorophyll cofactor and is present in some cell walls. Industrial sources include $MgSO_4 \cdot 7H_2O$ and $MgCl_2$.

What is the difference between defined media and complex media in industrial cell culture?

Defined media contains precise, known amounts of pure chemical components, making media higher cost but product recovery easier and cheaper. Complex media contains natural products (e.g., molasses, peptone), making media less expensive but product recovery and purification harder and more costly.

What percentage of a cell is water, and what element comprises 50% of a cell's dry weight?

Cells are $80\%$ water, and carbon makes up $50\%$ of their dry weight.

What are the structural compositions and primary functions of triacylglycerides, phospholipids, and sphingolipids?

Triacylglycerides consist of 3 fatty acids attached to glycerol and function in energy storage and insulation. Phospholipids consist of 2 fatty acids and a phosphate-containing group on glycerol and form cell membranes. Sphingolipids consist of 1 fatty acid attached to a sphingoid base and function in membrane formation and cell signaling.

How do saturated and unsaturated fatty acids differ in structure and impact on membrane fluidity?

Saturated fatty acids lack double bonds and are less fluid. Unsaturated fatty acids contain double bonds (usually cis) that introduce kinks into the carbon chain, disrupting tight packing and providing fluidity to cell membranes.

How do amphiphilic lipids assemble in water, and what determines permeability across a lipid bilayer?

In water, amphiphilic lipids assemble into a bilayer with hydrophobic fatty acid tails facing inside and hydrophilic polar heads facing water. Water and nonpolar molecules rapidly cross the bilayer, whereas polar and charged molecules cannot.

Which sterols are found in animal, plant, and yeast cell membranes?

Animal cell membranes contain cholesterol, plant cell membranes contain stigmasterol and $\beta\text{-sitosterol}$, and yeast cell membranes contain ergosterol.

What are the definitions and cellular functions of oligosaccharides versus polysaccharides?

Oligosaccharides are chains of fewer than 20 monosaccharides used for cell-cell recognition. Polysaccharides are chains of more than 20 monosaccharides used for energy storage (e.g., starch) or structural support (e.g., cellulose and chitin).

What sugar and nitrogenous base components differentiate DNA from RNA?

DNA contains deoxyribose sugar and the bases Adenine, Guanine, Cytosine, and Thymine. RNA contains ribose sugar and the bases Adenine, Guanine, Cytosine, and Uracil.

Which nucleotide bases are classified as purines and which as pyrimidines?

Purines are double-ring bases comprising Adenine and Guanine. Pyrimidines are single-ring bases comprising Cytosine, Thymine (in DNA), and Uracil (in RNA).

What complementary base pairing and hydrogen bonding rules exist in double-stranded DNA?

Adenine (A) pairs strictly with Thymine (T) via 2 hydrogen bonds, while Cytosine (C) pairs strictly with Guanine (G) via 3 hydrogen bonds.

What are the structural dimensions of the DNA double helix?

The DNA double helix is a right-handed structure with $10\text{ base pairs}$ per turn, a turn length of $3.4\,nm$, and a helix diameter of $2\,nm$.

Why is DNA replication described as semiconservative?

DNA replication is semiconservative because each newly formed double-stranded DNA duplex contains one original parental DNA strand and one newly synthesized complementary strand.

What are the primary functions of mRNA, rRNA, and tRNA?

Messenger RNA (mRNA) acts as a complementary transcript of DNA; Ribosomal RNA (rRNA) catalyzes protein synthesis in ribosomes; Transfer RNA (tRNA) carries specific amino acids to translate mRNA codons into proteins.

What structural features characterize transfer RNA (tRNA)?

tRNA has a cloverleaf shape featuring an amino acid attachment site at its $3'$ hydroxyl end and an anticodon composed of 3 nucleotides that base-pair to a complementary mRNA codon.

What is a codon, and why is the genetic code described as redundant?

A codon is a triplet sequence of 3 bases on mRNA that encodes a single amino acid or stop signal. The code is redundant because multiple distinct codons can code for the same amino acid.