Chapter 03: Cellular Structure, Proteins, and Metabolic Pathways

Practice flashcards covering cellular structure, membrane junctions, protein synthesis, binding sites, enzymes, and metabolic pathways from Chapter 03.

How are phospholipids arranged in the plasma membrane?

They form a double layer (bilayer) with nonpolar fatty acid tails in the center and polar heads facing the water inside and outside the cell.

How does cholesterol affect plasma membrane fluidity?

It sits between fatty acid tails to keep them from packing too closely, maintaining a balanced membrane fluidity.

What does the "fluid-mosaic" model describe?

It describes how membrane proteins can float and move within the lipid bilayer.

What is the function of integrins in cell membranes?

Integrins are proteins that link a cell to the extracellular matrix and connect it to neighboring cells.

What are the main structural features of desmosomes?

They are disk-shaped junctions separated by about $20\,\text{nm}$ that use dense plaques and cadherin proteins to hold stretching cells together.

How do tight junctions differ from desmosomes?

Tight junctions form a continuous band around cells like a zipper to block fluid leaks, whereas desmosomes are disk-shaped spots that withstand pulling forces.

What forms gap junctions, and what can pass through them?

Connexin proteins form small channels ($1.5\,\text{nm}$ wide) that allow small ions like $\text{Na}^+$ and $\text{K}^+$ to pass while blocking large proteins.

What is the main function of the cell nucleus?

To store DNA and pass genetic information to new cells.

What is the difference between chromatin and chromosomes?

Chromatin is loose, unwound DNA in non-dividing cells, while chromosomes are tightly packed, rod-shaped DNA structures formed during cell division.

What structure forms when DNA wraps around histone proteins?

Nucleosomes.

How are the $64$ DNA triplets divided by function?

$61$ triplets code for amino acids, and $3$ serve as stop signals to end protein synthesis.

What is the role of RNA Polymerase in transcription?

It binds to a gene's promoter region, unwinds the DNA, and builds an mRNA strand.

What is the difference between exons and introns?

Exons are coding sections that are expressed, while introns are non-coding sections that spliceosomes cut out of the mRNA.

What are the three main stages of translation?

Initiation (starting), Elongation (adding amino acids), and Termination (ending).

How do allosteric and covalent modulation differ?

Allosteric modulation involves weak, non-covalent binding at a regulatory site, while covalent modulation involves forming strong chemical bonds (like adding a phosphate group).

What is a signal sequence on a new protein?

A segment of the first $15$ to $30$ amino acids that tags a protein to be secreted or built into the cell membrane.

How are proteins broken down in a proteasome?

A peptide tag called ubiquitin attaches to the protein, directing it to a proteasome to be unfolded and chopped into small pieces.

What determines the chemical specificity of a protein binding site?

How well the shape and chemical properties of the binding site match a specific ligand.

What two factors determine the percent saturation of a protein binding site?

1. The concentration of unbound ligand in solution
2. The affinity (attraction) of the binding site for the ligand

Which enzymes add and remove phosphate groups on proteins?

Protein kinase adds phosphate groups (phosphorylation), and phosphoprotein phosphatase removes them.

How do cofactors and coenzymes differ?

Cofactors are metal ions that alter an enzyme's shape, while coenzymes are vitamin-based organic molecules (like $\text{NAD}^+$) that participate directly as substrates.

What three metabolic pathways produce ATP from food?

1. Glycolysis (in cytoplasm, anaerobic)
2. Citric Acid Cycle (in mitochondria, aerobic)
3. Oxidative Phosphorylation (in mitochondria, aerobic)

Which amino acids are essential?

Histidine, Isoleucine, Leucine, Lysine, Methionine, Phenylalanine, Threonine, Tryptophan, and Valine.

Which vitamins are fat-soluble?

Vitamins A, D, E, and K.