Molecules of Life
What is the difference between an element and a molecule?
An element contains only one type of atom; a molecule is made of two or more atoms bonded together
What are three differences between prokaryotes and eukaryotes?
What are the base pairings in RNA and DNA?
In RNA: Adenine-Uracil, Guanine-Cytosine In DNA: Adenine-Thymine, Guanine-Cytosine
What cellular machines carry out translation?
Ribosomes
Describe the structure of amino acids that all have in common.
Alpha carbon (C), amino group (NH2), Carboxyl group (CO2H), H, R group
Which four major elements make up most of life?
Carbon, Oxygen, Hydrogen, and Nitrogen
Which organelles are part of the endomembrane system?
Nuclear envelope, rough and smooth endoplasmic reticulum, golgi apparatus, lysosome, vesicles, plasma membrane
Where do transcriptional activator proteins and general transcription factors attach?
Enhancer sequence; promoter sequence
What are the three ribosomal sites and what are their functions in translation?
A (tRNA entry), P (peptide bond formation), E (exit)
How are amino acids joined together? (bond and process)
Covalent peptide bonds; dehydration synthesis reaction
What functional group is circled here and is it polar or nonpolar?
Sulfhydryl
A scientist bleaches part of a cell membrane with a laser. Over time, the bleached spot regains fluorescence. What model does this experiment support, and why?
The fluid mosaic model; proteins and lipids move laterally in the membrane
Describe the structure of DNA in detail
Nucleotides w/ a phosphate group, deoxyribose sugar, and base; Sugar + phosphate backbone connected via phosphodiester bonds; antiparallel right-handed double helix; H bonds b/w bases on opp. strands; VDW forces b/w bases on same strand
Why is genetic code considered redundant but not ambiguous?
Multiple codons code for the same amino acid, but no codon codes for more than one amino acid
What are the differences between the two secondary structures of proteins?
Alpha Helix: right-handed helices, H bonds between Carbonyl group and amide group 4 amino acids ahead, very stable; Beta Sheet: parallel or antiparallel strands, H bonds between Carbonyl group and amide group on separate chains
Sodium (Na) transfers an electron to chlorine (Cl). What bond results, and why do salts like NaCl dissolve in water?
Ionic bond; water’s polarity allows hydrogen to interact with Cl⁻ and oxygen to interact with Na⁺
Compare facilitated diffusion, primary active transport, and secondary active transport in terms of energy use and direction of molecule movement.
Facilitated diffusion moves molecules high → low without energy; primary active transport uses ATP to move low → high; secondary active transport uses gradients established by primary active transport to move other molecules
A eukaryotic pre-mRNA must undergo three processing steps before leaving the nucleus. Name them and explain their purpose.
5′ cap (stability, ribosome recognition), poly(A) tail (stability, export), intron removal/splicing (produces functional coding sequence)
How does initiation of translation in eukaryotes vs. prokaryotes differ?
Eukaryotes: ribosome binds 5′ cap, scans for AUG codon; Prokaryotes: ribosome binds Shine-Dalgarno sequence internally
Which amino acid can form disulfide bridges?
Cysteine
Compare Van der Waals forces and hydrogen bonds in biological molecules. Which is weaker, and why are both critical to the structure of biomolecules like lipids and proteins?
Van der Waals forces are weaker (transient interactions between hydrocarbon chains), but they stabilize membranes; hydrogen bonds (partial charge attractions) stabilize protein secondary structure and DNA base pairing
Phospholipids are amphipathic. What does this mean and how does it lead to spontaneous formation of membranes in water? Plus, describe the membranes formed.
They have hydrophilic heads and hydrophobic tails; in water, they self-assemble into bilayers and liposomes (phospholipids with small head and 2 tails in donut shape) or micelles (phospholipids with large bulky head and 1 tail) with tails inside and heads outside
Why can one human gene lead to multiple different proteins? Give the mechanism and its evolutionary advantage
Alternative splicing produces different mRNAs by including/excluding exons; increases protein diversity without more genes
What are the three stages of translation, what do they do, and what triggers each transition?
Initiation begins at AUG/start codon (initiation complex forms); elongation proceeds as tRNAs add amino acids; termination occurs when stop codon is reached, release factor binds, and ribosome dissociates
Hydrophilic, polar