Transcription
Name the enzyme responsible for building an RNA molecule during transcription. Then describe what this enzyme does.
RNA polymerase. It uses the DNA template strand to build a complementary RNA molecule.
Name the cellular structure responsible for reading mRNA and using that information to build a polypeptide.
The ribosome, or rRNA
Describe the difference between a monosaccharide, disaccharide, and polysaccharide, and give one example of each.
Monosaccharide: one sugar unit; glucose
Disaccharide: two sugar units; sucrose
Polysaccharide: many sugar units; starch, glycogen, cellulose, or chitin
Describe the basic structure of lipids.
Carbon carbon and carbon hydrogen bonds, non-polar, unsaturated or saturated.
What are the four shared cell structures between eukaryotes and prokaryotes?
Cell membrane, genetic material, ribosomes, cytoskeletal elements
A double-stranded DNA molecule contains the following strands:
Coding: 5′–ATG CCG TAA–3′
Template: 3′–TAC GGC ATT–5′
Which strand does mRNA polymerase use to synthesize its strand? Which strand has the same sequence as the mRNA, except for T/U differences?
mRNA uses the template strand. The coding strand has the same sequence as the mRNA, except DNA contains T and RNA contains U.
Name the three tRNA-binding sites on a ribosome and describe the general function of each.
A site: charged tRNA enters
P site: tRNA holding the growing polypeptide, peptide bond forms
E site: exit site for the uncharged tRNA
Two monosaccharides are joined together to form a larger carbohydrate. What type of bond connects them?
A glycosidic bond is formed
A fatty acid contains three carbon-carbon double bonds. Is it saturated or unsaturated? Explain
Unsaturated, because it contains one or more C=C double bonds.
Bacteria, archaea, eukarya
State the direction RNA polymerase moves along the template strand and the direction in which RNA is synthesized.
RNA polymerase moves 3′ → 5′ along the template strand. Another way to say this is that it moves downstream. RNA is synthesized 5′ → 3′.
Consider the following mRNA:
5′–CCG–AUG–UUU–GGC–ACU–UAA–GGG–3′
Starting at the correct location, determine the amino acid sequence produced. Identify the start and stop codons.
Translation begins at AUG
Met–Phe–Gly–Thr
Translation ends at UAA
Draw the difference between a polysaccharide with alpha-glycosidic linkages and beta-glycosidic linkages.
Alpha should look highly branched, beta should look structured. Beta has hydrogen bonds between the linear linkages.
Describe the two major regions of a phospholipid and explain how each region interacts with water.
The phosphate-containing head is hydrophilic and interacts with water. The fatty acid tails are hydrophobic and avoid water. Also can be called hydrophilic head and hydrophobic tail.
Explain the difference between the nucleus of a typical eukaryotic cell and prokaryotic cell.
Eukaryotic cells have membrane-bound nucleus containing chromosomes, prokaryotes can have linear chromosomes or singular, circular chromosomes.
The following DNA strand is the template strand:
3′–TAC GGA CTT ACG ATT–5′
Write the RNA molecule produced during transcription. Label the 5′ and 3′ ends.
5′–AUG CCU GAA UGC UAA–3′
A normal mRNA contains:
5′–AUG–GCU–AAA–UGG–UAA–3′
A mutation changes the codon UGG → UGA.
Predict what happens to the protein and explain your reasoning.
UGG normally codes for tryptophan, while UGA is a stop codon. Translation will therefore terminate prematurely, producing a shorter/truncated protein that may not function normally.
Explain how the structure of glycogen allows it to function as an energy-storage molecule.
Glycogen is highly branched, providing many ends where enzymes can remove glucose. There are also less hydrogen bonds, making it easier to break the bonds. This allows glucose to be mobilized relatively quickly.
Imagine placing thousands of phospholipids into water. Predict what will happen and explain why.
The phospholipids will spontaneously arrange into a bilayer, creating a vessicle. Hydrophilic heads face the water, while hydrophobic tails cluster away from water.
Compare microtubules, actin filaments, and intermediate filaments in terms of structure and function.
Microtubules → tubulin; transport tracks, chromosome movement, cilia/flagella
Actin → actin; cell movement, shape, contraction, cytokinesis
Intermediate filaments → mechanical strength and structural stability
A mutation occurs in a promoter region of a gene. Predict what could happen to transcription and explain why.
RNA polymerase may have difficulty recognizing or binding the promoter. As a result, transcription could decrease or fail to occur, leading to less or no mRNA and potentially less or no protein.
A tRNA carrying an amino acid is currently in the A site of the ribosome, while a tRNA carrying the growing polypeptide is in the P site.
What are the next major events in translation?
A peptide bond forms between the amino acids, transferring the growing polypeptide to the tRNA in the A site. The ribosome then moves along the mRNA, shifting the tRNAs through the ribosome so the empty tRNA can exit through the E site and the next tRNA can enter the A site.
Explain how differences in the structures of cellulose, chitin, glycogen, and starch allow each molecule to perform its biological function.
Cellulose → structural support in plants; strong fibers
Chitin → structural support in fungi/arthropods
Glycogen → highly branched animal glucose storage
Starch → plant glucose storage; structure allows energy storage/mobilization
You are given a structural model of an unfamiliar lipid. It contains four fused carbon rings and a small number of oxygen-containing groups.
Identify the lipid category and identify one specific type of this.
It is a steroid. It could be a cholesterol.
What makes something an organelle, and why is a ribosome not an organelle?
It is a specialized structure inside the cell and is membrane-bound. The ribosome does not fit this definition because it is not surrounded by a membrane.