DNA Structure
What is the monomer of nucleic acids?
Nucleotides
According to Chargaff’s rules, if a DNA molecule contains 30% adenine (A), what percentage of its bases must be thymine (T)?
30% T
True or False: Transcription is the synthesis of a polypeptide (protein) which occurs from an mRNA template.
False
- Transcription is the synthesis of RNA from a DNA template.
- Translation is the synthesis of a polypeptide (protein) which occurs from an mRNA template.
What are the 4 components of an amino acid?
- Alpha (central) Carbon bonded to H
- Carboxyl group (COOH)
- Amino group (NH2)
- Variable R group (functional)
What is the difference between genotype and phenotype?
Genotype: Information carried in sequence of bases. The physical genes and organism possesses.
Phenotype: The consequence of the proteins that are expressed. Essentially, the traits we see expressed.
What kind of bonds are involved in DNA structure?
- Covalent phosphodiester bonds (backbone)
- Hydrogen bonds (between bases)
- Bonus: Technically, all molecules exhibit Van der Waals.
A DNA molecule is 40% guanine (G). What percentage of the molecule is made up of cytosine (C), adenine (A), and thymine (T) combined?
60%
(Because G = C, C = 40%, leaving 20% A + 20% T.)
Where do transcription and translation occur in the cell?
- How does it differ in eukaryotes vs. prokaryotes?
Transcription: Nucleus (eukaryotes), cytoplasm (prokaryotes)
Translation: Cytoplasm (prokaryotes & eukaryotes)
Describe the 4 levels of protein structure (primary, secondary, tertiary, quaternary)
Primary: Sequence of Amino Acids
Secondary: Alpha helix and beta sheets
Tertiary: Final folded shape of the protein (typically results in a functional form)
Quaternary: Multiple structures put together that function as one unit
______ --> ______ --> ________
(looking for 6 words, 1 for each blank, 1 for each arrow)
DNA --(transcription)--> RNA --(translation)--> Protein
Purine (double ringed): AG
Pyrimidine (single ringed): CUT
Write the complementary DNA strand for:
5′–ATGCCGTA–3′
3′–TACGGCAT–5′
Which main enzyme carries out transcription?
RNA polymerase
What kind of bonds link polypeptides?
Peptide bonds are covalent bonds that join two adjacent amino acids. This occurs through a dehydration synthesis reaction (water is removed, joining monomers).
True or False: DNA is double stranded, parallel, and complementary?
False
- DNA is double stranded, anti-parallel, and complementary.
Draw the Structure of a DNA Nucleotide
(Phosphate group bonded to 5', 3' OH, 2' H, 1' nitrogenous base)
A DNA sample contains 18% adenine. What are the percentages of T, G, and C?
A = 18%
T = 18%
G = 32%
C = 32%
What are the 3 main phases of transcription?
- Initiation
- Elongation
- Termination
What are the 3 main types of RNA used in translation?
1) mRNA (produced by transcription)
2) tRNA (adapter molecule in translation)
3) rRNA (used to make ribosomes)
What is a histone?
Small basic proteins that make up the nucleosome (octamer of 8 histones) around which DNA is wound.
- Organizes DNA
- Compacts DNA
- Regulates gene expression
How many hydrogen bonds are between
- G and C nitrogenous bases
- A and T nitrogenous bases
- G/C: 3
- A/T: 2
Write the complementary RNA sequence produced from this DNA template strand: 3′–TACGGAATC–5′
5′–AUGCCUUAG–3′
What is the promoter?
During transcription initiation, the region at which many accessory proteins (proteins necessary for transcription) bind (to form the transcription initiation complex). Specific sequence to which RNA polymerase binds to start transcription.
- In eukaryotes: TATA box (TATA sequence)
Describe the 3 special amino acids
1) Glycine (small, nonpolar --> Flexibility)
2) Proline (cyclic --> restricts protein folding)
3) Cysteine (forms disulfide bridges)
What is a codon?
A codon is a set of 3 nucleotides in the mRNA transcript that specifies 1 amino acid.