Download DNA RNA Protein Hwk KEY

IB Biology Year 1
Name: __________________________________________ Per. _____
DNA, RNA, Protein Practice KEY
Directions: respond to these questions in the spaces provided.
1.
How do the data in the table at the right demonstrate
Chargaff's rules?
The % A is always about the same as % T, and the % G is
always about the same as % C. Watson & Crick thought
Chargaff's data suggested a base-pairing model of DNA.
2.
In DNA replication, what is the biochemical basis for the difference in how the leading strand of DNA is
synthesized relative to the lagging strand?
DNA (and RNA) synthesis can only proceed in the 5' to 3' direction. Enzymes are notoriously "finicky." Since
the leading and lagging strands are antiparallel, the polymerases can only synthesize directly the 5' to 3'
strand (leading); the lagging strand is synthesized 5' to 3' in small segments starting where the replication
fork was "unzipped."
3.
Lysine and arginine make up more than 20% of histone proteins' amino acids. Given the structure of DNA, why
is this expected? Hint: see the amino acid chart in Chapter 5 -- figure 5.16.
Lysine and arginine both have R groups with a positive charge (+). This would enable histones to bind well
with the sugar phosphate backbones of DNA, which carries negative charges (-).
4.
In Chapter 17, figure 17.4, compare the sequence of the messenger RNA (in red) to that of the nontemplate DNA
strand (reading from the 5' to 3' direction). What do you notice?
They are identical, except for RNA having a "U" where DNA has a "T." This shouldn't surprise us, since we
know that mRNA is a copy of a gene! Because DNA is double-stranded, mRNA is a copy of the nontemplate!
5.
Come up with your own metaphor for tRNA and explain how it works. Many possible answers!
6.
Make a T-chart to compare and contrast codons with anticodons: structural and/or functional, and significant.
CODONS
ANTICODONS
Part of which nucleic acid?
messenger RNA
transfer RNA
Where synthesized?
In nucleus
In nucleus
Size?
3 nucleotides
3 nucleotides
Temporarily binds to
tRNA anticodons
mRNA codons
Arrangement in cytoplasm? As part of a long chain Separate entities buzzing around
7.
Which of the following is not directly involved in translation? After circling the one not involved, write a brief
description of the roles of each of the 4 entities that are directly involved in translation.
DNA
GTP (like ATP) Provides energy to charge tRNA's, catalyze peptide bonding, and move ribosomes…
mRNA Its sequence of codons determines order of a.a.'s in protein
ribosome Holds mRNA; takes in tRNA-a.a.'s; rbs enzymes make peptide bonds between a.a.'s
tRNA Adapter molecules that carry a.a.'s to the rbs; their anticodons base pair with mRNA codons
8. … A scientist uses biotech methods to insert a human gene into bacterial cells, hoping the cells will express it
and synthesize functional human protein. Instead, the protein produced is found to contain many fewer amino
acids and doesn't work. What could have gone wrong? Perhaps the human gene contained one or more
introns. Prokaryotes like bacteria do not have introns in their genes and do not have cutting & splicing
enzymes. Perhaps the bacterial cells transcribed and translated the entire human gene, but the
bacterial ribosomes ventured into an intron and encountered a stop codon (like UGA). This would
result in a shorter protein, and of course structure influences function, so the short protein didn't work.