Chemical Basis of Heredity Review
1. What is a deoxyribonucleotide? DNA Nucleotide
Ribonucleotide? RNA Nucleotide
Name all of the subunits (sugars, bases, phosphate) in nucleotides.
Deoxyribose sugar/ribose sugar, phosphate group, adenine, thymine,
guanine, cytosine and uracil
2. What are purines? Double ringed nitrogenous bases which include adenine
and guanine
Pyrimidines? Single ringed nitrogenous bases which include thymine,
cytosine and uracil
3. What is the fundamental difference between the DNA of one organism and
another?
The relative amount of DNA present among varying species and the
order/sequence of the base pairs among organisms of the same species.
4. What base pairs exist in DNA? A-T with 2 H bonds, C-G with three H bonds
RNA? A-U with 2 bonds, C-G with 3 bonds
5. What is meant by the terms double helix, semi-conservative replication, antiparallel?
See notes all terms refer to the structure of the double helix of DNA
6. What is the difference between mRNA and DNA?
Deoxyribonucleic acid
AGCT
Ribonucleic acid
AGCU
Double stranded
Single stranded
DNA is larger/longer (entire genome)
RNA shorter (single gene)
Located only in nucleus
Found throughout the cell
Deoxyribose sugar
Ribose sugar
7. If one strand of DNA had the base sequence A A G C T T T C G A A T C T G,
what would the sequence on the complementary strand of DNA be?
AAG CTTTCGAATCTG
TT CGAAAGCTTAGAC
8. What kind of bond occurs between the bases of the complementary strands of
DNA? Hydrogen bonds A-T 2 bonds, G-C three bonds
9. What kind of bond occurs between the sugar and phosphate units on the DNA
backbone? Phosphodiester bonds
10. How is DNA replicated? Explain. Discuss the relevance of 3’ and 5’ ends.
See notes on Replication and animations. Include: Separation,
Complementary base pairing and joining, DNA polymerase only working in
the 5`-3`direction resulting in a leading and lagging strand made up of okazaki
fragments.
11. What is a template? A guide used for complementary base pairing.
12. Lagging strand? Strand of DNA synthesized discontinuously in the 5’-3’
direction resulting in okazaki fragments that must be joined together with DNA
ligase.
Leading strand? Strand of DNA synthesized continuously in the 5’-3’ direction.
13. What role do DNA polymerase and DNA ligase play in gene replication?
DNA polymerase adds DNA nucleotides to the 3’ end of the growing DNA
molecule. DNA ligase forms the phosphodiester bonds between the okazaki
fragments on the lagging strand.
14. What two bases can pair with adenine? T and U
15. How many strands of DNA serve as a template in transcription? One
16. What is the function of a ribosome?
To act as the site of protein synthesis where the mRNA, temporarily bonds so
that the codons can be read and the protein can be assembled.
17. What is tRNA and how does it differ from mRNA?
tRNA is a ~ 80 bp segment of RNA whose role is to bring the correct amino
acid to the ribosome for protein synthesis this is achieved by the anticodon on
the tRNA which is complementary to the codon on the mRNA molecule.
18. What is a cell’s source of supply of amino acids?
Amino acids are free in the cytoplasm many of them originate from protein in
our diet.
19. What is a codon?
A three letter word found on the mRNA which codes for a specific amino acid or
start/stop. It is complementary to the DNA sequence with the exception of T
replaced with U.
Anticodon?
A three letter word found on the tRNA which is complementary to the mRNA
codon.
20. What is the definition of a gene?
A segment of DNA that codes for a specific phenotype.
21. What happens to transfer RNA after it has dropped off its amino acid?
It recharges by finding another amino acid to replace the one it deposited in the
protein.
22. What happens to messenger RNA after it has been used to make a protein and
is detached from the ribosome?
It can attach to another ribosome and continue to make protein, or if no more
protein is required it is recycled into RNA nucleotides.
23. Describe the similarities and differences between mRNA, tRNA, and rRNA?
Types of RNA
mRNA
tRNA
rRNA
Characteristics and key functions
Found throughout the cell. Formed from the transcription of the DNA
molecule and carries the information required for protein synthesis.
Contains codons.
Found in the cytoplasm of the cell carries amino acids to the site of
protein synthesis. Contains an anticodon.
A structural component of the ribosome.
24. Write the order of nucleotides in mRNA that would be transcribed from the
following strand of DNA: G T A T A C C A G?
mRNA C A U A U G G U C
25. If the bases of messenger RNA read C A A A U G G U C, how many mistakes
were made during the transcription? One error or point mutation resulted.
Identify the amino acids that would form for question 21 His, Meth, val, and
for question 22. Gln, Meth, val
26. Describe Griffith’s experiment – what did it show? See notes.
27. What is an intron? Intervening non-coding portion of mRNA primary transcript
found only in eukaryotes which are removed during mRNA modifications. Exon
Coding portions of the mRNA primary transcript.
28. What takes place in post-transcriptional modifications?
Introns are removed, exons are joined back together by splicosomes, the
mRNA receives a 5’ Cap and a 3’ poly A tail
29. What are polypeptides? Another word for protein.
30. Where does translation occur? Cytoplasm
What are initiation, elongation, and termination? See notes on Protein synthesis
and checkout the animations available on my weebly.
31. What specific different kinds of mutations can occur in DNA?
Point mutations: Silent, missense and nonsense. Look up meanings of each.
Frameshift: Addition and deletion.
32. What is a mutagen? A mutagen is a substance that alters the sequence of the
DNA molecule or disrupts DNA replication in such way that errors are made.
Examples? UV radiation and radiation in general, drugs, chemicals.