DNA - the molecule of heredity

Assignment

Audesirk, Audesirk & Byers Chapter 9, part of Chapter 10 and several figures from other chapters

Today's musical selection
Waltz round the cycle

History

Figure 9-1
It was not until the 1940's that it was proved that DNA was the material of heredity.
(work of Griffith and Avery) S (smooth) bacteria kill mouse, R (rough) not, DNA from S can transform R to make them deadly.

Central dogma

Figure 10-3
One "gene" codes for one "protein"
Central Dogma (of cell biology)
DNA (nucleus, virus) ONE GENE
->transcription->
mRNA (nucleus to cytoplasm in eukaryotic cell)
->translation->
Protein ONE PROTEIN

Figure E19-2a
retrovirus, like HIV, makes DNA from a template of RNA using an enzyme called reverse transcriptase.

Figure 10-2
RNA's: m (messenger), r (ribosomes), t (transfers aa's)

Table 10-1
Nucleic acids: nucleotide = sugar, PO4 & base (no essential nucleic acids)
Sugar (ribose or deoxyribose), phosphate (PO4), base
4 bases in DNA: Adenine, Guanine, Thymine, Cytosine
4 bases in RNA: The same except Uracil instead of Thymine
purines - A & G, pyrimidines - C, T, U

How can DNA lead to so much biological variability?

Two in a row nucleotides in a row would give 4 x 4 = 16 possibilities.
This is < 20, the number of amino acids, so 2 would not be enough for code.
It takes a longer macromolecule of DNA to code for a protein than the protein it codes for.

Table 10-3
(The genetic code)
4 x 4 x 4 - there is a 3 letter word (codon) consisting of 4 letters for each amino acid.
However 4 x 4 x 4 = 64 is more than enough (redundant) and the word for this is degeneracy, in that there are several codes for certain of the amino acids.

DNA has a built in way to reproduce itself accurately...

Figure 9-6
DNA is a double helix, with A across from T and C across from G
this pairing is essential for DNA to reproduce itself.
DNA is quite stable and accurate in its replication.

...and to orchestrate transcription and translation

Figure 10-9
In making RNA, the same pairing applies except that U is across from A.

More detail on DNA replication

Figure E9-7
each strand contains all the information necessary, put into action by each strand being capable of organizing the other strand; but instead of the two strands separating entirely and generating the daughter strand, numerous bubbles form where the parental strand is copied at the replication fork.

5'->3' direction replication fork
enzymes:
DNA helicase and leading strand DNA polymerase
lagging strand:
DNA polymerase makes one piece at a time
DNA ligase puts pieces together

Mutations

Figure 12-29
Sickle-cell anemia

Figure 9-8
DNA is quite stable and accurate in its replication. However, sometimes factors such as chemical mutagens and ionizing radiation cause alterations called mutations. In the fully evolved organism, mutations are usually deliterious, but they can sometimes create an advantage. On the evolutionary time scale, mutations have been the driving force of divergent evolution and adaptive radiation.

Disorder which turns human red blood cells (erythrocytes) sickle shaped (sickle cell anemia) is caused by a mutation substituting Val for Glu at amino acid #6 in the beta chain of hemoglobin. This disorder is high in African-American of equatorial African origin. Homozygous, it is very bad, but heterozygous, it confers resistance to malaria.

Orientation for using microscopes in cell lab (and other labs)

Fig. 1 - Start with the lowest power objective with the stage all the way up
Fig. 2 - Best to use your left hand on the focus knobs...
Fig. 3 - ...so that your right hand is available to move the slide

To find and focus your specimen:
(1) put a landmark, like the edge of the cover slip or a highly stained part of the slide in the light beam
(2) [from the stage up position with the lowest power objective, see above] move the slide's landmark back and forth (right hand) (or up and down) continuously while moving the stage down (left hand)
(3) when the landmark is in focus, find the specimen
(4) the microscope is parfocal, meaning that you can then go to higher power objectives and be reasonably close to focus

Questions used in 2007 and 2008 relating to this outline

In the genetic code, how many different triplets are there?
(a) 3
(b) 4
(c) 16
(d) 20
*(e) 64

What substance from S bacteria convert R bacteria into a form that is lethal to mice?
*(a) DNA
(b) NADH
(c) Glycogen
(d) ATP
(e) Protein

In transcription,
(a) mRNA is used to make protein.
(b) the ribosomes are used.
*(c) DNA is used to make mRNA.
(d) the anticodon is matched to the codon.
(e) RNA is used to make DNA.

HIV (human immunodeficiency virus)
(a) remains outside the cell like a bacteriophage.
(b) is made up of DNA and protein.
(c) is the only virus (or organism) with degeneracy in its genetic code.
(d) works backwards by using anticodons instead of codons.
*(e) uses reverse transcriptase.

How might a complementary vs. a template DNA strand differ?
(a) Across from U would be A.
*(b) Across from A would be T.
(c) Across from C would be C.
(d) Across from G would be glycine.
(e) Across from DNA would be RNA.

Replication forks would be used in conjunction with
*(a) DNA polymerase.
(b) translation.
(c) reverse transcriptase.
(d) sickle cells.
(e) heterozygous mutations.

A ribosome is used to assist in the process of
(a) transcription.
(b) copying DNA into mRNA.
*(c) translation.
(d) conversion of ATP to ADP.
(e) dehydration synthesis.

Transfer RNA (tRNA) is used in the process of
(a) oxidative phosphorylation.
(b) exocytosis.
(c) producing a karyotype.
(d) crossing over.
*(e) translation.

Which is NOT true about HIV (Human Immunodeficiency Virus)?
(a) It goes into the cell it infects.
*(b) It belongs to the kingdom of protista.
(c) Causing AIDS, it preferentially depletes helper T cells.
(d) Its hereditary material is RNA.
(e) Reverse transcriptase is already present.

A ribosome is used to assist in the process of
(a) transcription.
(b) copying DNA into mRNA.
*(c) translation.
(d) conversion of ATP to ADP.
(e) dehydration synthesis.

Transfer RNA (tRNA) is used in the process of
(a) oxidative phosphorylation.
(b) exocytosis.
(c) producing a karyotype.
(d) crossing over.
*(e) translation.

Which is NOT true about HIV (Human Immunodeficiency Virus)?
(a) It goes into the cell it infects.
*(b) It belongs to the kingdom of protista.
(c) Causing AIDS, it preferentially depletes helper T cells.
(d) Its hereditary material is RNA.
(e) Reverse transcriptase is already present.

Because of degeneracy of the DNA code,
A) the HIV retrovirus disobeys central dogma.
B) most mutations are bad.
C) both strands can be used for DNA to reproduce itself, but only one strand can be used to code for a specific protein.
D) it takes four nucleotides in a row to determine one amino acid.
*E) it might be possible to have a mutation in the DNA without changing the protein it codes for.

Which is NOT true about hemoglobin?
A) It contains iron.
B) It is in red blood cells.
C) It is altered in sickle cell anemia.
*D) It is an enzyme that makes DNA from a template of mRNA.
E) It is a protein used for the transport of oxygen.

Which would have the greatest potential for variability?
*A) a peptide 3 amino acids long
B) a nucleotide chain 3 base pairs long
C) a hydrocarbon 3 carbons long
D) a glycogen chain 3 glucose molecules long
E) ATP

What was the main point of Griffith's experiments with pneumonia in mice?
A) A mutation is how the R strain becomes the S strain.
B) DNA was reverse transcribed into RNA using DNA ligase.
C) Protein carries the code for heredity.
D) RNA is translated into DNA.
*E) There is a substance present in dead bacteria that can cause a heritable change in living bacteria.

DNA has
A) A, U, G, and C bases.
B) only purines.
C) anticodons.
*D) C, T, A, and G bases.
E) all 5 bases: A, U, G, T, and C.

The DNA of a certain organism has guanine as 30% of its bases. What percentage of its bases would be adenine?
A) 0%
B) 10%
*C) 20%
D) 30%
E) 40%

For the DNA sequence GCCTAT in the template DNA strand, the sequence found in the complementary DNA strand is
*A) CGGATA.
B) GCCATA.
C) CGGAUA.
D) ATTCGC.
E) GCCTAT.

How does the Watson and Crick model of DNA structure help explain DNA replication?
A) Uracil is always across from Thymine.
*B) Precise base pairing allows the base sequence to be copied.
C) Methionine is the amino acid for the stop codon.
D) Some amino acids are purines and these are mutated to different amino acids, pyrimidines.
E) It doesn't; DNA never replicates.

A stretch of DNA 10 nucleotides long can have how many possible sequences of the four bases?
A) one
B) four
C) ten
D) hundreds
*E) way more than any of the above

Questions used in 2002 relating to this outline (and other outlines)

Which would have the greatest potential for variability?
(a) a nucleotide 3 base pairs long
*(b) a peptide 3 amino acids long
(c) a hydrocarbon 3 carbons long
(d) a glycogen chain 3 glucose molecules long
(e) ATP

Which nucleotide base is used in RNA but not DNA?
(a) cytosine
(b) adenine
(c) thymine
*(d) uracil
(e) guanine

Ribosomes might be situated (A-where?) and serve (B-what function?).
(a) A in the nucleus; B to store genetic information.
(b) A in the Golgi apparatus; B to deliver energy.
*(c) A in the rough endoplasmic reticulum; B to synthesize proteins.
(d) A in the plasmalemma; B to mediate transcription.
(e) A in the desmosome; B to carry the genetic code for each protein.

Making mRNA from a template of DNA is called
(a) respiration.
(b) glycolysis.
(c) motility.
*(d) transcription.
(e) fluorescence.

Because of degeneracy of the DNA code,
(a) the HIV retrovirus disobeys central dogma.
(b) most mutations are bad.
(c) both strands can be used for DNA to reproduce itself, but only one strand can be used to code for a specific protein.
(d) it takes four nucleotides in a row to determine one amino acid.
*(e) it might be possible to have a mutation in the DNA without changing the protein it codes.

Which is a purine base of a nucleotide?
*(a) adenine
(b) ribose
(c) phenylalanine
(d) lactic acid
(e) actin

Which is not true about hemoglobin?
(a) It contains iron.
(b) It is in red blood cells.
(c) It is altered in sickle cell anemia.
*(d) It is an enzyme that makes DNA from a template of mRNA.
(e) It is a protein used for the transport of oxygen.

A ligase would be used in
(a) control of gene transcription.
(b) synthesis of DNA from the hereditary molecule in the HIV (human immunodeficiency virus).
(c) western blotting.
*(d) lagging strand replication.
(e) cutting open a plasmid to prepare for cloning a gene.

In the 1940's, Avery and others showed DNA was the important part of smooth bacterial extract that made rough bacteria pathogenic in Griffith's experiment. The phenomenon Griffith demonstrated is called
*(a) transformation.
(b) conjugation.
(c) cloning.
(d) hybridization.
(e) operon regulation.


Return to Bio 110 Syllabus

Return to Stark Home Page

This page was last revised 6/26/09