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Running head: GENETICS 1

Genetics

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GENETICS 2

1. The process of DNA replication is linear and specific. Two distinct chemical

processes are involved, i.e. replication and transition. In replication,

deoxyribonucleotides are assembled linearly by a particular pairing of bases, forming

a replica of the original cellular structure. “This is followed by transcription, where

the genetic components produce messengers that transport protein-producing stations,

which is the information useful in defining the structure of the polypeptide chain”

(Rabeau, 2006). In this case, ribonucleotides are employed; while only one of the

DNA strands is employed in imitating into an RNA transcript. Replication of the cells

using N-15 achieves new replica, having the N-15 structure. Further, transition

process, where N-14 is used, only one of the original DNA strands are used, hence

resulting cells have N-15 and N-14 in the ratio 1:1.

2. a); b)

Percentage of bases based

on molarity

Organism

Adenine

Thymine

Guanine

Cytosine

(A+G)/(T+C)

(A+T)/(C+G)

Escherichia coli

23.9

24.9

25.2

1.04

1.00

Streptococcus pneumoniae

29.8

31.6

20.5

1.01

1.59

Yeast

31.7

32.6

18.3

17.4

1.00

1.80

Turtle red blood cells

28.7

27.9

21.3

1.03

1.31

Salmon sperm

29.7

29.1

20.8

20.4

1.02

1.43

Chicken red blood cells

28.4

21.6

1.00

1.29

Human liver cells

30.3

19.5

19.9

0.99

1.54

c) Some of the ratios happen to be constant in a but vary in b; “because the mobility

of the different molecules varies depending on certain conditions” (Randerath,

1964), hence a direct effect on the rate of replication.

GENETICS 3

3. There are more H2A histone molecules than H1 histone molecules in a chromatin

because “the H2A molecules have an active role in transcriptional silencing” (Filion,

2010). This means that they act as regulators to the process of cell multiplication

through transcription. I would not expect to find more H2A or more H3 histone

molecules in a chromatin; because these are involved in many detrimental processes,

e.g. ribosome formation, DNA repair, transcription activity among others. Thus, the

need for a regulated process for a functional cellular system.

4. DNA replication in a eukaryotic cell. “DNA replication process” (Jacob, 1963).

GENETICS 4

DNA Template

Lagging strand

Leading strand

5’

”’’

’’

3’

DNA Template

Okazaki fragment

Direction of fork movement

5’

”’’

’’

RNA primer

3’

5’

GENETICS 5

5. Definitions:

a. DNA helicase: this is the enzyme that is responsible for facilitation of DNA

replication, through unzipping of DNA strands to allow attachment and expose the

nucleotides used as templates in the process.

b. DNA polymerase I: a specially designed enzyme that helps in the process of DNA

replication, through removing the RNA primer and filling the nucleotides which

are necessary for the formation of DNA in the 5' to 3' direction. Furthermore, it

proof-reads, to ensure there are no mistakes in the replication while matching the

base pairs.

c. DNA polymerase III: this is an enzyme responsible for facilitating DNA

replication, mainly through accelerating the replication of the leading and lagging

strands.

d. DNA ligase: this is the enzyme responsible for joining nucleotides during DNA

replication, thus forming continuous DNA strands.

e. Primase: this is an enzyme that synthesizes RNA primers during DNA replication.

f. Topoisomerase: this refers to drugs that have an effect on the DNA replication

process, and are thus used in order to alter a DNA replication process. For

instance, during cell division, chromosomes separate from one another after

exchanging information through recombination. Thus, a chromosome can be

exchanged for DNA in a sister chromosome molecule, in order to alter genetic

information. This is made possible through topoisomerases.

g. Telomerase: these refer to the end regions of the DNA chromosomes, which

consist of telomeric repeat sequences. These ensure that there is the replication of

a complete version of each chromosome to avoid DNA damage or losses.

GENETICS 6

h. Single-strand binding proteins: this refers to a type of protein mainly found in

Escherichia Coli bacteria, that binds itself to regions of DNA that have only one

strand.

GENETICS 7

References

Filion, G. J., van Bemmel, J. G., Braunschweig, U., Talhout, W., Kind, J., Ward, L. D., ... &

van Steensel, B. (2010). Systematic protein location mapping reveals five principal

chromatin types in Drosophila cells. Cell, 143(2), 212-224.

Jacob, F., Brenner, S., & Cuzin, F. (1963, January). On the regulation of DNA replication in

bacteria. In Cold Spring Harbor Symposia on Quantitative Biology (Vol. 28, pp. 329-

348). Cold Spring Harbor Laboratory Press.

Rabeau, J. R., Reichart, P., Tamanyan, G., Jamieson, D. N., Prawer, S., Jelezko, F., ... &

Wrachtrup, J. (2006). Implantation of labeled single nitrogen-vacancy centers in

diamond using N 15. Applied Physics Letters, 88(2), 023113.

Randerath, K., & Randerath, E. (1964). Ion-exchange chromatography of nucleotides on

poly-(ethyleneimine)-cellulose thin layers. Journal of Chromatography A, 16, 111-

125.

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