Genetics Mini Exam I: The Structure of DNA
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DNA is the genetic material with the two functions of __ and __
acting as units of biological information as well as units of inheritance
Structure of DNA
- long and chainlike
- made of monomers called nucleotides, which form polynucleotides
The basic unit of the DNA molecule is the __, which is found in the cell either as __ or __
- components of nucleic acids or as individual molecules
c. Structure of the nucleotide:
i. Sugar: a pentose called 2’-deoxyribose
nitrogenous base: attached to the 1’ carbon
Explain the sugar in more detail:
- how do they exist?
- what is replaced?
- 1. Pentoses can exist as straight chains (Fischer) or rings (Haworth)
- 2. The 2’ means that the hydroxide has been replaced with a hydrogen group
- a. Numbering sugars is important to indicate the position of other components
- purines: Adenine and guanine pyrimidines: thymine and cytosine
- the base is attached to the sugar by a beta-N-glycosidic bond attached to nitrogen number 1 of the pyrimidine or number 9 of the purine
What is a nucleoside?
a molecule comprising the sugar joined to a base
What is a nucleotide?
the attachment of a phosphate group to the 5' carbon of the sugar
up to three individual phosphates can be attached in series; they are alpha, beta, and gamma
How are polynucleotides formed?
by linking nucleotides together through phosphate groups (the alpha groups_
During polymerization, what happens?
The beta and gamma phosphates are cleaved off; the --OH of the carbon is cleaved off as well
The double helix exists in several different forms. Why?
The double helix that was studied by Watson and Crick is the B-form of DNA Other orientations can be formed by changing rotation around the Beta-N-glycosidic bond, which has a significant effect on the double helix, as it alters the relative positioning of the two polynucleotides The relative positions of the carbons in the sugar can also be changed slightly, affecting the conformation of the sugar-phosphate backbone
B form vs. A form in terms of structure
B: 10 base pairs per turn of the helix with 0.34 nm between adjacent base pairs and a pitch of 3.40 nm A: 11 bp per turn, 0.29 nm between each two base pairs
Biggest difference between B and A
: A-DNA has a deeper major groove and a broader an shallower minor groove Proteins bind to DNA in this groove With A- DNA, it is easier because the bases are more exposed in the minor groove
The helix is left handed Sugar-phosphate adopts an irregular zigzag conformation More tightly wound, with 12 bp per turn and a diameter of 1.84
DNA is able to act as a store of biological information because of its __ and because there are __. The biological information contained in genes is written in __, which we call the __. The language is read through the process called __
- polymeric structure
- four different nucleotides
- genetic code
- gene expression
The average length of a gene is __, with __sequences.
In order to act as units of inheritance, genes must be able to __
Genes must also __, so that each of the two daughter cells can be given a complete copy of the biological information possessed by the parent cell.
- 1000 nucleotides
- be replicated every time a cell divides
If two polynucleotides in a DNA molecule are separated, then what happens and why?
two perfect copies of the parent double helix can be made simply by using the sequences of these preexisting strands to dictate the sequences of the new strands
Replication is performed by __, which build up a new polynucleotide by __, using the __ to ID which of the four nucleotides should be added at each position.
This is called __; and, it ensures that the double helix that is made is a __ from which the original polynucleotide was obtained.
- DNA polymerases
- adding nucleotides one by one to the 3’ end of the growing strand
- base-pairing rules
- template-dependent DNA synthesis
- precise copy of the double helix
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