Chapter 14 - DNA structute And Function Flashcards
What is the definition of a gene
A sequence of DNA that codes for a functional protein
The human genome contains between how many functional genes?
21-25 thousand
What did Erwin chargaff discover about the amount of the nucleotides?
Adenine equaled thymine and cytosine equaled guanine, ect
What is the chargaffs rule?
Adenine = thymine and guanine = cytosine
What are the monomers that build DNA?
Nucleotides
What is central in the nucleotide structure?
A 5 carbon sugar (Pentose)
What is at the 1’ position on the nucleotide?
One of the five possible nitrogenous basses is attached to
What is at the 2’ position on the nucleotide?
A -OH group attached for DNA, and a -H for RNA
What is at the 3’ position for nucleotides?
A -OH group that forms a phosphodiester bond with the phosphate group of the adjacent nucleotide
At the 5’ end of the nucleotide what is attached?
The phosphate group
What is a nucleotide made up of all together?
A Pentose sugar, a nitrogenous base, and a phosphate group
What are the 2 overall groups of the nitrogenous basses and what are their structures? What nitrogenous bases are present in each group?
Purines (double ringed structures)
- Adenine
- Guanine
Pyrimidines (single ringed structure)
-Cytosine
-thymine(DNA ONLY)
-Uracil(RNA ONLY)
Do purines pair with pyramidines, or purines with purines and pyramidines with pyramidines
Purines with pyramidines
What does the chargaffs rule state are the pairings for DNA and RNA?
DNA:
Adenine = Thymine
Guanine = Cytosine
RNA:
Adenine = Uracil
Cytosine = Guanine
How are base pairs formed? Chemically?
Nitrogenous basses extend from the 1’ carbon of the Pentose sugar and hydrogen bond with another nucleotide
Nucleotides combine with each other through what bond? And where chemically?
Phosphodiester bonds, 1 water linkage with the 5’ carbon of one nucleotide and another ester linkage with the hydroxyl group of the 3’ carbon of the next nucleotide
Who determined the structure of DNA?
James Watson and Francis Crick
It was determined that the DNA molecule was composed of what chemically on the inside of the backbone sugar?
2 strands of nucleotides held together by hydrogen bonds between the nitrogenous basses of the nucleotides thus taking the form of a double helix
In the ends of the 2 nitrogenous basses are what molecule?
The sugar-phosphate backbone
How many hydrogen bonds are in between A and T vs C and G?
A and T has 2 hydrogen bonds while C and G has 3
What are larger pyramidines or purines?
Purines are larger than the pyramidines
What does each end of the sugar phosphate backbone always end with?
A phosphate attached to the 5’ carbon of the sugar, and the opposite end of the same sugar-phosphate backbone therefore must end at the -OH of the 3’ end
What charge does DNA have?
Negative
How does the bands appear in gel electrophoresis?
As the DNA moves through the gel the smaller fragments move through the gel faster and appear as bands
Larger amounts of DNA have denser bands
Why are stains used to visualize the bands?
Because they are sensitive to UV light
Where is prokaryotic DNA found? In what form?
A single circular chromosome which is found in the nucleoid region of the cell?
When are chromosomes at their most compact stage in eukaryotes?
Metaphase
Interphase eukaryotic chromosomes contain what 2 distinct regions? Describe each one
Heterochromatin - is tightly compact and does not contain expressed genes and is found around the centromeres and telomeres (ends of the chromosome)
Euchromatin - contains genes that are transcribed (copied and sent to the ribosome for translation of proteins) with DNA that are not further compacted than regular nucleosomes
When are the 2 strands of the double helix seperated? And how come?
In the copying process since the hydrogen bonds are weak, and each strand can act as a template from which a new complementary strand can be copied
After the copying of a new double helix what is each strand made of?
One strand is the old strand and the other is the new strand