DNA Chapter 7.2 Flashcards
the 2 types of nucleic acids
dna ( deoxyribonucleic acid)
Rna ( ribonucleic acid)
Nucleotides
the building blocks of nucleic acid
structure of a nucleotide
sugar ( deoxyribose or ribose)
a phosphate group
nitrogenous base
They always have the the same sugars and phosphate but have one of the different nitrogenous bases.
DNA double helix resembles a twisted ladder or staircase
Railings —–( sugar phosphate backbone)
Alternating units of
deoxyribose and phosphate joined with covalent bonds.
The stairs——-A-T, G-C base pairs joined by hydrogen bonds.
how are the Railings —–( sugar/ phosphate backbone)
Alternating units of deoxyribose and phosphate
with covalent bonds
How are the The stairs——-A-T, G-C base pairs joined
with hydrogen bonds
A-T and G-C arise from their chemical structure
A (adenine) and G (guanine) are purines
T ( thymine) and C ( cytosine) are pyrimidines
A———————–T
G———————-C
(PURINES) (PYRIMIDINES)
Purines
bases with a double ring structure( Adenine
pyrimidines
bases with a single ring structure
A-T and G-C are the same width because
Each pair includes a purine and a pyrimidine
Explain the pairings of the bases
A-T and G-C
Each pair has equal amounts of each base
The pairs have the same width because each contain a purine and a pyrimadine
The two strands of DNA are COMPLEMENTARY because
The sequence of each strand defines the sequence of the other
( A on one strand means a T on the other)
( G on one strand means a C on the other)
Why is complementary base important
It is the basis of gene function
How are the two strand physically arranged
. They go in opposite directions
The two strands are parallel but tail to head ( anti parallel)
The designation of the opposite end of the double helix
3 prime ( ending with a 3' carbon) 5 prime ( ending with a 5'carbon)
What are the components of DNA and its three-dimensional structure
The components of a DNA molecule are nucleotides. These are composed of a deoxyribose sugar bonded to a phosphate and a nucleotide base (adenine, thymine, cytosine, or guanine). The three-dimensional structure of DNA is a double helix, which resembles a twisted ladder.
What evidence enabled Watson and Crick to decipher the structure of DNA
The evidence included Rosalind Franklin’s X-ray diffraction photo of a crystal of DNA, plus Erwin Chargaff’s work that showed that DNA contains equal amounts of adenine and thymine and equal amounts of cytosine and guanine.
Identify the 3′ and 5′ ends of a DNA strand
The 5’ end has the 5th numbered carbon in deoxyribose facing out and leading with a phosphate group attached, and the 3’ end has the 3rd numbered carbon leading with no phosphate, just the OH attached to the carbon.
3’ and 5’ are numbersmthat chemist assign to carbon atoms in deoxyribose
