Theme 1B Flashcards
Structure of DNA and Chromosomes (40 cards)
3 Components of DNA
- Pentose sugar - 5’C sugar
(Ribose RNA or Deoxyribose DNA) - Nitrogenous Base
(Purine G/A or Pyrimidine C/U/T) - Phosphate
Purine
nitrogenous base
guanine or adenine
Pyrimidine
nitrogenous base
cytosine, uracil, thymine
Pentose Sugars of DNA & RNA
Ribose - has OH attached to 2’C
2-Deoxyribose - has H attached to 2’C
(know structures - slide 3)
Nitrogenous bases of DNA & RNA
DNA = ACGT
RNA = ACGU
Nucleosides?
Deoxyribonucleosides?
- molecules of sugar & a base
- 2-deoxyribose sugar + purine/pyrimidine base
Base binds to C1’ of deoxyribose/ribose
4 base + sugars:
deoxyadenosine
deoxyguanosine
deoxythymidine
deoxycytidine
(What are ribose versions of these^ and what would they look like?)
- adding OH removes “deoxy”
Nucleotides
nucleoside molecule + phosphate
- phosphate group attached to carbon - 5’ of the ribose and deoxyribose sugars
4 nucleotides:
- deoxyadenosine triphosphate (dATP)
- deoxythymidine triphosphate (dTTP)
- deoxyguanosine triphosphate (dGTP)
- deoxycytidine triphosphate (dCTP)
(adding OH instead of an H to their structures removes “deoxy” and “d”)
DNA
polymer of deoxyribonucleotides
- nucleotide monomers polymerize via phosphodiester bonds (C-O-P-O-C)
- covalent bonds form between phosphate and C-3’ and C-5’ of two pentose sugars (pentose-phosphate backbone)
- polynucleotide has polarity with a C-5 PO4 end and C-3’ OH end
- type of nucleic acid depends on sugar (DNA=deoxyribose & RNA=ribose in P-P backbone)
What is the charge of a DNA molecule
negative because of the phosphate group
What is an identifying characteristic of DNA? RNA?
has hydrogen group
has hydroxyl group
Erwin Chargaff
analyzed overall quantities of four nitrogenous bases in various organisms
Chargaff’s Rule
% A = % T
% C = % G
% Purines (A+G) = % Pyrimidine (C+T)
How did scientists know that the info coding for life is in the nitrogenous base?
sequence of nucleotides changes; everything else remains the same
hence, ACGT sequence gives the unique genotype
X-Ray diffraction studies - Rosalind Franklin & James Watson
DNA molecules were ________.
0.34 nm periodicity suggested that bases were ___________.
X-shaped pattern indicated ________.
contributed to determining 3-D structure of DNA
-cylindrical & about 2 nm in diameter
- stacked like pennies on top of each other
- helical structure
Watson proposed definitive model
(Watson & Crick)
Two strands of the phosphate-pentose backbone spiral as a ____________ about a common axis.
The two strands run _________.
Purine on one strand is always base-paired with a ________.
double helix
anti-parallel
pyrimidine
Base pairing is _________, which allows…
complimentary; determining sequence of one strand using another
What type of bonding occurs between two strands?
hydrogen bonding
Nucleic Acid Hybridization
annealing of single strands of DNA/RNA by forming H-bonds
- highly specific (strands must be complimentary)
Nucleic Acid Hybridization is _______ & ___________.
temperature-driven; concentration-dependent
DNA-RNA hybrids are found in _________, ____________, & _______.
DNA replication; transcription; reproduction of some RNA viruses.
Complementary base pairing allows _____ to act as templates for DNA replication of new strands.
Parental strands can unwind by _______________ between bases.
_____________ is where the double helix will contain a parental strand and a newly synthesized strand.
parental strands; breaking hydrogen bonds; semi-conservative replication.
How is DNA organized in prokaryotes and eukaryotes?
-DNA is associated with proteins and organized into structures called chromosomes
Chromatin
given region of DNA with its associated proteins on a chromosme
Chromosomes can be ________ & ___________
can be linear or circular
- prokaryotes have one and other small independent circular DNA called plasmids in cytoplasm
- eukaryotic chromsomes are linear and enclosed in nucleus
