Theme 1B Flashcards
What are the components of DNA?
- Pentose Sugars
- Ribose used in RNA
- Deoxyribose used in DNA - Nitrogenous bases
- Adenine, Guanine, Cytosine, Thymine, Uracil - Phosphate
What are purine and pyrimidines?
Purines: have a double ring (adenine, guanine)
Pyrimidines: have a single ring (cytosine, thymine, uracil)
What is a nucleoside?
Molecules of a sugar and a base.
ex: deoxyribonucleoside: deoxyribose + purine/pyrimidine base
- Carbon 1 of pentose sugars binds to N9 of purines and N1 of pyrimidines
What is the difference between ribose and 2-deoxyribose?
Ribose has a hydroxyl group attached to carbon 2, and 2-deoxyribose has a hydrogen attached to carbon 2
What is a nucleotide?
Nucleoside molecule and a phosphate (s).
- Phosphate group attaches to the carbon 5 of pentose sugars
What is DNA?
A polymer of deoxyribonucleotides.
- Nucleotide monomers polymerize via phosphodiester bonds
- Covalent bonds form between phosphate and Carbon 3 and Carbon 5 of two pentose sugars (pentose phosphate backbone)
- Polynucleotide has polarity with Carbon 5 phosphate end and Carbon 3 OH end
What is Chargaff’s rule?
Adenine = guanine
Cytosine = thymine
Purines = pyrimidines
C + G does NOT equal A + T
- A, C, G, and T are not present in equal amounts
Who was Rosalind Franklin and what did she discover?
Discovered the structure of DNA with x-ray diffraction
- Found out DNA is cylindrical and 2nm in diameter
- Found out DNA has a periodicity of 0.34 nm (suggesting bases are stacked on top of each other)
- The x shaped pattern indicated a helical structure
What did Watson and Crick discover with Franklin’s data?
- Two strands of the phosphate-pentose backbone spiral as a double helix around a common axis
- The two strands run antiparallel
- A purine on one strand is always paired with a pyrimidine
- The backbone (exterior) is hydrophilic and the bases (interior) are hydrophobic
How are bases kept together?
Hydrogen bonds
- 3 bonds between purines
- 2 bonds between pyrimidines
What is nucleic hybridization?
Annealing strands of DNA or RNA by forming hydrogen bonds. Separating/denaturing the base pairs in DNA and then adding RNA to make DNA-RNA hybrids
What are the measurements of DNA?
- DNA is 2nm in diameter
- Distance between base pairs (periodicity) is 0.34 nm
- Each full twist of DNA is 3.4 nm
What is complementary base pairing?
Parental strands act as templates for DNA replication of new strands. The original parent strands unwind by breaking hydrogen bonds between bases
How is DNA organized is eukaryotes?
Eukaryotes of multiple linear DNA molecules in a nucleus.
- DNA usually in the form of chromatin (normal state) which is condensed
- Unwinds during replication, transcription, and translation
- Chromatin condenses further into chromosomes for mitosis/meiosis
What is a nucleosome?
Double helix wrapped twice around histone proteins.
- Repeating series of DNA molecules called 10nm chromatin fibres (beads on a string)
- Histone H1 binds linker DNA and nucleosomes to form 30nm chromatin fibres
What is euchromatin?
Regions of DNA that have lower compaction (cause used more often) and where genes are actively expressed
What is heterochromatin?
High DNA compaction where gene expression is silenced.
- Constitutive heterochromatin: DNA is almost always compact cause it is never really needed
- Facultative heterchromatin: can switch to euchromatin depending on cell type and development (sometimes needed)
Why is DNA organized into chromosomes?
- Chromosomes compact DNA so that it can fit into the cell/nucleus
- Chromsomal structure protects DNA from damage (if DNA is left as a double helix it can get tangled and knotted)
What are the origins of replication?
Multiple DNA sequences along the chromosome that initiate DNA replication
What are centromeres?
DNA sequence required for the correct segregation of chromosomes
What are telomeres?
DNA sequences located at the ends of the chromosome that prevent degradation and allow proper replication of the chromosomal ends
How is DNA organized in prokaryotes?
Prokaryotes of a single circular DNA. They use histone like proteins (HLP); there is not the same level of compaction though
What are plasmids?
They are in prokaryotes; they are small independant circular DNA molecules. Each cell can have multiple different plasmids as well as multiple copies of each. They carry a few “bonus genes” that given an advantage in a specific environment
