Lecture 14- DNA Flashcards
What is DNA composed of?
Nucleotides
What are nucleotides composed of?
Nitrogenous base, pentose sugar (deoxyribose/ribose), & phosphate group
What was the significance of Griffith’s experiment?
Hypothesized transformation (experiment with mice and streptococcus pneumoniae)
How many common amino acids are there?
20
What was the significance of the experiments conducted by Avery, MacLeod, & McCarty?
Lysed smooth (S) cells → separated contents into biological macromolecules → tested each macromolecule for transforming ability → discovered that only DNA could transform
What was the significance of the Hershey-Chase experiment?
Discovered that bacteriophages are composed of just DNA and protein (via radioactive tracers)
What are the main classifications of nitrogenous bases?
Purines & pyrimidines
What is the difference between purines and pyrimidines?
Pyrimidines are composed of a single ring whereas purines are composed of two rings
Which nitrogenous bases are considered purines?
Adenine & guanine
Which nitrogenous bases are considered pyrimidines?
Thymine, cytosine, & uracil
What was the significance of Rosalind Franklin’s experiment?
Discovered the helical structure of DNA via x-ray crystallography
What was the significance of Erwin Chargaff’s experiment?
Discovered that there are approximately equal amounts of purines and pyrimidines in DNA
What was the significance of the discovery made by Watson & Crick?
Using Rosalind Franklin’s DNA model, Watson & Crick were able to explain how DNA could carry genetic information and how information could be replicated. Found that each rung in DNA is composed of a purine and a pyrimidine
What type of bond occurs between the sugar-phosphate backbone?
Phosphodiester linkages
What type of bond occurs between the nitrogenous bases?
Two hydrogen bonds between adenine and thymine & three hydrogen bonds between guanine and cytosine
How does dehydration synthesis occur to form bonds between the sugar-phosphate backbone?
Occurs between the free 3 hydroxyl (OH) & the free 5 phosphate
Which nitrogenous bases pair with each other?
Adenine with thymine in DNA or uracil in RNA & cytosine with guanine (in both DNA/RNA)
What does it mean that DNA replication follows a semi-conservative model?
A parental strand is used to synthesize a daughter strand
What are the steps of transcription in order?
Initiation → elongation → termination
Which event marks the start of transcription initiation?
Separation of strands & formation of replication bubble (origin of replication)
How do single-stranded binding proteins (SSBPs) aid in DNA replication?
SSBPs keep DNA strands apart
Relative to the replication bubble, in which direction does replication proceed?
Replication proceeds towards the replication forks
Which protein is responsible for unwinding the DNA helix during replication?
Helicase
What is the function of topoisomerase?
Relaxes DNA helix (provides stability to unwound DNA)
What is the function of RNA primase?
Synthesize RNA primers which allow DNA polymerase to proceed with replication
What is the end result of transcription?
Pre-mRNA
How are DNA strands oriented relative to one another?
Antiparallel
What are the modifications pre-mRNA undergoes before it is considered a mature mRNA?
Introns snipped out by spliceosome and exons are joined together. Also a 3 poly-adenine tail and 5 guanosine cap are added to the ends of the mRNA
What is added to the growing molecule during the elongation stage of DNA replication?
Nucleoside triphosphates added → forms new phosphodiester bond → releases pyrophosphates
Which enzyme is responsible for combining DNA strands back together at the end of replication?
DNA ligase
What is the lagging strand composed of?
Okazaki fragments
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