Nucleic Acids-DNA and RNA Flashcards
DNA Structure
Double helix structure, made of two strands
Located in the nucleus (in eukaryotes)
Stores genetic information for cellular function and reproduction
Contains deoxyribose sugar in each nucleotide
Provides a permanent genetic code for cells and organisms
RNA Structure
Single-stranded molecule
Functions mostly outside the nucleus in eukaryotes (e.g., cytoplasm)
Transfers genetic information for protein synthesis
Contains ribose sugar in each nucleotide
Does not provide a permanent code, except in RNA viruses
Nucleotide Structure
Each nucleotide consists of a phosphate group, sugar (ribose or deoxyribose), and a nitrogenous base
Nucleotides are monomers for polymers like DNA and RNA
DNA nucleotides contain deoxyribose; RNA nucleotides contain ribose
Nitrogenous Bases
Purines (2 rings): Adenine (A), Guanine (G)
Pyrimidines (1 ring): Cytosine (C), Thymine (T, in DNA), Uracil (U, in RNA)
Nitrogenous Base Pairing
DNA: Adenine pairs with Thymine (A-T), and Cytosine pairs with Guanine (C-G)
RNA: Adenine pairs with Uracil (A-U), and Cytosine pairs with Guanine (C-G)
Pentose Sugar in DNA & RNA
Deoxyribose (DNA): Lacks an OH group on Carbon 2 (only H present)
Ribose (RNA): Has an OH group on Carbon 2
Carbon 1: Binds with the nitrogenous base
Carbon 3: Always OH
Carbon 5: Binds with the phosphate group
Phosphate Group
The phosphate group has a negative charge that makes DNA and RNA molecules negatively charged
Binds to Carbon 5 of the sugar, linking to the next nucleotide’s Carbon 3 through phosphodiester bonds
Forms the sugar-phosphate backbone of DNA and RNA, providing structural stability
Complementary Base Pairing
Bases pair with hydrogen bonds:
A-T in DNA with 2 hydrogen bonds
C-G in both DNA and RNA with 3 hydrogen bonds
This base pairing stabilizes the DNA double helix structure and enables accurate replication
Antiparallel Arrangement
DNA strands run in opposite directions:
One strand runs 5’ to 3’
The other strand runs 3’ to 5’
This arrangement is essential for DNA replication and stability
Chargaff’s Rule
In DNA, % of Adenine (A) = % of Thymine (T) and % of Guanine (G) = % of Cytosine (C)
A-T and C-G base pairing explains this rule, crucial for DNA structure and replication
Hershey-Chase Experiment
Proved DNA is the genetic material
Used bacteriophages (viruses) with DNA labeled with radioactive phosphorus (³²P) and protein labeled with radioactive sulfur (³⁵S)
Why is the anti-parallel structure of DNA important?
The anti-parallel structure enables complementary base pairing, stabilizes the double helix, and ensures accurate DNA replication.
It also directs transcription, allowing RNA polymerase to read one strand in the 3’ to 5’ direction, which is necessary for synthesizing mRNA in the 5’ to 3’ direction. This orientation is crucial for translation since mRNA is read by ribosomes from 5’ to 3’ to build proteins correctly.
