A1.2 Nucleic Acids

What is the genetic material of all living organisms?

DNA (deoxyribonucleic acid). Some viruses use RNA, but viruses are not considered living

Why are viruses not alive?

They lack cells, metabolism, homeostasis, growth, and self-reproduction. They replicate only in host cells

What are the three parts of a nucleotide?

Pentose sugar (ribose or deoxyribose), phosphate group (acidic, negatively charged), nitrogenous base

Which bases are found in nucleotides?

DNA: A, T, C, G. RNA: A, U, C, G.

How is the sugar-phosphate backbone formed?

Nucleotides join by condensation reactions, forming covalent bonds between sugar and phosphate

Why is the sugar-phosphate backbone important?

It creates a strong, continuous covalently bonded chain, protecting genetic information

How do bases form a code?

The sequence of nitrogenous bases stores information that determines protein synthesis

How is RNA formed?

By condensation of nucleotide monomers into a single-stranded polymer

Which base is unique to RNA?

Uracil replaces thymine

What is DNA structure?

A double helix of two antiparallel strands with sugar-phosphate backbones and hydrogen bonds between complementary bases

What are complementary base pairs?

Adenine-Thymine, Cytosine-Guanine

What bonds link bases?

Hydrogen bonds

What bonds link backbone?

Covalent bonds between sugar and phosphate

What are the main differences between DNA and RNA?

DNA: double-stranded, deoxyribose sugar, thymine. RNA: single-stranded, ribose sugar, uracil

How does complementary base pairing enable replication?

Each base only pairs with its complement, ensuring accurate copying of DNA

How does complementary base pairing enable expression?

It allows transcription into RNA by matching complementary bases

Why can DNA store limitless information?

Any base sequence is possible along DNA strands. With 4 bases, combinations grow exponentially

How much information can DNA store?

Up to 215 petabytes (215 million GB) per gram of DNA

How long is DNA in one human cell?

About 2 meters of DNA stored in 23 pairs of chromosomes

How many nucleotides in human chromosome 1?

Approx. 249 million nucleotides

What is the genetic code?

A universal set of codons where groups of 3 bases code for one amino acid

Why is the genetic code evidence of common ancestry?

Almost all organisms share the same genetic code, showing universality

Example of genetic code universality?

Genes from fireflies inserted into plants make them glow.

What is an example of viruses using RNA?

Coronavirus 2019

What is an example of RNA nitrogen bases?

A, U, C, G

What is an example of DNA nitrogen bases?

A, T, C, G

What is an example of a universal genetic code experiment?

Transferring firefly genes into plants to produce glowing plants

Why is DNA considered the genetic material of life?

Because it stores hereditary information and codes for proteins, which determine structure and function in organisms

Why are viruses not considered living organisms?

They lack cells, metabolism, homeostasis, and independent reproduction; they require a host cell to replicate

How does the sugar-phosphate backbone protect genetic information?

The strong covalent bonds in the backbone shield the reactive nitrogenous bases inside

Why does RNA contain uracil instead of thymine?

Uracil is energetically cheaper to produce and is suitable for RNA's short-term roles, while thymine is more stable for long-term DNA storage

How does complementary base pairing ensure accurate DNA replication?

A always pairs with T, C always with G → the sequence of one strand determines the other, ensuring an exact copy

Why is antiparallel strand arrangement important in DNA?

It allows hydrogen bonds to form properly between complementary bases, stabilizing the double helix

Why is RNA single-stranded while DNA is double-stranded?

RNA's single strand allows flexibility in functions (mRNA, tRNA, rRNA), while DNA's double-stranded structure provides stable, long-term information storage

Why can DNA store virtually limitless information?

Any sequence of 4 bases (A, T, G, C) can be arranged in countless ways; longer molecules exponentially increase possible sequences

How does the universality of the genetic code support evolution?

All organisms use the same codons for amino acids, showing they share a common ancestor

Example of universality of the genetic code?

Genes from fireflies inserted into plants make them glow, proving DNA works across species

What does 5' to 3' directionality mean in DNA/RNA?

Nucleotides connect between the 3' carbon of one sugar and the 5' carbon of another, forming phosphodiester bonds

Why is directionality important in replication?

DNA nucleotides can only be added to the 3' end; both strands act as templates

Why is directionality important in transcription?

RNA nucleotides are added to the 3' end of mRNA; only one strand is used as a template

Why is directionality important in translation?

Ribosomes move along mRNA in the 5' → 3' direction to build polypeptides

What are purines?

Nitrogenous bases with two rings: adenine (A) and guanine (G)

What are pyrimidines?

Nitrogenous bases with one ring: cytosine (C), thymine (T), and uracil (U in RNA)

Why must purines pair with pyrimidines?

Only purine-pyrimidine pairs fit inside the helix without bulges or gaps, ensuring stability

How does purine-pyrimidine pairing affect DNA?

It maintains uniform width and geometry of the DNA double helix

What is a nucleosome?

A DNA molecule wrapped around a core of eight histone proteins, linked by an H1 histone and linker DNA

What is the function of nucleosomes?

They supercoil and compact DNA so it fits in the nucleus, protect DNA from damage, and regulate gene expression and replication

When does supercoiling occur?

Mostly during prophase of mitosis and meiosis

Why are histones positively charged?

Their positive amino acids interact with negatively charged DNA, stabilizing the structure

What question did the Hershey-Chase experiment answer?

Whether DNA or protein is the genetic material

How did Hershey and Chase label DNA and proteins?

They used radioactive phosphorus-32 (in DNA) and sulfur-35 (in proteins)

What did Hershey and Chase observe?

Only DNA entered bacteria from phages and directed viral replication

What was the conclusion of Hershey-Chase?

DNA, not protein, is the genetic material of life

What did Chargaff's data show?

Across species, the amount of adenine ≈ thymine and cytosine ≈ guanine

How did Chargaff disprove the tetranucleotide hypothesis?

He showed DNA base composition varies between species and is not a simple repeating sequence

What does Chargaff's rule support?

Complementary base pairing (A with T, G with C)

Example of a virus studied for genetic material?

T2 bacteriophage in the Hershey-Chase experiment

Example of DNA packaging?

Supercoiled chromosomes in eukaryotic nuclei

Example of Chargaff's principle in numbers?

In humans, %A ≈ %T and %C ≈ %G, but proportions differ from other species