Chapter 4: DNA & Gene Expression

What is DNA?

The molecular script of life. Every living cell carries its won copy of this script, written in a four-letter chemical code that determines traits, diseases, and inheritance. Understanding its structure allows biotechnology to read, copy, and edit the language of heredity.

What is DNA made up of?

Two long chains of nucleotides that wind around each other to form a double helix. Each nucleotide has three parts: a phosphate group, a deoxyribose sugar, and a nitrogenous base.

What shape is DNA?

The helix shape ensures stable storage of genetic information and faithful replication.

What is each nucleotide made up of?

Each has three parts: a phosphate group, a deoxyribose sugar, and a nitrogenous base.

What is the backbone of DNA?

The sugar and phosphate form the backbone.

How are the rungs of the ladder connected together?

The hydrogen bonds connect the two strands.

What are the four nitrogen bases?

Adenine, Thymine, Cytosine, Guanine.

How do the nitrogenous bases of DNA pair?

Bases pair by hydrogen bonding. Adenine always pairs with Thymine (two hydrogen bonds) and Cytosine always pairs with Guanine (three hydrogen bonds).

What do the sequence of bases code?

It encodes the instructions for building proteins.

How does Biotechnology use DNA’s stability and reproducibility?

Biotechnology uses DNA for PCRs, Gene Sequencing, and Genetic Engineering.

What does understanding the structure of DNA allow?

Knowing how DNA’s structure dictates its functions is the foundation for modern biotechnology and genetic medicine.

When does DNA replication occur?

Occurs in the S phase of the cell cycle.

What is semiconservative replication?

Each new molecule contains one old strand and one new strand.

How does the DNA double helix unwind?

Enzymes separate the strands.

What is the replication fork?

Marks the region where the DNA is opening.

What is the leading strand?

The complementary strand that is built continuously.

What is the lagging strand?

The strand of DNA that is built in fragments.

What type of DNA does bacteria have?

Bacteria has a singular, circular chromosome.

What is DNA polymerase?

A type of enzyme that attaches at the origin of replication to separate the DNA strands and building new complimentary strands.

What is the Origin Recognition Complex?

Detects and binds to the Origin of Replication (specific DNA sequence). It also marks where replication begins.

What is Helicase?

Unwinds the DNA double helix by breaking hydrogen bonds between base pairs.

What is the purpose of the template DNA?

Original DNA strands that serve as guides to build complementary new strands.

What is the Replication bubble?

Formed where DNA strands separate and expands as replication proceeds in both directions.

What is the replication fork?

The “Y” shaped region where DNA is actively unwound and copied.

What are topoisomerases?

Prevent DNA from unwinding ahead of the fork by making temperature cuts. Essential for relieving torsional stress during replication.

What are single-stranded binding proteins?

Bind to unpaired DNA strands to keep them from reattaching and stabilizes the open replication fork.

What are RNA primers?

Short RNA sequences synthesized to start DNA synthesis.

What is primase?

Enzyme that synthesizes RNA primers on both strands.

What are Okazaki fragments?

Short stretches of newly synthesized DNA joined later into a continuous strand.

What is DNA ligase?

Enzyme that joins Okazaki fragment and is the final step to ensuring a complete strand.

What are histones proteins?

Small, positively charged proteins that bind DNA, allowing it to coil tightly.

What are histones?

Proteins, where eight of them from a core around which DNA unwinds.

What are nucleosomes?

The basic unit of chromatin, consisting of DNA wrapped around histones.

What is chromatin?

The entire DNA-protein complex visible in the nucleus.

What are euchromatin?

Loosely packed and active chromatin.

What are heterochromatin?

Tightly packed and inactive chromatin.

Who discovered transformation?

Frederick Griffith.

When was transformation discovered?

1928

What is the end conclusion of DNA transformation?

Genetic information could be transferred between bacteria, specifically that heritable information could be passed between organisms without direct reproduction.

What is transcription?

The process where the genetic information from a segment of DNA is copied into a new molecule of messenger RNA.

What is mRNA?

A single stranded RNA copy of DNA that carries genetic information to ribosomes. Formed through transcription, DNA acts as a template for mRNA synthesis.

What is a ribose phosphate backbone?

RNA’s sugar-phosphate structure that contains ribose instead of deoxyribose.

What is a codon?

A sequence of three RNA bases that code for a specific amino acid.

What is a polypeptide?

A chain of amino acids linked by peptide bonds and fold into function proteins.

What is an enzyme?

A biological catalyst formed from the polypeptide that speeds up specific chemical reactions.

What is the central dogma of molecular biology?

The process of DNA to mRNA to Protein to Trait in molecular biology.