Unit 3-Module 1: DNA Structure

What is a nucleotide?

DNA’s building block: sugar, phosphate, and a nitrogenous base.

What sugar is found in DNA?

Deoxyribose.

Which four bases are found in DNA?

Adenine (A), thymine (T), cytosine (C), guanine (G).

What are the DNA base-pairing rules?

A pairs with T; C pairs with G.

What holds complementary DNA bases together?

Hydrogen bonds: A–T has 2; C–G has 3.

What is DNA’s shape called?

A double helix, like a twisted ladder.

What makes up DNA’s outer backbone?

Alternating deoxyribose sugars and phosphate groups.

What does antiparallel mean in DNA?

The two strands run in opposite directions: 5′→3′ and 3′→5′.

What is Chargaff’s rule?

In double-stranded DNA, A = T and C = G.

How does DNA differ from RNA?

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

What are the three parts of a DNA nucleotide?

A phosphate group, deoxyribose sugar, and nitrogenous base.

Which bases are purines?

Adenine and guanine; have two rings.

Which bases are pyrimidines?

Cytosine and thymine; RNA also has uracil. Have one ring.

What is a gene?

A segment of DNA that contains instructions for a functional product, often a protein.

What is a chromosome?

A long DNA molecule packaged with proteins that carries genetic information.

What is a trait?

An inherited characteristic, such as eye color or blood type.

What is the genetic code?

The instructions in DNA/RNA used to build proteins.

What is a polypeptide chain?

A chain of amino acids that folds to form a protein.

What did Rosalind Franklin contribute to DNA discovery?

Her X-ray diffraction image, Photo 51, provided evidence that DNA is helical.

What did Watson and Crick propose?

A model of DNA as a double helix made of two complementary strands.

What did Maurice Wilkins contribute to DNA research?

He helped study DNA using X-ray diffraction methods.

What is complementary DNA sequence?

The matching strand formed using A–T and C–G pairing rules.

What is the complementary strand to A-T-C-G?

T-A-G-C.

What does DNA replication do?

Makes a copy of DNA before a cell divides.

Why is base pairing important in replication?

Each original strand helps guide formation of a complementary new strand.

What type of bond connects sugar and phosphate along one DNA strand?

Strong covalent bonds form the sugar-phosphate backbone.

What type of bond connects paired DNA bases across the strands?

Hydrogen bonds.

Which DNA base pairs have three hydrogen bonds?

Cytosine and guanine (C–G).

Which DNA base pairs have two hydrogen bonds?

Adenine and thymine (A–T).

Why is DNA important to organisms?

It stores hereditary information and instructions for cell functions and traits.