QCAA Unit 3 + 4 Biology

What is the full form of DNA?

Deoxyribonucleic acid

Where is DNA located in eukaryotic cells?

In the nucleus bound to histone proteins, and also in mitochondria and chloroplasts as circular unbound DNA.

Where is DNA located in prokaryotic cells?

In the cytosol as unbound circular DNA.

What is a nucleotide composed of?

A phosphate group, a deoxyribose sugar, and a nitrogenous base.

What are the four nitrogenous bases in DNA?

Adenine (A), Thymine (T), Guanine (G), Cytosine (C)

Which bases pair together in DNA?

Adenine with Thymine, Guanine with Cytosine

What type of bond holds complementary bases together?

Weak, base-specific hydrogen bonds

What is the role of histones?

Histones are proteins that DNA wraps around to form chromatin, helping with DNA packaging in the nucleus.

How many hydrogen bonds are between A–T and G–C?

A–T has 2 hydrogen bonds, G–C has 3 hydrogen bonds

Why are hydrogen bonds important in DNA replication?

They are weak enough to be broken during replication, allowing the strands to separate and be copied.