BIOLOGY- U4T1 DNA structure + replication

What does DNA stand for?

Deoxyribonucleic acid

What is the structure of DNA?

A double-stranded molecule twisted into a double helix

What is DNA?

A type of nucleic acid that is responsible for storing genetic information in cells. It acts as an instruction manual that is needed for growth, survival and replication. 

Describe the structure + features of DNA in prokaryote cells?

Prokaryotic cells (Bacteria and Archaea) contain a small amount of DNA that is unbound and found in the cytoplasm. Their DNA consists of a single, circular chromosome and may include small circular plasmids. It has no introns and is not associated with histone proteins (though Archaea have histone-like proteins).

Describe the structure + features of DNA in eukaryote cells?

Eukaryotic cells contain a large amount of DNA that is bound to histone proteins and forms linear chromosomes located in the nucleus. DNA is also present as unbound circular DNA in mitochondria and chloroplasts.

Outline the structural hierarchy of genetic material in eukaryotes.

Nucleus → Chromosomes → DNA wrapped around histones → Genes → Introns and Exons → Nucleotides.
This shows how DNA is progressively organised from the largest structure (nucleus) down to its smallest unit (nucleotide).

What are introns and exons?

• Introns are non-coding regions of a gene that are removed during RNA processing.

• Exons are coding regions that remain and are expressed in the final mRNA to produce proteins.

What are the building blocks of DNA?

Neucleotides

What are the three components of a DNA nucleotide?

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

What are the four nitrogenous bases in DNA?

Adenine, Thymine, Cytosine, Guanine 

What are the complementary base pairings in DNA?

A-T and C-G

What holds the 2 DNA strands together?

Weak, base-specific hydrogen bonds between complementary base pairings

How many hydrogen bonds form between A-T and C-G

• A-T 2 hydrogen bonds

• C-G 3 hydrogen bonds

What is RNA, and the structure and complementary base pairings?

RNA is a type of nucleic acid that is responsible for interpreting genetic information (from DNA) into proteins.

RNA is single stranded and includes a specific type of nucleotide called ribonucleotide that includes 

• Ribose

• Phosphate group

•  Nitrogenous base

The complementary base pairings are G-C and A-U (Uracil)

What are the steps in DNA replication

1. Unravelling the DNA

2. Building a new DNA strand

3. Forming the DNA backbone

What does helicase do in DNA replication?

Unwinds the double helix and separates the two strands by breaking hydrogen bonds.

What does DNA polymerase do in DNA replication? 

Synthesizes new complementary strands by adding nucleotides to the exposed bases.