Structure of DNA - GCSE Biology
Introduction
- In our body, all the cells know what, when, and how to do.
- This is because there are instructions present inside the nucleus of each cell.
- It is called genetic information and is stored in the form of DNA.
- All forms of life having cells as their basic unit have DNA as their genetic material.
- However, certain viruses use RNA for the same purpose.
Real-life Examples:
What is DNA
- DNA is an abbreviation for Deoxyribonucleic Acid.
- It is the genetic material in most organisms.
- It is the carrier of the genetic information from one generation to another.
- In the nucleus, DNA is condensed with proteins and is present in the form of chromosomes.
Overall Structure of DNA
- A DNA molecule is a double-stranded structure.
- Both the strands spiral around each other, connected by base pairs in a double helix structure.
- The backbone of the strands is made of the sugars and phosphate groups.
- These two are attached to one of the four bases: Adenine (A), Thymine (T), Cytosine (C), and Guanine (G).
- Together, a base, a sugar, and a phosphate group form a nucleotide.
Double-Stranded Structure and Hydrogen Bonding
- The bases, A, T, C, and G, are slightly electrically charged.
- As opposite charges attract each other, they form weak attractive forces known as hydrogen bonds.
- Therefore, Cytosine forms three hydrogen bonds with Guanine, and Adenine forms two hydrogen bonds with Thymine.
- These weak hydrogen bonds hold two sugar and phosphate group backbones together, making DNA double-stranded.
Base Pairing & The DNA Code
- DNA has four bases in it.
- Bases form pairs, A with T, and G with C, known as complementary base pairs.
- These four bases come together in different sequences in a three-letter codon and encode for a protein.
- These coded instructions are present in genes.
- Difference in the order of the bases causes us all to have different genes.
- All the individuals have different DNA except for identical twins.
- Scientists can find an individual’s identity as parents transfer DNA to their offspring.
Organization of DNA
- Since DNA is a polymer (a long chain of nucleotides joined together), it cannot simply fit inside a cell.
- Therefore, a long molecule of DNA is wrapped around proteins, named as histones, to make chromatin.
- The chromatin coils numerous times to form a chromosome.
- In prokaryotes, for example, bacteria, DNA lies freely in the cytoplasm.
- However, in eukaryotes, like plants and animals, DNA is present enclosed in the nucleus.
Organization of DNA in Prokaryotic Cells
- In prokaryotic cells, DNA is found free in the cytoplasm.
- It is in the form of one circular DNA molecule, chromosomal DNA.
- There is no association of DNA with histone proteins.
- Other than this, plasmids are also found in these cells.
- These are small, circular DNAs that carry extra genes.
Organization of DNA in Eukaryotic Cells
- In eukaryotic cells, DNA is present inside the nucleus.
- Unlike prokaryotes, its shape is linear.
- It is condensed with histone proteins to form chromatin.
- Other than nuclear DNA, mitochondria and chloroplasts have their own DNA.
Frequently Asked Questions
Solution:
DNA (Deoxyribonucleic Acid) is the genetic material found in cells.
Solution:
The shape of DNA is a double helix, which looks like a twisted ladder.
Solution:
A nucleotide is the basic building block of DNA. Each nucleotide has: a deoxyribose sugar, one nitrogen base, and a phosphate group.
Solution:
Weak hydrogen bonds hold two DNA strands together.
Solution:
Four bases found in DNA are Adenine (A), Thymine (T), Guanine (G), Cytosine (C).
Solution:
The specific base pairing between Adenine and Thymine, and Guanine and Cytosine is known as complementary base pairing.
Solution:
A gene is a short section of DNA that codes for a specific protein.
Solution:
Human cells have 23 pairs of chromosomes, that is, 46 in total.