Molecular Structure of DNA

Study Notes

Structure

DNA (Deoxyribonucleic acid) is a double-stranded helix composed of:
- Two complementary strands of nucleotides
- Sugar molecules (deoxyribose) and phosphate groups
- Nitrogenous bases: adenine (A), guanine (G), cytosine (C), and thymine (T)
The sugar and phosphate molecules make up the backbone of the DNA, while the nitrogenous bases project inward from the backbone and pair with each other in a complementary manner:
- A pairs with T (two hydrogen bonds)
- G pairs with C (three hydrogen bonds)

Replication

DNA replication is the process of creating an exact copy of a DNA molecule
It occurs during cell division and is initiated by an enzyme called helicase
The process involves:
1. Unwinding of the double helix
2. Binding of primers to the template strands
3. Synthesis of new DNA strands by DNA polymerase
4. Proofreading and editing to correct errors
The resulting DNA molecule is identical to the original, with each new strand containing one old strand (template) and one new strand synthesized during replication

Genetic Code

The genetic code is the set of rules that dictates how the sequence of nitrogenous bases in DNA is translated into a sequence of amino acids in proteins
The code is based on triplets of nucleotides called codons
There are 64 possible codons, but only 20 amino acids are commonly used in proteins
The genetic code is degenerate, meaning that more than one codon can code for the same amino acid
The code is also universal, meaning that it is the same for all living organisms

Mutations

A mutation is a change in the DNA sequence of an organism
Types of mutations:
- Point mutations: a change in a single nucleotide
- Frameshift mutations: an insertion or deletion of one or more nucleotides, leading to a change in the reading frame of the genetic code
- Chromosomal mutations: changes in the number or structure of chromosomes
Mutations can occur spontaneously or be induced by environmental factors such as radiation or chemicals
Mutations can have significant effects on the function and structure of proteins, leading to changes in the phenotype of an organism

Gene Expression

Gene expression is the process by which the information in a gene's DNA is converted into a functional product, such as a protein
The central dogma outlines the flow of genetic information:
1. Transcription: DNA is transcribed into RNA
2. Translation: RNA is translated into protein
Gene expression is regulated by a variety of mechanisms, including:
- Transcriptional regulation: controlling the transcription of DNA into RNA
- Post-transcriptional regulation: controlling the processing and translation of RNA into protein
- Epigenetic regulation: controlling gene expression through modifications to DNA or histone proteins

DNA Structure

DNA is a double-stranded helix composed of two complementary strands of nucleotides, sugar molecules (deoxyribose), and phosphate groups
Nitrogenous bases include adenine (A), guanine (G), cytosine (C), and thymine (T)
Sugar and phosphate molecules make up the backbone of the DNA, while nitrogenous bases project inward and pair with each other in a complementary manner
Adenine (A) pairs with thymine (T) using two hydrogen bonds, and guanine (G) pairs with cytosine (C) using three hydrogen bonds

DNA Replication

DNA replication is the process of creating an exact copy of a DNA molecule, occurring during cell division
Helicase initiates the process, which involves unwinding the double helix, binding of primers, and synthesis of new DNA strands by DNA polymerase
Proofreading and editing ensure that errors are corrected during the replication process
The resulting DNA molecule is identical to the original, with each new strand containing one old strand (template) and one new strand synthesized during replication

Genetic Code

The genetic code is the set of rules that dictates how the sequence of nitrogenous bases in DNA is translated into a sequence of amino acids in proteins
The code is based on triplets of nucleotides called codons, with 64 possible codons and 20 commonly used amino acids
The genetic code is degenerate, meaning that more than one codon can code for the same amino acid
The code is universal, meaning that it is the same for all living organisms

Mutations

A mutation is a change in the DNA sequence of an organism, which can occur spontaneously or be induced by environmental factors
Types of mutations include point mutations, frameshift mutations, and chromosomal mutations
Mutations can have significant effects on the function and structure of proteins, leading to changes in the phenotype of an organism

Gene Expression

Gene expression is the process by which the information in a gene's DNA is converted into a functional product, such as a protein
The central dogma outlines the flow of genetic information: transcription (DNA to RNA), and translation (RNA to protein)
Gene expression is regulated by transcriptional regulation, post-transcriptional regulation, and epigenetic regulation

Description

Understand the composition and structure of DNA, including the double-stranded helix, nucleotides, sugar molecules, phosphate groups, and nitrogenous bases. Learn how the sugar and phosphate molecules form the backbone and how the nitrogenous bases pair with each other.