DNA, RNA, and Mutations: The Building Blocks of Life
DNA and RNA: The Molecules of Life
DNA
Chemical Composition
Deoxyribonucleotides consisting of:
- Phosphate
- Deoxyribose
- Nitrogenous bases: Adenine (A), Thymine (T), Guanine (G), Cytosine (C)
Molecular Structure
Double-stranded helix
Types
- Nuclear DNA: Forms chromatin
- Mitochondrial DNA: Found in mitochondria
- Plastid DNA: Found in chloroplasts
Cell Location
- Nucleus
- Mitochondria
- Chloroplasts
Function
Contains the organism’s genetic information.
RNA
Chemical Composition
Ribonucleotides consisting of:
- Phosphate
- Ribose
- Nitrogenous bases: Adenine (A), Uracil (U), Guanine (G), Cytosine (C)
Molecular Structure
Single-stranded
Types
- Messenger RNA (mRNA)
- Transfer RNA (tRNA)
- Ribosomal RNA (rRNA)
Cell Location
In the cytoplasm, free or associated with ribosomes
Function
Synthesizes proteins according to the genetic information found in DNA.
DNA Replication: Copying the Blueprint
When a cell divides, both resulting daughter cells must receive identical genetic information. To achieve this, DNA replicates itself in a process called replication. This process occurs exclusively in DNA and takes place within the cell’s nucleus. From one initial DNA molecule, two identical molecules are produced.
Replication must be precise to ensure that daughter cells receive identical DNA molecules with the same genetic information. The new molecules consist of two strands: one strand from the original DNA and a complementary new strand identical to the original. This process is known as semiconservative replication.
Central Dogma of Molecular Biology
The central dogma of molecular biology describes the flow of genetic information within a biological system. It involves three key processes:
Replication
The process of duplicating a DNA molecule. It takes place in the nucleus.
Transcription
The process of synthesizing a messenger RNA (mRNA) molecule using a DNA fragment as a template. It takes place in the nucleus.
Translation
The process of synthesizing a protein using the information contained in the mRNA. It takes place in the ribosomes.
Transcription in Detail
Transcription is the process of copying a portion of the genetic information from its original DNA form into mRNA. This process occurs in the cell’s nucleus. The mRNA is then released into the cytoplasm through pores in the nuclear membrane.
The released mRNA is complementary to the transcribed DNA fragment, representing the sequence that codes for a particular protein the cell may need.
Translation in Detail
Translation is the process of synthesizing proteins using the information contained in mRNA molecules formed during transcription. This process takes place in the ribosomes.
Elements required for translation:
- An mRNA molecule created from the transcription of a DNA fragment
- Ribosomes
- Transfer RNA (tRNA): RNA molecules that carry amino acids to the ribosomes. Each type of amino acid is transported by a specific type of tRNA.
- Free amino acids in the cytoplasm
Mutations: Changes in the Genetic Code
DNA is passed down from one generation to the next. During this process, genes can undergo unexpected and random changes called mutations. Only mutations that affect a specific characteristic are noticeable. Mutations can be inherited by offspring.
Mutations can originate spontaneously (spontaneous mutations) or be induced by external factors.
Types of Mutations
Mutations can be classified based on various factors:
- Type of cell affected: Somatic, germinal
- Cause: Spontaneous, induced
- Effects: Beneficial, neutral, harmful
- Resulting alleles: Dominant, recessive
- Type of genetic alteration: Gene, chromosomal, genomic
Mutations Based on Genetic Alteration
Gene or Molecular Mutations
- Affect the chemical structure of genes
- Lead to changes in the amino acid sequence that forms a protein
- Alter the way the protein functions
Chromosomal Mutations
- Affect the structure of chromosomes
- Can duplicate, eliminate, or change fragments of chromosomes
- Perceptible using a microscope
- Occur in some tumors
Genomic or Numeric Mutations
- Affect the number of chromosomes
- Aneuploidy: Lack or excess of chromosomes
- Euploidy: The diploid set of chromosomes is affected, resulting in 3n, 4n, 5n… chromosomes instead of 2n
Mutations Based on Cause
Physical Mutagens
- Radiations that can alter DNA
- Most important: UV rays, gamma rays, X-rays, beta rays
Chemical Mutagens
– are chemical compouds that alter nucleotides from DNA; most important ones are dyes, some pesticides, pollutants, nicotine, drugs (LSD). Biologicacl mutagens – Viruses; viruses that have genomes with fragments of another cell, these are introduced into the organism they infect, and modify DNA. Transposons; are mobile segments of DNA that change position, altering original DNA.