Enzymes
* Helicase - Unwinds the double helix by breaking hydrogen bonds between complementary bases.
* DNA polymerase - Adds complementary nucleotides to the growing DNA strand, ensuring accuracy.
* Primase - Lays down an RNA primer to start the replication process.
* Ligase - Seals gaps between Okazaki fragments on the lagging strand.
* Topoisomerase - Relieves tension in the DNA ahead of the replication fork.
STEPS
1. Initiation - DNA helicase unwinds the DNA molecule, creating a "replication fork."
2. Elongation - DNA polymerase adds nucleotides (A, T, C, G) to the exposed strands in the 5' to 3' direction.
3. Leading Strand - Replicated continuously towards the fork.
4. Lagging Strand - Replicated in fragments (Okazaki fragments), which are later joined by DNA ligase.
5. Termination - Once the entire DNA molecule is replicated, the enzymes dissociate, and the DNA strands rewind.
TRANSCRIPTION
What Happens in Transcription?
* DNA is used as a template to create messenger RNA (mRNA).
* mRNA is a copy of the gene that will be translated into a protein.
Key Points:
* RNA Polymerase unzips the DNA and creates a complementary mRNA strand.
* mRNA leaves the nucleus and enters the cytoplasm.
TRANSLATION
appens in Translation?
* mRNA is read by ribosomes to assemble a chain of amino acids.
* tRNA (transfer RNA) brings the correct amino acids to the ribosome.
Start Codon: mRNA binds to the ribosome at the start codon (AUG), signaling the beginning of protein synthesis.
Codons & tRNA: Each set of 3 mRNA bases (codon) codes for an amino acid. tRNA molecules match their anticodons to the mRNA codons and bring the corresponding amino acids.
Amino Acid Chain: Amino acids are linked together to form a protein.
Stop Codon: When a stop codon is reached, the protein is complete.
tRNA
* tRNA carries amino acids to the ribosome based on the mRNA's codon sequence.
* Each tRNA has an anticodon that matches a codon on the mRNA, ensuring the correct amino acid is added to the protein chain.
CENTRAL DOGMA
hat is the Central Dogma?
* The Central Dogma describes the flow of genetic information in cells.
* It explains how DNA is used to create proteins.
Steps in the Central Dogma:
1. DNA → RNA (Transcription)
* DNA is transcribed into mRNA in the nucleus.
* mRNA serves as the messenger that carries genetic information from DNA to the ribosome.
2. RNA → Protein (Translation)
* mRNA is translated into a protein at the ribosome in the cytoplasm.
* The sequence of mRNA codons determines the sequence of amino acids in the protein.
Key Points:
* DNA (genetic information) → mRNA (transcript) → Protein (functional product).
* The Central Dogma shows how genetic information is expressed in living organisms.
SICKLE CELL DISEASE
Sickle-cell disease is caused by a mutation in the hemoglobin gene.
This mutation results in a substitution of adenine (A) with thymine (T), causing a change in the 6th amino acid in the hemoglobin protein from glutamic acid to valine.
This change causes red blood cells to become sickle-shaped and less efficient at carrying oxygen.
POINT MUTATION
Additional Info: A point mutation is when a single base is added, changed, or deleted.
Example: Substitution mutation – a nucleotide is replaced with a different nucleotide
Effect: These mutations may have minimal effects or none at all, depending on the change. (Silent - no change, missense - 1 amino acid changed, nonsense (premature stop codon)
* Silent Mutation: No change in the amino acid sequence.
* Missense Mutation: One amino acid is replaced by another, which can affect protein function.
* Nonsense Mutation: A premature stop codon is introduced, resulting in a shortened protein that is often nonfunctional.
FRAMESHIFT MUTATION
A frameshift mutation occurs when nucleotides are inserted or deleted, altering the reading frame of the codons. This results in a completely different sequence of amino acids from the mutation point onward, often leading to a nonfunctional protein.
Types - Insertion, deletion - no stop codon, 1 amino acid deleted/added, amino acids changed after mutation
CHROMOSOMIAL MUTATION
Definition:
Chromosomal mutations involve changes to the structure or number of chromosomes. These mutations can affect large segments of DNA and may impact multiple genes.
Types of Chromosomal Mutations:
* Deletion: A section of a chromosome is lost.
* Duplication: A section of a chromosome is copied, resulting in multiple copies of a gene or region.
* Inversion: A section of a chromosome is reversed or flipped.
* Translocation: A part of one chromosome breaks off and attaches to another chromosome.
Effect on the Organism: Chromosomal mutations can cause diseases, developmental issues, or genetic disorders. The effects depend on the genes involved and the extent of the mutation.
Example:
* Down Syndrome: Caused by an extra copy of chromosome 21 (trisomy 21), leading to developmental and physical challenges.
MUTAGENS
Mutagens are agents that cause mutations. They can include chemicals, radiation, or viruses, and they damage the DNA, leading to changes in the genetic sequence.
Outcomes
Neutral Mutation - No effect on the organism.
Beneficial Mutation - May provide an advantage and become part of the species' genetic pool.
Harmful Mutation - May lead to diseases or decreased survival.
Some mutations can be passed to offspring, contributing to evolutionary changes.