Genetics, Mutations,DNA Replication, Everything Genes

Question 1

Mutagenic factors are factors that can cause mutations.
Genetic code means The genetic code is a set of rules defining how the four-letter code of DNA is translated into the 20-letter code of amino acids, which are the building blocks of proteins.

The genetic code is a set of rules that dictates how the information in DNA (or RNA) is translated into the sequence of amino acids that make up proteins. It essentially acts as a translator, converting the four-letter alphabet of DNA (A, C, G, T) into the 20-letter alphabet of amino acid

Question 2

Dna polymerase 1,2 are repairers
3 is mainly for replication

CG has a higher energy cuz it’s triple bonded

Pre MRNA before RNA during transcription
Introns are non coding but exons do the coding
mRNA has the codons
tRNA carries anti codons
Degeneracy of the codon.
AUG is the start codon
So genetic code helps you know which codons are coding for particular amino acids.

Truncated polypeptide leading to loud not silent defective enzymes.

De novo means your parents don’t have it but somehow you get it.

Types of mutation

What are point mutations and types
What type is in phenylketonuria and sickle cell?

Jumping genes : examples of mutagenic factors

Shine delagno or soemthing

Answer 2

Point mutation is a genetic mutation where a single nucleotide base in the DNA sequence is changed, inserted, or deleted.

Types of point mutations:
1. Substitution – One base is replaced by another.
• Silent: No change in the amino acid.
• Missense: Changes the amino acid.
• Nonsense: Creates a stop codon (premature stop).
2. Insertion – One base is added.
3. Deletion – One base is removed.

Example:

Normal DNA:
A T G C C A
Mutation (Substitution):
A T A C C A

Phenylketonuria (PKU) is caused by a point mutation in the gene that makes the enzyme phenylalanine hydroxylase (PAH).

Here’s how it works:
• The PAH enzyme normally converts phenylalanine (an amino acid from food) into tyrosine.
• A point mutation in the PAH gene (usually a missense mutation) changes just one base.
• This leads to a defective or non-functional enzyme.
• As a result, phenylalanine builds up in the body, causing brain damage if untreated.

Example mutation:

One common PKU mutation:
G → A substitution at a specific site changes the codon, replacing one amino acid with another, damaging enzyme function.

Here are common examples of each type of point mutation and the diseases they cause:

1. Silent Mutation
   • Definition: Base change, no change in amino acid.
   • Common Example:
   • No major disease, but seen in some cancer genes (e.g., silent mutations in TP53).
   • Often found in healthy people too.
2. Nonsense Mutation
   • Definition: Base change leads to a stop codon.
   • Common Example:
   • Duchenne Muscular Dystrophy – Stops dystrophin production early.
   • Beta-thalassemia – Stops hemoglobin beta chain early.
3. Insertion Mutation (Frameshift)
   • Definition: Extra base shifts all codons.
   • Common Example:
   • Tay-Sachs Disease – Insertion in HEXA gene.
   • Huntington’s Disease – Involves repeated insertions (CAG repeats).
4. Deletion Mutation (Frameshift)
   • Definition: One base deleted, shifts reading frame.
   • Common Example:
   • Cystic Fibrosis – Most common cause is ΔF508 (3-base deletion, not frameshift), but single-base deletions can cause frameshifts.
   • Tay-Sachs Disease – Some forms caused by single-base deletion.

Would you like a simplified chart for memorization?

Question 3

1. What are purines and pyrimidines? What is a hétérocycle?
2. What atoms do purines and pyrimidines contain in their rings?
3. Which is larger: purines or pyrimidines and why?
4. Which nitrogenous bases are purines?
5. Which nitrogenous bases are pyrimidines?
6. What is unique about the naming length of purines and pyrimidines?
7. How are the rings of purines and pyrimidines numbered?
8. Where does the sugar attach in pyrimidines and in purines?
9. How many nitrogen atoms are in purines and how many in pyrimidines?
10. Which of them has two rings? Purines or pyrimidines

Answer 3

1. What are purines and pyrimidines?
   Purines and pyrimidines are nitrogen-containing heterocycles that form the nitrogenous bases of nucleotides.

A cycle is a ring.
• A heterocycle is a ring made of carbon atoms plus other atoms, like nitrogen.
• So a nitrogen-containing heterocycle is a ring that has both carbon and nitrogen atoms in it.

A.Carbocycle or cyclic compound = ring with only carbon
Examples:
• Cyclohexane (6 carbon atoms in a ring)
• Benzene (a 6-carbon ring with alternating double bonds

B.Heterocycle = ring with carbon + other atoms (like N, O, S)

2. What atoms do purines and pyrimidines contain in their rings?
   They contain carbon and nitrogen atoms in their cyclic structures.
3. Which is larger: purines or pyrimidines?
   Purines are larger than pyrimidines because purines have a two-ring structure, while pyrimidines have a single ring.
4. Which nitrogenous bases are purines?
   Adenine (A) and guanine (G) are purines.
5. Which nitrogenous bases are pyrimidines?
   Cytosine (C), thymine (T), and uracil (U) are pyrimidines.
6. What is unique about the naming length of purines and pyrimidines?
   The smaller pyrimidine molecule has the longer name, while the larger purine molecule has the shorter name.
7. How are the rings of purines and pyrimidines numbered?
   The six-atom rings are numbered in opposite directions: purines clockwise from N9, and pyrimidines counterclockwise from N1.

N1 refers to the first nitrogen atom in the ring structure of a nitrogenous base, specifically in pyrimidines.
• In pyrimidines (cytosine, thymine, uracil), the ring atoms are numbered starting at N1, which is the nitrogen at the bottom left of the single six-membered ring, and the numbering goes clockwise. There are only two nitrogen atoms. One on position 1 and the other at position 3
• In purines, the numbering starts differently — N9 is the nitrogen where the sugar attaches, and numbering goes anti clockwise around the fused rings.

This numbering system helps identify where bonds form and where substitutions or reactions happen (like where the sugar attaches to form a nucleotide).

Because purines have a two-ring structure (a six-membered ring fused to a five-membered ring). The nitrogens are at:
• N1, N3, N7, and N9(so four nitrogen’s but pyrimidines have two nitrogen’s)

In both cases, the sugar (ribose or deoxyribose) forms a β-N-glycosidic bond with the nitrogen on the base:
• N1 of pyrimidine
• N9 of purine

This linkage is what forms a nucleoside:
• Base + sugar = nucleoside
(e.g., adenine + ribose = adenosine)