Molecular genetics Flashcards
Chromatin threads
- made up of histone proteins coiled arnd deoxyribonucleic acid (DNA)
How is DNA organised inside cell nucleus (each DNA molecule)
- consists of 2 anti-parallel strands, twisted arnd each other, double helix
- wrapped arnd histone proteins
- during cell div, chromatin threads coil tightly to form chromosome
Define DNA
- molecule that carries genetic info
- made up of nucleotides (basic unit of DNA)
- each DNA nucleotide made up of
1. a deoxyribose (sugar) molecule
2. phosphate group
3. a nitrogen-containing base
Nitrogen-containing base
- 4 types
- adenine (A)
- cytosine (C)
- guanine (G)
- thymine (T)
Polynucleotides
- formed when nucleotides join tgt by condensation
- DNA molecule made of 2 anti-parallel polynucleotide strands (double-helix)
- bases of both strand form tgt according to rule of base pairing
Rule of base pairing
- Adenine and thysine (A&T)
- Cytosine and guanine (C &G)
- complementary bases
- 1:1 ratio for A:T and G:C
Define gene
- segment of DNA
- specific sequence of nucleotides
- controls synthesis of specific polypeptide
Codon
- triplet code, 3 nucleotides forms an amino acid
genetic code states which amino acid each triplet code is for
What happens when nucleotide sequence is altered?
- known as gene mutation
- may or may not lead to change in protein product
Examples of gene mutation
- refers to change in genetic material of a gene
- e.g albinism, gene that cause absence/defect in melanin (enzyme that produces pigment)
- e.g. sickle-cell anaemia, mutation in gene that causes protein product to differ from normal protein by 1 amino acid, RBC become sickle shaped
How are proteins made?
- transcription
- translation
Transcription (brief overview)
- DNA separate out, 1 template DNA (Strand), 1 non-template DNA
- occurs when DNA template transcribed into mRNA
- occurs in nucleus of cell
- DNA triplet code converted into mRNA codons
Translation (brief overview)
- mRNA molecule translated into polypeptides
- occurs in cytoplasm of cell
DNA vs RNA (sugar unit)
- DNA: deoxyribose
- RNA: ribose
DNA vs RNA (nitrogenous bases)
- DNA: Adensine (A), Thymine (T), Guanine (G), Cytosine (C)
- RNA: Uracil (U) instead of Thymine (T), rest same
DNA vs RNA (ratio of nitrogenous bases)
- DNA: A:T=1:1, G:C=1:1 (becos double helix, each base has a partner)
- RNA: no fixed ratio (single-stranded, each base no partner)
DNA vs RNA (size and solubility)
- DNA: large, insoluble molecule (cannot leave nucleus)
- RNA: small, soluble molecule (can leave nucleus)
DNA vs RNA (temporary vs permanent)
- DNA: permanent molecule in nucleus
- RNA: temporary molecule, made when needed
Translation (biological molecules involved)
- Amino acids: 20 types
- Transfer RNA molecules: tRNA, each has aa attached, aa attached depends on tRNA’s anticodon
- Ribosomes: help make polypeptides from mRNA
- mRNA molecules
What happens during transcription? (4)
- Gene unzips
- DNA template formed in nucleus
- mRNA formed, complementary copy which contains uracil instead of thymine
- mRNA exits out of nucleus and enters cytoplasm
What happens during translation? (6)
- mRNA attaches to ribosome
- tRNA with anticodon complementary to mRNA attaches to ribosome as ribosome moves along mRNA strand
- amino acids attached to tRNA forms peptide bonds with each other
- tRNA gets released, a new one fits into ribosome
- amino acids continually attached until ribosome reaches stop codon on mRNA, ribosome leaves mRNA
- complete polypeptide produced (chain of aa)
