Molecular biology notes, including DNA, RNA, protein synthesis, enzymes, cellular respiration, photosynthesis, properties of water, biological molecules (lipids, fats, etc) and more. Includes diagrams as well.
DNA structure
➔ Antiparallel strands + double helix
➔ Nitrogenous bases:
◆ Adenine + Thymine -- double bond
◆ Cytosine + Guanine -- triple bond
◆ complementary base pairing
➔ nucleic acids (DNA + RNA) are polymers made
of nucleotides
➔ Hydrogen bonds - dotted
Strong covalent bonds - lines
➔ S - deoxyribose sugar
P - phosphate group
B - nitrogenous base
➔ sugar-phosphate backbone
Chromosomes
- Structures containing genetic info
- DNA strands super-coiled around histone protein
- Supercoiling - organise for cell replication + makes smaller
- 46 in each cell, 23 pair in each cell
- 92 sister chromatids (one of two similar copied strands)
- 1- 22: autosomal chromosomes/autosomes
- 23: sex chromosomes
- XX for women, XY for men
, - Each chromosome has gene loci/sites where genes are found
Replication
- Helicase: enzyme that zips down/unwinds flattened DNA strand, breaks hydrogen bonds
- Polymerase: adds free nucleotides / links nucleotides together to form new strand
- works in one direction
- Semi-conservative replication
- Conservation of the complementary base pairing
- Conservation of the genetic code
RNA - ribonucleic acid
➔ Compared to DNA: only one strand, base composition is different, type of pentose
(structure) is also different (OH in RNA vs H in DNA)
➔ Replace T with Uracil -- ACG → TGC → UGC
➔ Messenger mRNA carries nucleotide to ribosome
➔ Transfer tRNA picks up amino acid in cytoplasm + carries them to ribosome
➔ Ribosomal rRNA found in ribosome, joins mRNA + tRNA; forms protein with codons
Protein Synthesis
- triplet code of nitrogenous bases codes on mRNA for each amino acid
- mRNA determines amino acid sequence of polypeptides (length of chain, which amino
acids + their positions) according to genetic code in DNA
Transcription - synthesis of mRNA copied from DNA base sequences by polymerase
1. part of DNA is opened by breaking H-bonds using RNA polymerase
2. RNA polymerase adds mRNA nucleotides to create strand of mRNA (messenger RNA)
3. mRNA nucleotides (codons) complementary base pair with DNA nucleotides, with Uracil
replacing Thymine. Codons are made of three nitrogenous bases coding for a specific
amino acid.
4. completed strand of mRNA moves out of nucleus and into cytoplasm, where it attaches to a
ribosome
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