Biochemistry: Mod 1
• DNA = phosphate + deoxyribose sugar + A/T/C/G
o Contains two strands. The strands are antiparallel (opposite each other).
o
... [Show More] 5’ → 3’
3’ ← 5’
• RNA = phosphate + ribose sugar + A/U/C/G
o Single strand, can fold back onto itself and form pairs between itself (stem‐loop).
• Each nucleic acid is made up of polymers (many monomers) that are called nucleotides.
o Nucleotides contain one or more phosphates, a five‐carbon sugar, and a nitrogen base.
o Nucleotides are always made in the 5’ to 3’ direction.
o 5 is always the beginning of the strand, 3 is the end where nucleotides are added.
• DNA organization: DNA is wrapped around proteins called histones → nucleosome → chromatin fiber→
chromosomes
• Steps to the central dogma:
o Coding DNA → template DNA → mRNA → tRNA (amino acid)
o DNA → transcribed to mRNA → translated to protein
o Each step is complementary (opposite) to the previous step, but if you skip a step it will be identical to
the previous step.
o Example
▪ 1. Coding DNA strand 5’ AAA TTT GGG CCC 3’
▪ 2. Template DNA strand 3’ TTT AAA CCC GGG 5’
▪ 3. mRNA 5’ AAA UUU GGG CCC 3’
▪ 4. tRNA Lys Phe Gly Pro
• Pairing:
o DNA: A → T
o RNA: A → U
• DNA replication:
o Because DNA is a double helix, one strand can be separated and serve as a template for synthesis of a
new strand.
o Semi‐conservative: each copy of DNA contains a template strand and a new strand.
o Steps of replication:
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o 1. The DNA must be separated, creating a replication fork. This is done by helicase.
o 2. Primase attaches an RNA primer, where the replication is to start.
o 3. DNA polymerase adds bases to the remaining of the strand until it reaches a stop codon. This
is done in fragments, called okazaki fragments.
• If an error is detected, it removes the nucleotides and replaces them with correct ones,
known as exonuclease.
o Exonuclease removes all of the RNA primers, and DNA polymerase fills in those gaps.
o DNA ligase seals the two strands forming a double helix.
• DNA → transcribed → mRNA → translated → protein
• Transcription occurs in the nucleus:
o Initiation: RNA polymerase binds to a sequence of DNA called the promoter, found near the beginning
of a gene. Each gene has its own promoter. Once bound, RNA polymerase separates the DNA strands,
providing the single‐stranded template needed for transcrip..............................................................CONTINUED [Show Less]