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DNA = phosphate + deoxyribose sugar + A/T/C/G
o Contains two strands. The strands are antiparallel (opposite each other).
o 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:
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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’
BIOCHEM C785 Kaleys Comprehensive Study Guide final
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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 anew 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. Thisis 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 beginningof a gene. Each gene has its own promoter. Once bound, RNA
polymerase separates the DNA strands, providing the single‐ stranded template needed for
transcription.
BIOCHEM C785 Kaleys Comprehensive Study Guide final