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Protein
Synthesis
RNA
 Ribonucleic
acid(RNA) consists of a single
strand of nucleotides instead of the 2
strands found in DNA
 RNA nucleotides contain ribose isntead of
deoxyribose. Ribose has an OH on the 2nd
carbon
 RNA uses the nitrogenous base uracil
instead of thymine. Uracil attaches to
adenine
Protein Synthesis
 Step
1 – Transcription is the transfer of the
information from DNA to RNA
 Step 2- Translation is the process of reading
the information on DNA and converting it into
the amino acid sequences of the protein
 The specific sequence of genes (bases) on
DNA directly determine the sequence of RNA,
and therefore the types of proteins made
Transcription
 Transcription
is the synthesis of messenger
RNA (mRNA) from DNA
 Occurs in the cytoplasm in prokaryotes
and the nucleus in eukaryotes
 Three key steps: Initiation, Elongation,
Termination
Transcription
 Initiation



Promoter- a specific sequence of DNA that
signals the start of transcription, like the
starting line in a race
RNA polymerase finds to the promoter on
DNA
RNA polymerase then separates the 2 DNA
strands by breaking the hydrogen bonds
Transcription
 Elongation



As RNA polymerase moves along DNA, it
untwists the double helix and separates the
strands
RNA polymerase then adds nucleotides to
the 3’ end of mRNA
Follows the base-pair ruling, but now pairing
U with A
Transcription
 Termination



Termination signal- sequence of bases in
DNA that tell RNA polymerase to stop
transcription
Most common terminal signal is AATAAAA
RNA polymerase is released from DNA and
DNA will re-anneal
RNA Modifications
 In
eukaryotes, mRNA is modified before
it’s sent out of the nucleus
 2 major types of modifications

Alterations of mRNA ends and RNA splicing
RNA Modifications
 5’
end received a guanine cap
 3’ end received a poly-A tail, 50-250
adenine nucleotides
 These help protect mRNA from breaking
down
RNA Modifications
 Genes
have stretches of nucleotides that
don’t code for anything, called “junk
DNA” (pre-mature mRNA)
 These regions are called introns or
intervening sequences
 Coding regions = exons
 An enzyme called a spliceosome removes
the introns and join the exons together
(mature mRNA)
Translation
 The
building of a polypeptide (protein)
from mRNA
 Uses transfer RNA (tRNA) to help
 Occurs in the cytoplasm on the ribosome
Translation
 tRNA


3
– cloverleaf shape
Contains anticodon – triplet of bases
complementary to the bases (codon) on mRNA
Carries corresponding amino acid on the other
end that can detach
bases needed per 1 amino acid
 Codons are 3 nucleotide sequences for an
amino acid, found on mRNA
 The codons bind to the anticodons on tRNA,
which will then bring the corresponding amino
acid to form a protein
Translation
 Ribosomes


Made up of 2 subunits, large and small
made of ribosomal RNA (rRNA)
Have special binding sites
P
site holds tRNA with amino acid chain
 A site hold the next tRNA
Translation
3
stages: Initiation, Elongation, Termination
 Initiation





mRNA and tRNA join
Anticodon + complementary codon
mRNA start codon is AUG
tRNA is UAC and brings the “start” amino
acid methianine
Large and small subunits join, forming a
functional ribosome around the RNA
Translation
 Elongation

Amino acids are added one by one by the
following process
 mRNA
codon binds with anticodon on tRNA
 Peptide bond is formed between the new
amino acid and the last one
 tRNA moves over from A site to P site
Translation
 Termination


Elongation continues until a stop codon is
reached (UAA, UAG, UGA)
Polypeptide (protein) is released from
ribosome and ribosome falls apart into the 2
subunits
Gene Regulation
 Mutations-
change in the DNA (gene)
and only passed onto offspring if in the sex
cells
Gene Regulation
 Gene
rearrangements- mutation that
moves an entire set (of bases) to a new
spot


Transposition- gene moves
Chromosomal- chromosome rearranges
Gene Regulation
 Gene
gene

alteration- mutations that change a
Point mutation- a single base is changed
 Base
pair substitution- changes one base for
another
 Silent- base pair substitution that gives the same
amino acid, allowing for the protein to form
 Insertion- bases are added
 Deletion- bases are deleted
 Frameshift- an insertion or deletion that alters the
codon reading, always occurs with
insertion/deletions
Prokaryotic Gene Regulation
 Prokaryotes
only have ~2,000 genes
 The operator is the on/off switch
 The operon is a set of genes that code for
enzymes involved in the same function
 RNA polymerase attached to DNA at the
promoter and begins to transcribe
 It will continue until it reaches the
repressor, a protein that binds the
operator and blocks RNA polymerase
Eukaryotic Gene Regulation
 Eukaryotes
have 30,000 genes and the
process is more complicated
 They have a promoter, enhancer, and
activator
 The enhancer is a sequence of DNA that
can be bound by transcription factors (TF,
a protein that controls transcription)
Eukaryotic Gene Regulation
 The
activator attaches to the enhancer
and causes a loop to form bringing the
enhancer close to the promoter by being
in contact with the TF
 RNA polymerase attaches to the
promoter and beings transcription