How
Proteins are
Made
From DNA to RNA to Proteins
Chapter 10 Biology
RNA consists of a single strand of
nucleotides
 RNA nucleotides contain the 5 carbon
sugar ribose, rather than deoxyribose.
 RNA contains the nucleotide Uracil,
rather than thymine.
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Differences between
RNA & DNA
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Genes, in DNA, code for the proteins your
body will make.
These proteins are not directly made from
DNA, RNA has an important role.
DNA transfers instruction to RNA, through a
process called “Transcription”
Cells then read the instructions on the RNA,
using 2 other types of RNA, to assemble
amino acid sequences, making proteins. This
process is called “Translation”
Gene Expression
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mRNA: a form of RNA that carries instructions
for making proteins from a gene and delivers
those instructions to the site of translation.
tRNA: single strands of RNA that temporarily
carry a specific amino acid on one end.
rRNA: RNA molecules that are part of the
structure of ribosomes, the organelle which is
responsible for protein synthesis.
3 Types of RNA
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RNA polymerase is an enzyme that adds and
links complementary RNA nucleotides during
transcription.
RNA polymerase binds to promoter site, which
starts transcription.
RNA polymerase unwinds DNA strands.
RNA polymerase then begins adding
nucleotides as it reads the DNA strand.
Thymine is replaced with Uracil.
Continues until it reaches a stop signal.
http://www.youtube.com/watch?v=ztPkv7wc3y
U
Transcription-takes place
in the nucleus
Transcription-making mRNA
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mRNA leaves the nucleus and enters the cell’s
cytoplasm.
Ribosomes temporarily holds 1 mRNA and 2
tRNA.
Translation can begin when a tRNA carrying
the amino acid methionine (codon AUG) joins
the mRNA, and rRNA subunits.
tRNAs carrying specific amino acids coded for
on the mRNA, bind to the unit.
Peptide bonds form between the amino acids.
The process is continued until a stop codon is
reached
Translation
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http://www.youtube.com/watch?v=1PSwhTGF
Mxs
Codons-RNA
instructions
written as a series
of 3 nucleotide
sequences on
mRNA.
Anti-codons: a
3 nucleotide
sequence on a
tRNA that is
complementary
to an mRNA
codon.
Codons in mRNA
A few mRNA codons are
responsible for starting and
stopping translation.
AUG-start codon
UAG, UAA, UGA
-stop codons
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Cells express only a small percentage of the
genes they contain at any given moment.
The human genome has about 30,000 genes,
regulating gene expression on an “as needed”
basis. This conserves the cell’s energy.
This process occurs in both prokaryotes and
eukaryotes.
Gene Regulation and Structure
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E.coli has a well understood gene
regulation, in the breakdown of
lactose for energy.
1. The 3 lactose-metabolizing genes
are located next to each other.
 2. The on-off switch “turns on”
(transcription & translation)
when lactose is available and
“turns off” when lactose is not
available.
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Turning Protein Synthesis On/Off
in Prokaryotes
Lac Operon
Operator: The piece of DNA that overlaps the promoter
site and serves as the on-off switch.
 Operon: a group of genes that code for enzymes
involved in the same function, their promoter site,
and the operator that controls them all functioning
together.
 Repressor: A protein that binds to an operator and
physically blocks RNA polymerase from binding to
a promoter site.
 lac o.peron: The operon that controls the metabolism of
lactose.
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Eukaryotic Genes
Mutations are changes in the DNA
of a gene.
 Mutations in the body cells affect
the carrier.
 Mutations in gametes will be
passed to offspring.
 There are several types of
mutations possible.
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Mutations