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Gene Expression
How is the information in DNA used
to determine an organism’s
characteristics?
 An
organisms
trait’s are
determined by
proteins that are
built according to
the plans
specified in its
DNA.
What are Genes?
 Hold
information specifying how to
build particular proteins.
 Referring back to the gym socks what
part of the sock did the gene
represent?
 Genes
are the DNA-encoded
information that specifies particular
proteins; each gene is made of a
specific sequence of
____________???
 nucleotides
Transcribe and
Translate a Gene
 The
DNA that makes up the human
genome can be subdivided into
information bytes called genes. Each
gene encodes a unique protein that
performs a specialized function in the
cell. The human genome contains
more than 25,000 genes.
 Cells
use the two-step process of
transcription and translation to read
each gene and produce the string of
amino acids that makes up a protein.
The basic rules for translating a gene
into a protein are laid out in the
Universal Genetic Code.
How do you build
 It
a protein?
goes through two steps.
The first step is to undergo
TRANSCRIPTION and make
RNA!!!
Transcription
 In
st
1
step
the nucleolus the cells machinery
copies the gene sequence into
messenger RNA (mRNA), a molecule
that is similar to DNA. Like DNA,
mRNA has four-nucleotide bases-but
in mRNA, the base uracil (U) replaces
thymine (T).
Creating new strands
DNA:
 Complimentary:
 RNA

GGTATCGATTGG
CCATAGCTAACC
GGUAUCGAUUGG
DNA vs. RNA
DNA
 Double strand
 5-C sugar
deoxyribose
 Nitrogen bases:
ATCG
RNA
 Single strand
 5-C sugar ribose
 Nitrogen bases:
AUCG
 Uracil is
complementary to
adenine
RNA polymerase
 Binds
to a promoter
 Unwinds and breaks sequence
 Builds up sequence by pairing up each
nucleotide with its complementary
base
What is the Role of DNA in this
Process?
Step 1: RNA polymerase binds to
gene’s promoter
Step 2: The two DNA strands
unwind and separate
Step 3: Complementary RNA
nucleotides are added
Step 4
Step 5
Transcription

Transcription copies the DNA code of a
gene and converts it to messenger RNA (m
RNA). The m RNA will be used at the
ribosome to make polypeptides (proteins).
However all of the code contained in the m
RNA molecule is not needed to produce the
polypeptide. The sections of m RNA which
do not code for translation of polypeptide
are called introns.

As the m RNA readies itself to leave the
nucleus, enzymes cut out and remove the
introns. The remaining exons are spliced
back together again by a different enzyme.
This modified m RNA is what comes to the
ribosome to be translated into polypeptides.
RNA
3
TYPES:
messenger RNA (mRNA)
ribosomal RNA (rRNA)
transfer RNA (tRNA)
mRNA
 Holds
the information from DNA and
passes it on to create a protein
 It’s an RNA copy of a gene used as a
blueprint for a protein.
 When a cell needs a particular protein,
a specific mRNA is made.
rRNA
 Associates
with protein to form
the ribosome
tRNA
 Acts
as an interpreter molecule,
translating mRNA sequences into
amino acid sequences
Genetic Code
 After
transcription the genetic material
message is ready to be translated from
the language of RNA to the language
of proteins.
 The instructions for building a protein
are written as a series of 3 nucleotide
sequences called codons.
Translation:

nd
2
Step
The protein-making machinery, called the
ribosome, reads the mRNA sequence and
translates it into the amino acid sequence
of the protein. The ribosome starts at the
sequence AUG, then reads 3 nucleotides at
a time. Each 3-nucleotide codon specifies
a particular amino acid. The “stop”
codons (UAA, UAG, and UGA) tell the
ribosome that the protein is complete.
Translation
Transcribe and Translate a Gene.htm
Overview



DNA duplicates itself in replication.
DNA produces RNA in transcription.
RNA produces proteins in translation.

A, RNA, and Proteins

Protein builder
Transcribe a DNA
sequence into a protein
Protein
Extra Slides
Transcription

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Transcription is the process of creating RNA from DNA.
Transcription occurs in the cell's nucleus.
RNA polymerase is the protein molecule that reads the
DNA and creates the RNA intermediary.
Transcription requires: DNA, RNA polymerase,
ribonucleotides, and some ATP for energy.
Uracil (U) is substituted for thymine (T) in RNA.
Transcription initiation is the main point of regulation
of gene expression.