Unit 7
• RNA, Protein Synthesis &
Gene Expression
Chapter 10-2, 10-3
(page 190 – 197)
Chapter 11
(pg 203 – 214)

Unit 7
 Lecture 1
 Topics:
 DNA vs RNA
 Covers:
 Chapter 10-2
 Pages 190 - 191
RNA Introduction

RNA (Ribonucleic Acid) is another type of
nucleic acid.
 Nucleic Acid – Organic compound, polymer
made up of monomers known as nucleotides

RNA uses the genetic information stored in DNA
to create proteins. Remember:
 DNA stores genes and is kept in the
nucleus
 Gene – code for a protein
 Ribosomes (outside nucleus) make
proteins

Protein synthesis – process where a cell makes a
protein
Protein Review

Proteins are polymers made up of monomers known as amino acids
 A chain of many amino acids is known as a polypeptide


Once a polypeptide is folded/coiled into its final shape, then it
is called a protein
The shape (and function) of each protein is very different

A gene codes for the order of amino acids in a protein
 The sequence of amino acids determines how the polypeptide
will eventually coil/fold on itself (determines final shape of protein)

There are twenty different kinds of amino acids
 Each amino acid is coded for by a specific combination of nucleotides
Protein Review
Comparison of
DNA and RNA
Nucleotide Components
DNA
RNA
Sugar
Nitrogen
Base
Deoxyribose
Adenine
Guanine
Cytosine
Thymine
Ribose
Adenine
Guanine
Cytosine
Uracil (a
pyrimidine)
Function
Structure
Varieties
Stores genetic
information
(genes)
Double helix
(two strands
Only one
type
connected in
center of helix)
Uses genetic Single helix
information
to make
proteins
(single strand
of nucleotides)
Remember: a gene is a code for a protein
Three
types
- rRNA
- mRNA
- tRNA
Comparison of
Three types of RNA
 rRNA (Ribosomal RNA)
 Makes up part of a ribosome
 Remember:
 Ribosomes are made up of RNA and proteins
 Ribosomes are organelles that make proteins
Comparison of
Three types of RNA

mRNA (Messenger RNA)
 Brings the genetic message from
DNA to a ribosome
 DNA gene (protein message)
copied into mRNA
Comparison of
Three types of RNA

tRNA (Transfer RNA)
 Used during protein synthesis
 Transfers amino acids to their proper
place in the amino acid chain
END OF LECTURE 1
Unit 7
 Lecture 2
 Topic:
 Introduction to
Protein Synthesis
 Covers:
 Chapter 10-2 and 10-3
 Pages 191 – 195
Protein Synthesis

DNA (Chromosomes) store genetic information. Each strand of
DNA stores hundreds of genes

The order (sequence) of nucleotides in the gene codes for the
order of amino acids in the protein
 A mutation that occurs in a gene could affect the protein code
 Mutation – change in the order of nucleotides (DNA or RNA)
 A gene mutation could change the order of amino acids in
the protein or could prevent the protein from being made
Protein Synthesis

To make a protein:
1. A copy of a gene is made (DNA copied into mRNA)
 This mRNA template serves as the code for the protein,
instructions for how to make the protein
2. mRNA carries the protein code from the nucleus to a ribosome
 Protein synthesis takes place outside the nucleus by a:
 Bound ribosome – makes proteins to leave the cell
 Free ribosome – makes proteins to be used in the cell
3. Ribosome translates mRNA sequence into an amino acid sequence
4. The chain of amino acids will fold into final protein product
Protein Synthesis
The Genetic Code

The order of nucleotides in the mRNA template codes for the order
of amino acids in the protein chain

Ribosome translates the information from mRNA into amino acids

mRNA is made up of nucleotides; Proteins made up of amino acids
Protein Synthesis
The Genetic Code

A combination of three nucleotides codes
for one amino acid
 CODON – Three nucleotide sequence
that codes for an amino acid



64 codons, but there are only 20
amino acids
Some amino acids have more than one
codons
Important codons: START (AUG), and
STOP (UAA, UAG, UGA)
•
Phenylalanine (Phe),
Leucine (Leu),
Isoleucine (Ile),
Methionine (Met),
Valine (Val), Serine
(Ser), Proline (Pro),
Threonine (Thr),
Alanine (Ala),
Tyrosine (Tyr),
Histidine (His),
Glutamine (Gln),
Asparagine (Asn),
Lysine (Lys),
Aspartic acid (Asp),
Glutamic acid (Glu),
Cysteine (Cys),
Tryptophan (Trp),
Arginine (Arg),
Glycine (Gly)
Protein Synthesis
The Genetic Code

Each amino acid is carried through the
cell and to the ribosome by a specific tRNA (Transfer RNA)

tRNA is shaped like a “t”
 One end (end of chain) bonds to a specific amino acid
 Opposite end (bottom loop end) attaches to mRNA
 This section is known as the ANTICODON
 Anticodon is complementary to each mRNA codon
 Example: Amino Acid – Serine
 CODON – “AGU”
 Serine transferred to amino acid chain by tRNA
with the ANTICODON – UCA
End of Lecture 2
Unit 7
 Lecture 3
 Topic:
 Protein Synthesis
 Transcription
 Translation
 Covers:
 Chapter 10-3
 Pages 193 – 196
Protein Synthesis
•
Protein Synthesis is a two part process
1. Transcription
•
•
This is when a gene is transcribed (copied)
DNA gene copied into mRNA
2. Translation
•
•
•
This is when the genetic code is translated
into a protein
mRNA message translated into amino acids
Amino acid chain shaped into final protein product
Transcription
1. RNA Polymerase (an enzyme) binds to a gene on the DNA
 RNA polymerase separates the two strands of DNA
Transcription
2. One of the separated DNA strands is copied
 This DNA strand is known as the TEMPLATE
3. RNA Polymerase moves along the DNA template and adds the
complementary RNA nucleotide
DNA
RNA
Complementary Base
Guanine Cytosine
Cytosine Guanine
Thymine Adenine
Adenine URACIL
Transcription
4. RNA polymerase continues until it reaches the end of the gene
5. RNA Polymerase releases DNA and gene copy (mRNA template)
 DNA strands bond back together, goes back to double helix
 mRNA template will leave the nucleus and go to a ribosome
Transcription
Translation
•
Once the mRNA reaches a ribosome, the
genetic message will be translated into a protein
• The ribosome will scan down the mRNA strand, translating
each codon into an amino acid
• tRNA transfers each amino acid into the proper place based on
the mRNA message
• Remember:
• A CODON (in mRNA) codes for one amino acid
• Each amino acid is transferred in place by tRNA
• ANTICODON – in tRNA, complementary to codon
• PROTEIN – polymer made up of monomers of amino acids
Translation
Translation
1. mRNA leaves nucleus and goes to a ribosome to begin protein
synthesis
2. Ribosome will attach to the end of the mRNA. The ribosome will
begin to move down the mRNA template.


tRNA will also begin to transport amino acids (floating in cytosol)
to ribosome
Each amino acid is carried by a different tRNA
Translation
3. The ribosome will "scan" down the mRNA template until the
ribosome reaches the start codon of mRNA.

When the ribosome reaches the start codon (AUG), the
ribosome will stop moving.

tRNA with the anticodon (UAC) can bond with the start codon.
 tRNA adds first amino acid of the chain: methionine (MET)
Translation
4. After the first amino acid is attached, the ribosome will move down
to the next codon. The next codon will be translated.
 tRNA will attach the amino acid
 MET and the second amino acid will bond together
 Peptide bonds hold the amino acids together
 Peptide Bond – covalent bond between amino acids
5. Ribosome will continue to move down the mRNA strand, stopping at
each codon.
 tRNA attaches to each codon and adds the correct amino acid.
 The amino acids are attached in a chain by peptide bonds.
Translation
6. When the ribosome reaches the “STOP” codon, no more amino
acids are added
 "STOP" codons (UAA, UAG, UGA) don’t code for an amino acid
7. Long chain of amino acids is released
 Long chain of amino acids – Polypeptide
8. Ribosome separates from the mRNA strand.
9. Polypeptide will coil/fold into its final shape, it will then be known
as a protein
End of Lecture 3
Unit 7
 Lecture 4
 Topic:
 Cell Differentiation
 Gene Expression
 Covers:
 Chapter 11
 Page 209
Cell Differentiation
 Only certain sections of the DNA molecule code for a gene
 A gene is a section of DNA that codes for a protein
 The longer the strand of DNA, the more genes it can store
 Non-coding Region – Sections of DNA that do not code for
proteins
Cell Differentiation
 In a multicellular organism, every cell in the body has the same DNA
 Every cell in the body came from one cell – a fertilized egg
(embryo)
 Embryo divides numerous times to add new body cells
 Uses process of mitosis to add new body cells (Somatic Cells)
 This means that every cell in our body has the same genes
 In humans, each somatic cell is a diploid cell and has 46
chromosomes
Cell Differentiation
 Every cell in a multicellular organism contains all of the organism’s
genes
 But, each cell does not need to use every gene to function
properly.
 Differentiated (specialized) cells only use the genes necessary for
that cell type to function
 Only makes the necessary proteins for that cell type
 Cells can regulate which proteins they make by controlling which
genes are activated and used to make proteins.
Gene Expression
 GENE EXPRESSION - activation of a gene
that results in the formation of a protein.
 A gene is expressed when it is copied into RNA
 Control of gene expression is very important in embryo
development and as cells are becoming specialized
 Before cells become specialized, they are known as Stem Cells
 Stem cells activate certain genes & begin to become specialized
 This causes the cell to change its shape to take on its final
specialized form and function
 Remember: Our body is made up of over 200 different types of
cells! Each cell/tissue type has its own unique form & function
End of Lecture 4