Biology 12: Protein Synthesis
Mr. Kruger
DNA & Protein Synthesis
One of the single most unifying characteristics of all life is the presence and function of
DNA. . . It is therefore very important for us to understand the structure and function of
DNA. DNA is part of a group of molecules called nucleic acids that are essential in
carrying and expressing the genetic information of cells.
1. Nucleic Acids:
Function:


Directs and controls all cell activities
Contains all of the genetic information necessary to make one complete
organism of very exact specifications
Biology 12: Protein Synthesis
Mr. Kruger
Types of Nucleic Acids:
 Deoxyribonucleic Acid: DNA
(DNA is the largest known molecule)

Ribonucleic Acid: RNA
Structure (see pg. 142, fig 7-7):
 nucleic acids are composed of units called NUCLEOTIDES, which are
composed of three sub-molecules:

Pentose sugar (either ribose or deoxyribose)

Phosphate

Nitrogen base: two groups (purine and pyrimidine)
P
a.) Purines: Adenine and Guanine
Two rings
Found in both DNA and RNA
b.)Pyrimidines: Cytosine, Thymine, and Uracil
One ring
Cytosine is in both DNA and RNA
*Uracil is in RNA only
*Thymine is in DNA only
2. Structure of DNA (see pg.144 fig. 7-11)
 DNA is composed of two complimentary strands of nucleotides.
 The complimentary pairings are always:
 Adenine with Thymine (A-T or T-A)
 Cytosine with Guanine (C-G or G-C)
 This bonding of bases is called Complementary Base Pairing.
 The double strand is held in place by hydrogen bonds between the bases.
3. Levels of DNA Structure:


Primary structure: the type and order of the nitrogen base pairs
(the “ genetic code”)
Secondary structure: the formation of a double helix takes place due to hydrogen
bonding within the molecule
Biology 12: Protein Synthesis
Mr. Kruger
4. Functions of DNA

DNA controls the actions of a cell. DNA directs the production of specific
proteins, and, therefore, DNA indirectly (by making proteins) controls all
of the functioning of all living things.

DNA stores the hereditary information to make an individual

DNA has the ability to change (mutate). This allows for new
characteristics and abilities to appear which may help an individual to
survive and reproduce
EVOLUTION

Replication: DNA has the ability to make copies of itself
5. DNA Replication…. Recap.

DNA replication is called ‘semi-conservative’.

Semi-conservative replication is the process in which the original strands of DNA
remain intact and act as templates for the synthesis of duplicate strands of DNA.

One copy of a DNA molecule will split apart to make two complete copies of
itself. Each new DNA molecule is made up of half of the old molecule and half of
a new molecule.
Steps involved in DNA replication:
*** SEE PAGE 145 FIGURE 7-12***
1. UNZIPPING: The DNA molecule ‘Unzips’ as the hydrogen bonds between the
base pairs are broken. The enzyme HELICASE causes this unzipping to occur.
2. COMPLEMENTARY BASE PAIRING: Complementary nucleotides move into
position to bond with the complementary bases on the DNA strand
3. JOINING OF ADJACENT NUCLEOTIDES: The nucleotides join together via
sugars and phosphates to form a new backbone. This process occurs due to the
enzyme DNA POLYMERASE.
4. This process continues along the primary strands until we have 2 IDENTICAL
STRANDS of DNA molecules (assuming there have been no errors made).
Biology 12: Protein Synthesis
Mr. Kruger
Proteins:
Slightly different proteins can often perform the same function.
These different proteins can take on slightly different appearances.
Example: Skin color
Eye color
This difference in appearance of proteins results in the Diversity of life on Earth.
Proteins can have many different Functions:
a) Structural Proteins: Make up body parts.
b) Enzymes: Are proteins that regulate the speed of chemical reactions.
c) Transport Proteins: Carry substances throughout the body.
Example: Hemoglobin carries oxygen
d) Protection Proteins: Protect the body from foreign invasion
Example: Antibodies
e) Hormone Proteins: Chemical messengers
There are 20-22 common amino acids in living organisms.
The sequence of these amino acids result in the final protein
Changing even one amino acid in a sequence can result in a mutation of the entire
protein.
Most mutations make the protein useless which can be fatal in living things.
Example of minor mutations: Diabetes (no insulin)
Sickle-cell anemia (can not carry
oxygen)
Hemophilia (blood can’t clot)
A small number of mutations in proteins actually improve the chances of survival for an
organism. These positive mutations allow to increase the Diversity of Life.
DNA VS RNA
Both are nucleic acids mad up of nucleotides.
DNA (Deoxyribonucleic Acid)
Sugar is deoxyribose (5 carbon)
Double stranded
Shape : double helix
Found only in the nucleus
Bases: A – Adenine
C– Cytosine
G – Guanine
T – Thymine
DNA : only one type
RNA (Ribonucleic Acid)
Sugar is ribose (5 carbon)
Single stranded
Strand; no particular shape
Found in nucleus and cytoplasm.
Bases: A, C, G, but not T Thymine is
replaced by U – Uracil
Types of RNA:
mRNA- Messenger RNA
tRNA –Transfer RNA
rRNA – Ribosomal RNA
Biology 12: Protein Synthesis
Mr. Kruger
Protein Synthesis
Introduction
*DNA replication produces and identical DNA strand.
*Protein synthesis uses DNA to produce proteins.
Do not confuse these 2 processes!!!!!!
DNA is the master copy (or template) containing instructions for the production
of proteins. (structural and functional)
Proteins are put together in the cytoplasm, but DNA never leaves the nucleus. A
copy of the DNA must be made. This copy is called messenger RNA (mRNA). Only
genes for required proteins are copied into mRNA. The process of making mRNA is
called transcription.
mRNA travels into the cytoplasm where it is translated into proteins.
DNA--------------------> mRNA-------------------------> Protein
transcription
translation
Biology 12: Protein Synthesis
Mr. Kruger
The nitrogenous bases in DNA contain the instructions for making proteins. Every 3 bases
in a DNA strand code for one amino acid. Many amino acids make up a protein.
Each 3 base set is called a codon.
Biology 12: Protein Synthesis
Mr. Kruger
There are 64 possible combinations:
However, we only have about 20 amino acids, therefore most amino acids have
more than 1 codon. Often the codons only differ in the last base.
Example: CAA & CAG
Both codons are for the A.A. glutamine.
Duplicate codons may be a way of protecting/reducing the effects of mutations.
The duplication of codons is called degeneracy.
The genetic code is basically “Universal” the same codons stand for the same A.A.
in all living things. This suggests that all living things came from a common ancestor.
Transcription (Trans = across, cription = to write)

The coded message of a gene on DNA has specific instructions on how to
make each particular protein that our bodies need.
Biology 12: Protein Synthesis

Mr. Kruger
The instructions from a gene are copied from DNA to messenger RNA
(mRNA) in the nucleus.

Then, the mRNA moves through pores in the nuclear membrane into the
cytoplasm where the proteins are made.

The process of making mRNA is called transcription
DNA
mRNA
A
U
T
A
C
G
G
C
Translation

The mRNA code is made up of groups of three nucleotide bases known as
codons. Each codon codes for a specific amino acid.
Eg. AGC = Serine
Eg. AGG = Arginine
Eg. UGC = Cysteine

The written code (codons) on mRNA is ‘translated’ into a specific amino acid
sequence by ribosomes in the cytoplasm.

This is carried out with the help of relatively small transfer RNA (tRNA)
molecules.

A tRNA molecule is a small piece of RNA that has a specific amino acid
attached to it.
The tRNA also has a special sequence of 3 nucleotide bases known as an anticodon.
There is at least one type of tRNA for each of the 20 amino acids.

As the correct amino acids are brought to the ribosome by the tRNAs, they are
joined together via dehydration synthesis to form the protein that the original
DNA coded for.
Biology 12: Protein Synthesis
Mr. Kruger
IF the DNA strand is TTATGCTCCTAA
1. What is the sequence of codes on the complementary DNA strand?
AAT/ACG/AGG/ATT
2. What are the codons on the mRNA strand.
AAU/ACG/AGG/AUU
3. What is the sequence of amino acids.
Asparagine/threonine/Arginine/Isoleucine
Biology 12: Protein Synthesis
Mr. Kruger
Question: What if something goes wrong during translation?
Answer: Mutation – A change in the nucleotide sequence of DNA
A factor that increases the chance of a mutation is called a mutagen.
Environmental Mutagens
1) Chemical – food additives
-- hallucinogenic drugs (LSD)
-- pesticides/fertilizers
-- industrial chemicals
2)
Radiation –(non visible short wavelength from electromagnetic
spectrum)
-- The greater the exposure the greater the risk.
Suspected mutagens are tested on bacteria such as Fruit flies, and then mammals
(rats, mice). If mutations (such as cancer) develop, the government restricts its
use.
Mutagens that lead to an increased chance of cancer are called carcinogens.
There are two types of mutation:
a) Chromosomal mutations: a mutation of all or part of a chromosome.
Example: non-disjunction where there are extra or missing
chromosomes. Down syndrome is an example of non-disjunction as
it occurs when a person has one extra 21st chromosome.
Example: crossing over where one part of a chromosome changes
places with another. This can cause extra pieces, missing pieces, or
the exchange of pieces of chromosomes.
b) Gene mutations: a mutation that occurs within a gene at some point
along a chromosome.
There are 3 types:
1. Deletion: when one nucleotide base is left out. This will
change the entire amino acid sequence of the protein.
Serious.
2. Addition: when one extra base is added. This will also
change the entire amino acid sequence of the protein.
Serious.
3. Substitution: when single bases or short pieces are replaced
with one another. An example is Sickle-Cell Anemia, where a
single nucleotide base is switched and a glutamate is replaced
by a valine. Serious, but not as serious as the 1st two.
Biology 12: Protein Synthesis
Mr. Kruger
Genetic Engineering: artificial manipulation of the genetic material (DNA) of any
species for a specific purpose
1) Cloning: every cell in an organisms’ body contains the full set of genes
to make a new organism. Cloning is using one cell from an organism to
make a whole new organism.
2) Recombinant DNA: modifying the DNA of some organism
a) gene displacing: introduce new genes
b) gene modification: repairing a gene
c) gene transformation: inserting genes from a different species to give
a new function
Uses of Genetic Engineering
a) Agriculture
i)
ii)
iii)
iv)
v)
vi)
Disease resistant crops
Add nutrients
Increase yield
Grow faster and use less water
Less fertilizer needed, can grow in colder areas
Superior animals
b) Medicine
i)
ii)
new medicines (ie: insulin, antibiotics, hormones)
cures for disease (ie: cancer)
c) Industry: Manufacture chemicals (ie: aspartamine, bacteria that eat
oil, mining)
d) Gene Therapy: Cystic fibrosis (fix the gene)
e) Future: Designer genes to make genes to do whatever we want