Download Carrying Information in DNA

Biology
HS/Science
Unit: 07 Lesson: 01
Carrying
DNA
Information in
One Gene Corresponds to One Polypeptide
Hypothesis
The information required to make an enzyme is
encoded as a gene in the DNA of the organism.
Historically, scientists believed that, in general, one
gene corresponds to one polypeptide.
The gene is a section of DNA that determines the
amino acid sequence of a polypeptide.
Beginning in 1957, scientists showed that some
genetic variations in proteins, such as sickle cell
hemoglobin, could be due to differences in only a
single polypeptide chain in a multimeric protein (a
protein formed from two or more, same or different,
polypeptide chains). They showed this through the
use of protein fingerprinting. This led scientists to
the “one gene-one polypeptide” hypothesis.
However, recent research has led scientists to
believe that genes can actually correspond to more
than one polypeptide.
A gene codes for a polypeptide, and several
polypeptides may be required for a functional
protein or enzyme.
Amino Acids Link Together to Form
Polypeptides
Twenty-two amino acids are naturally incorporated
into polypeptides and called proteinogenic or
natural amino acids.
Of these, 20 are encoded by the universal genetic
code.
Amino acids are molecules containing an amine
group, a carboxyl group, a central Carbon atom, a
Hydrogen atom, and a side-chain that varies
between different amino acids The key elements of
an amino acid are carbon, hydrogen, oxygen, and
nitrogen.
Amino acids are the structural units that make up
proteins.
They join together to form short polymer chains
called peptides or longer chains called either
polypeptides or proteins.
These polymers are linear and unbranched, with
each amino acid within the chain attached to two
neighboring amino acids.
©2012, TESCCC
05/08/13
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Biology
HS/Science
Unit: 07 Lesson: 01
DNA Triplets Code for One Amino Acid
The genetic code is made up of 64 triplets of
nucleotides.
Each triplet is called a codon.
Aside from three exceptions, each codon encodes
for one of the 20 amino acids used when proteins
are synthesized.
This means the code is redundant because most of
the amino acids are encoded by more than one
codon (triplet).
The codon AUG is responsible for signaling the start
of translation.
The genetic code can be expressed as RNA or DNA
codons.
The genetic code is almost universal. The
components that make up the genetic code are
common to all organisms.
TTT Phe
TCT Ser TAT Tyr
TGT Cys
TTC Phe
TCC Ser TAC Tyr
TGC Cys
TTA Leu
TCA Ser TAA STOP TGA STOP
TTG Leu
TCG Ser TAG STOP TGG Trp
CTT Leu
CCT Pro CAT His
CGT Arg
CTC Leu
CCC Pro CAC His
CGC Arg
CTA Leu
CCA Pro CAA Gln
CGA Arg
CTG Leu
CCG Pro CAG Gln
CGG Arg
ATT Ile
ACT Thr AAT Asn
AGT Ser
ATC Ile
ACC Thr AAC Asn
AGC Ser
ATA Ile
ACA Thr AAA Lys
AGA Arg
ATG Met* ACG Thr AAG Lys
AGG Arg
GTT Val
GCT Ala
GAT Asp
GGT Gly
GTC Val
GCC Ala
GAC Asp
GGC Gly
GTA Val
GCA Ala
GAA Glu
GGA Gly
GTG Val
GCG Ala
GAG Glu
GGG Gly
In most of the genes in animals, plants, and
microorganisms, START and STOP signals are
coded from the same codons and amino acids.
Although, a few exceptions have been noted, most
exceptions assign one or two of the three STOP
codons to an amino acid instead.
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05/08/13
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Biology
HS/Science
Unit: 07 Lesson: 01
How Information for Specifying the Traits of an Organism is Carried in the DNA
•
Deoxyribonucleic acid (DNA) is a nucleic acid made of nucleotides. Each nucleotide consists of a
sugar-phosphate backbone and one of the four nitrogenous bases (adenine, thymine, cytosine, and
guanine). (Look back at the Handout: The Structure of DNA for a visual.) DNA has the genetic
instructions that are used in the development and functioning of all organisms.
•
Genes are the DNA segments that carry genetic instructions for life. However, other DNA sequences
also have structural purposes or are involved in regulating the use of genetic information.
•
The sequence of the nitrogenous bases along the strand of DNA encodes the genetic information within
the DNA strand.
•
The code within DNA is a series of codons (triplets), which encodes for specific amino acids. Amino
acids then link together to form proteins.
•
The code can be read through a process called transcription. During this process, stretches of DNA
are copied to create RNA.
•
Chromosomes are the structures within cells that DNA is organized into.
•
During cell division, DNA replication occurs. DNA replication creates a full new set of chromosomes.
This allows each cell to have its own complete set of chromosomes.
•
In eukaryotic organisms, such as animals, plants, fungi, and protists, DNA is stored inside the cell’s
nucleus. In addition, some DNA may be stored in other organelles such as mitochondria or
chloroplasts.
•
In prokaryotic organisms, such as bacteria and archaea or archaeans, the DNA is stored in the
cytoplasm of the cells.
•
The set of chromosomes within a cell constitutes its genome, and within the genome are all the traits
for that particular organism.
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05/08/13
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Biology
HS/Science
Unit: 07 Lesson: 01
•
The traits specified for in a genome can be passed to offspring through asexual or sexual reproduction.
Information and graphics sources:
Griffiths A., Miller J., Suzuki D., et al. An Introduction to Genetic Analysis. 7th edition. New York: W. H. Freeman; 2000. Gene-protein relations. Available
from: http://www.ncbi.nlm.nih.gov/books/NBK21811/
Evers, C. (2013, May 5). The one gene/one enzyme hypothesis. Retrieved from
http://www.accessexcellence.org/RC/AB/BC/One_Gene_One_Enzyme.php
Unknown. (2013, April 22). The genetic code. Retrieved from http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/C/Codons.html
Unknown. (2013, May 5). Dna: The secret of life. Retrieved from http://topdocumentaryfilms.com/dna/
Unknown. (2013, April 23). What is dna?. Retrieved from http://ghr.nlm.nih.gov/handbook/basics/dna
Unknown. (2013, May 5). Dna is a structure that encodes biological information. Retrieved from http://www.nature.com/scitable/topicpage/dna-is-astructure-that-encodes-biological-6493050
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