Download video slide

The Genetic Code
• The genetic code is the set of
rules relating nucleotide
sequence to amino acid
sequence.
• The genetic code is shared by
all organisms.
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
• DNA specifies the synthesis of proteins in two
stages:
– Transcription
– Translation
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
From Nucleotides to Amino Acids: An Overview
• Genetic information in DNA is transcribed into
RNA and then translated into polypeptides.
• What is the language of nucleic acids?
– In DNA, it is the linear sequence of nucleotide
bases.
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Transcription: From DNA to RNA
• In transcription,
– Genetic information is transferred from DNA to
mRNA.
– An mRNA molecule is transcribed from a DNA
template.
http://www.stolaf.edu/people/giannini/flash
animat/molgenetics/transcription.swf
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
• When DNA is
transcribed, the result is
an mRNA molecule.
• RNA is then translated
into a sequence of
amino acids in a
polypeptide.
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Figure 10.13a
Transcribe this DNA template into a strand of
RNA:
• TAC AAC TAT TTT CGC CCG CGG ATT
• AUG UUG AUA AAA GCG GGC GCC UAA
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Answers to study guide page 59
I. Review the structure of DNA
1. DNA is a polymer called a nucleic acid.
2. The repeating units of DNA are called nucleotides.
3. Each DNA nucleotide is made of a phosphate, a
deoxyribose, and a nitrogen base.
4.
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Answers to study guide page 45 (continued)
5. How many nitrogen bases are possible in DNA? 4
Name them. A, T, G, C
How do the bases pair? A-T, G-C
What kind of bonds hold the bases together?
Hydrogen
6. What is the shape of the molecule? Double
helix
7. Where in the cell would you find DNA?
nucleus
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Answers to study guide page 45 (continued)
II. Describe the structure of RNA
1. RNA is a polymer called a nucleic acid.
2. The repeating units of RNA are called nucleotides.
3. Each RNA nucleotide is made of a phosphate, a
ribose, and a nitrogen base.
4.
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Answers to study guide page 45 (continued)
5. How many nitrogen bases are possible in RNA? 4
Name them. A, U, G, C
How do the bases pair? A-U, G-C
What kind of bonds hold the bases together?
Hydrogen
6. What is the shape of the molecule? Single
stranded, can form a ribosome or transfer RNA
7. Where in the cell would you find DNA?
Nucleus and Cytoplasm
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
III. Compare and Contrast DNA & RNA
Nucleic
Acid
Type of
Sugar
Bases
Possible
Shape
Location in
Cell
DNA
deoxyribose
A, T, G, C
Double helix
nucleus
RNA
ribose
A, U, G, C
Single
stranded
Nucleus &
cytoplasm
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
IV. Three types of RNA
Type of RNA
Location in Cell
Function
Messenger RNA
Nucleus & Cytoplasm
Carry “message” from
DNA in the nucleus
Transfer RNA
Cytoplasm
Deliver amino acids to
the mRNA
Ribosomal RNA
Cytoplasm
(originally made in
nucleolus)
Site of translation
(pairs tRNA with
mRNA)
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Protein Synthesis
The two steps in protein synthesis are:
-transcription- RNA polymerase transcribes a
gene (section of DNA) into a single strand of
messenger RNA
- translation- messenger RNA codes for a
sequence of amino acids which make up a
protein
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Figure 10.10
Messenger RNA (mRNA)
• mRNA carries the code in triplets of bases
– Specify all the amino acids.
– Are called codons.
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Figure 10.11
Transfer RNA (tRNA)
• tRNA
– delivers amino acids.
– Matches amino acids with codons in mRNA using
anticodons.
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Figure 10.15
Ribosomes
• Ribosomes
– Are structures that actually make proteins.
– Contain ribosomal RNA (rRNA).
– May be free floating or attached to the
endoplasmic reticulum.
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Figure 10.16a
• A fully assembled ribosome holds tRNA and
mRNA for use in translation.
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Figure 10.16b
Translation: The Process
• Translation is divided into three phases:
– Initiation -first amino acid attaches at start codon
– Elongation- additional amino acids added
– Termination- ribosome reaches stop codon
– Chain of amino acids complete
http://www.stolaf.edu/people/giannini/flashanimat/
molgenetics/translation.swf
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Figure 10.20
Mutations
• A mutation
– Is any change in the nucleotide sequence of DNA.
– Point mutations- one nitrogen base is substituted
for another (also called a base substitution)
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Figure 10.21
Figure 10.22a
• Base deletions- a nucleotide is deleted (removed)
from the sequence
• Base insertions- a nucleotide is added to the
sequence
• Insertions and deletions
– Can have disastrous effects.
– Change the reading frame of the genetic message.
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Figure 10.22b
Mutagens
• Mutations may result from
– Errors in DNA replication.
– Physical or chemical agents called mutagens.
• Radiation
• High Temperatures
• A variety of chemicals
– These external agents that cause mutations are
called mutagens.
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
More Important Facts
Mutagens break the chemical bonds of DNA or
cause unusual bonds to form.
A mutated gene will copy itself. AND, if this
mistake is copied into a sex cell (gamete), then
the mistake will affect the next generation.
Mutated body cells CANNOT pass on mutations
to next generation.
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
• Although mutations are often harmful,
– They are the source of the rich diversity of genes
in the living world.
– They contribute to the process of evolution by
natural selection.
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings