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2–3 Carbon Compounds
Nucleic Acids
Nucleic Acids
Nucleic acids are polymers assembled from
individual monomers known as nucleotides.
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Nucleic Acids
Nucleic acids store and transmit hereditary, or
genetic, information.
ribonucleic acid (RNA)
deoxyribonucleic acid (DNA)
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Structure of DNA
Deoxyribonucleic acid
* Sugar & phosphate
alternate to make up
the sides of the strand
**Found only in nucleus
Polymer of the monomer – Nucleotides
P
S N-base
Nucleotide
Single
nucleotide
5 carbon sugar –
deoxyribose
A phosphate
group
A nitrogen base
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Nucleic Acids
Nucleotides consist of three parts:
• a 5-carbon sugar
• a phosphate group
• a nitrogenous base
• Five types of bases:
Adenine (A) with T
Thymine (T) with A
Cytosine (C) with G
Guanine (G) with C
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RNA
Ribonucleic acid
The other Nucleic Acid
• Acts as a messenger between DNA and
the ribosomes and carries out protein
synthesis
• DNA is too large to get out of the nucleus;
it is also protected in the nucleus from
DNases. The cell uses RNA to bring its
message to the rest of the cell for protein
synthesis
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How DNA & RNA Differ:
* RNA is a single stranded
molecule
*RNA has ribose sugar instead of
deoxyribose
*RNA contains Uracil
in place of Thymine so
Adenine bonds with
Uracil
*RNA can be found in the nucleus,
cytoplasm
or at the ribosomes
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Let’s Review!!!
• Ribosomes are small organelles that are involved with
making proteins
• They are made up of proteins and rRNA
• They consist of two subunits – large and small
• Ribosomes are found both in the cytoplasm and on the
endoplasmic reticulum
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There are three different kinds of
RNA
• Messenger RNA (mRNA)
Formed in the nucleus and goes to the ribosomes; carries genetic
code from DNA through the cytoplasm to the ribosomes
• Transfer RNA (tRNA)
Shaped like T; carries amino acids to the mRNA on the ribosomes
• Ribosomal RNA (rRNA)
Most abundant; found in globular form (like a big glob) and makes
up the ribosomes
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The Process of
Protein Synthesis
* Process by which DNA codes for the production of
proteins (polypeptide chains) and protein assembly
- Polypeptide chains are polymers of the 20
different amino acids.
- Uses a genetic code – chemical letters in RNA that
make up words which code for particular amino
acids
- Check your understanding: what happens if the
letters change?
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Part I. Transcription of DNA into mRNA (the message)
•
FYI – any of the three types of RNA are made this way
DNA flattens and is unzipped exposing its bases (template) – sound familiar?
–
RNA polymerase binds free RNA nucleotides to exposed DNA bases
starting at a promoter – a specific DNA nucleotide pattern
–
Complementary base pairing occurs, EXCEPT THERE IS NO THYMINE IN
RNA. Instead, Adenine bonds with Uracil just as Thymine from DNA
would bond with Adenine.
–
Transcription continues until a termination signal is given (punctuation)
to stop the transcription process
–
If DNA reads: ATC GTC GAT TGG C AA
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The Genetic Code:
•
Where a group of 3 nucleotide bases translates into a particular amino
acid
•
This 3 “letter word” is called a codon
•
Codons are groups of 3 adjacent bases on mRNA (AAA, CCC GGG)
•
Each codon will specify a specific amino acid.
•
When the codon is recognized by the anticodon, this is called Translation
•
There are 64 different codons with punctuation as well for start and stop
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Stop Codons
Start codon
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…
About the genetic code
• Codons are code words found in mRNA
• Codons code for particular amino acids
• Three of the 64 codons are stop, one is
start – AUG = methionine
• The code is degenerate – more than one
codon can code for an amino acid – why is
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What is an
anticodon and
how does the
amino acid get
selected?
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Part II. Translation of mRNA into protein
* At the ribosome, the process of translation
occurs. Several ribosomes may undergo this
process at one time
• mRNA will temporarily bind with the two
ribosomal subunits
• tRNA is waiting in the cytoplasm with its
corresponding amino acid
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Polypeptide forming
Transcription
Translation
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• Once tRNA brings the correct amino acid to mRNA
at the ribosome, it releases and goes back to the
cytoplasm to pick up it corresponding amino acid
• Adjacent amino acids bond together, making a
peptide bond to form a polypeptide.
• Chain could be up to 10,000 amino acids long
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When things go wrong:
• Does this process ever make a mistake?
• Have you ever had to copy a large amount of
information?
• What is the likelihood of you making a mistake Slide
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or more?
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Changes in genetic materialGene Mutations:
alters one or more genes
Chromosomal Mutations:
alter the entire chromosome or a
portion of it.
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Gene
Mutations
Point Mutations – affect only one amino acid
Frameshift mutations – May affect an
entire amino acid sequence.
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•
Point
mutation
involves a change in one or a few nucleotides.
• Influences a single amino acid in the polypeptide change;
caused by a substitution of a nitrogen base.
• Sickle cell anemia is an example of this –
GUG instead of GAG
Valine instead of glutamic acid
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• THE FAT CAT ATE THE RAT
• Take out “C” in Cat & substitute a “B”
• THE FAT BAT ATE THE RAT
• In this case, it does not really change the
meaning to the sentence or the protein
formed
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• If DNA reads: A T G G T C
G A T T G G CAA
• mRNA:
C U A AC C GUU
UAC CAG
• Amino Acid:
Tyrosine - Glutamine – Leucine -Threonine – Valine
• But if mRNA: U A C C A G C A A AC C GUU
• The AA:
Tyrosine – Glutamine – Glutamine – Threonine – Valine
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•
Frameshift
mutation
involves a change in the entire protein
formed or a large portion of it.
• Caused by insertions (additions) or
deletions of nitrogen bases.
• Tay-Sachs is a disease caused by a
frameshift mutation
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• THE FAT CAT ATE THE RAT
• Take out “E” in THE & group into
3’s
• THF ATC ATA TET HER AT_
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• If DNA reads: A T G G T C
G A T T G G CAA
• mRNA:
C U A AC C GUU
• AA:
UAC CAG
Tyrosine - Glutamine – Leucine -Threonine – Valine
• BUT if mRNA:
UAC CAG UAA CCG
UU _
• THEN Amino Acid: Tyrosine - Glutamine – STOP!!!!
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• The entire sentence makes no sense. The protein formed would be
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totally different
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So which form
of a mutation
would be more
severe?
• Frameshift mutation …
since an entirely new protein
would be formed
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CHROMOSOMAL MUTATIONS
• involve changes in number and
structure of the chromosomes.
• Could change location of genes on
the chromosomes or the number of
copies of some of the genes.
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• Deletions – part of a chromosome is missing
Duplications – Extra copies of genes are
inserted
Chromosomal Mutations
animation
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Translocations
Parts of one non-homologous chromosome breaks
off and attached onto another non-homologous
chromosome
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