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2–3 Carbon Compounds
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Copyright Pearson Prentice Hall
Nucleic Acids
Nucleic Acids
Nucleic acids are polymers assembled from individual monomers known as nucleotides.
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Copyright Pearson Prentice Hall
Nucleic Acids
Nucleic acids store and transmit hereditary, or genetic, information.
ribonucleic acid (RNA)
deoxyribonucleic acid (DNA)
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Structure of DNAStructure of DNADeoxyribonucleic acid
Polymer of the monomer – Nucleotides
Single nucleotide
5 carbon sugar –deoxyribose
A phosphate group
A nitrogen base
S
PN-base
Nucleotide
* Sugar & phosphate alternate to make up the sides of the strand
**Found only in nucleus
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Copyright Pearson Prentice Hall
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 acidRibonucleic 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 The Process of Protein SynthesisProtein 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
– mRNA leaves the nucleus through a pore to go out into the cytosol to locate a ribosome
• mRNA: UAG CAG CUA ACC GUU
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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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Slide 12 of 37Start codon
Stop Codons
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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 this important?
• The code is UNIVERSAL!!!
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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
• Starting with the start codon (AUG), in groups of 3, mRNA will determine which amino acid tRNA must bring to the ribosome.
• Animation – Virtual Cell
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Transcription
Translation
Polypeptide forming
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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
• This continues until the entire message is translated.
• The chain of amino acids is formed called a polypeptide (protein). The translation ends when a STOP codon is reached (UAA, UAG, UGA).
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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 or more?
• What could cause these changes?
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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 MutationsPoint Mutations – affect only one amino acid
Frameshift mutationsFrameshift 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: U A C C A G C U A AC C GUU
• 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_
This makes no sense at all!!
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• If DNA reads: A T G G T C G A T T G G CAA
• mRNA: U A C C A G C U A AC C GUU
• AA: Tyrosine - Glutamine – Leucine -Threonine – Valine
• BUT if mRNA: U A C C A G U A A C C G U U _
• THEN Amino Acid: Tyrosine - Glutamine – STOP!!!!
• The entire sentence makes no sense. The protein formed would be totally different
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So which form of a mutation would be more severe?
• Frameshift mutation …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
• Inversions – Reverse direction of parts of the chromosome
Chromosomal Mutations animation
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Parts of one non-homologous chromosome breaks off and attached onto another non-homologous chromosome
Translocations
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