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Nucleic Acids
- - Molecules that store information for cellular growth and reproduction-DNA & RNA-Large molecules consisting of long chains of monomers called nucleotides found in the cell nucleus
- - Polymers of nucleotides or polynucleotides
- (nucleosides with a phosphate group bonded to -OH on C5')
- - Have a unique sequence of bases in RNA, which is called its primary structure
- - Carry information from one cell to the next
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DNA & RNA consist of:
- Monomers called nucleotides that consist of:
- -pentose sugar
- -base
- -phosphate
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Purines:
- - Adenine (A) *DNA & RNA
- - Guanine (G) *DNA & RNA
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Pyrimidines:
- - Cytosine (C) *DNA & RNA
- - Thymine (T) *DNA ONLY
- - Uracil (U) *RNA ONLY
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The bases in DNA & RNA are:
- - Pyrimidines C, T, and U
- - Purines A and G
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DNA contains the bases:
- - Cytosine (C)
- - Guanine (G)
- - Adenine (A)
- - Thymine (T) * different in DNA than in RNA
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RNA contains the bases:
- - Cytosine (C)
- - Guanine (G)
- - Adenine (A)
- - Uracil (U) * different in RNA than in DNA
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The pentose (5 carbon) sugar in RNA is:
- Ribose
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The pentose (5 carbon) sugar in DNA is:
- Deoxyribose with no O atom on carbon 2'
- - ' means prime
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A nucleoside is:
- - A combination of a sugar and a base
- - Has a base linked by a glycosidic bond to C1' of a sugar (ribose or deoxyribose)
- - Is named by changing the base ending to
- -osine for purines and -idine for pyrimidines
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A nucleotide is:
- - Formed when the phosphate group on C5' in the nucleoside group bonds to -OH on C5' of a ribose or deoxyribose sugar
- - Named using the name of the nucleoside, followed by 5'-monophosphate
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The nucleotides of RNA are identical to those of DNA except for:
In DNA the sugar is deoxyribose and deoxythymidine which replaces uridine.
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Components of DNA:
- - Bases: A,G,C and T
- - Sugar: Deoxyribose
- - Nucleoside: Base + deoxyribose sugar
- - Nucleotide: Base + deoxyribose sugar + phosphate
- - Nucleic Acid: Polymer of deoxyribose nucleotides
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Components of RNA:
- - Bases: A,G,C and U
- - Sugar: Ribose
- - Nucleoside: Base + ribose sugar
- - Nucleotide: Base + ribose sugar + phosphate
- - Nucleic Acid: Polymer of ribose nucleotides
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Nucleosides that contain a purine end with:
Nucleosides that contain a pyrimidine end with:
Nucleosides of DNA add:
- 1. -osine (Ex: adenosine/guanosine)
- 2. -idine (Ex: cytidine/thymidine)
- 3. deoxy to the beginning of their name
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Nucleic Acid Primary Structure:
- - Nucleotides are joined by a 3'-5' phosphodiester bond
- - The 3'-OH group of the sugar in one nucleotide forms an ester bond to the phosphate group on the 5'-carbon of the sugar of the next nucleotide
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Primary Structure of Nucleic Acids in DNA and RNA chains:
- - Each sugar in a sugar-phosphate backbone is attached to a base
- - The bases extend out from the nucleic acid backbone
- - Are labeled starting with the free 5' end to the 3' end
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DNA contains complementary base pairs, equal amounts of A and T and equal amounts of G and C bases in which:
- - Adenine is always linked by two hydrogen bonds with thymine (A-T)
- - Guanine is always linked by three hydrogen bonds with cytosine (G-C)
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Double Helix:
- - has two strands of nucleotides that wind together
- - is held in place by two hydrogen bonds that form between the base pairs A-T
- - is held in place by three hydrogen bonds that form between the base pairs G-C
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In the double helix of DNA:
- - the two chains are held together by hydrogen bonds that link bases A-T and G-C
- - the bases along one strand complement the bases along the other
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Write the complementary base sequence for the matching strand in the following DNA section:
-A-G-T-C-C-A-A-T-C-
-T-C-A-G-G-T-T-A-G-
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In DNA replication:
- - genetic information is maintained each time a cell divides
- - the DNA strands unwind
- - each parent strand bonds with new complementary bases
- - two new DNA strands form that are EXACT copies of the parent DNA
- - the separate strands of the parent DNA are the templates for the synthesis of complementary strands, which produces two exact copies (daughter DNAs)
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How many hydrogen bonds link each of the following base pairs?
1. A-T
2. G-C
- 1. Bases are linked by two hydrogen bonds
- 2. Bases are linked by three hydrogen bonds
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In DNA fingerprinting:
- - enzymes are used to cut DNA chains into smaller sections
- - the resulting fragments are separated by size and treated with a radioactive isotope that adheres to specific base sequences
- - the resulting pattern of bands are known as a DNA fingerprint
*One application of DNA fingerprinting is in forensic science, where DNA from samples such as blood, hair, or semen is used to connect a suspect with a crime
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RNA:
- - makes up most of the nucleic acid found in the cell
- - transmits the genetic information needed for cell operation
- - transmits information from DNA to make proteins
- - molecules are polymers of nucleotides and differ from DNA in four ways
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4 ways RNA differs from DNA:
- 1. The sugar in RNA is ribose rather than deoxyribose found in DNA
- 2. The base uracil replaces thymine
- 3. RNA molecules are single stranded; DNA is double stranded
- 4. RNA molecules are much smaller than DNA molecules
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Types of RNA:
- - Messenger RNA (mRNA)
- - Transfer RNA (tRNA)
- - Ribosomal RNA (rRNA)
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Messenger RNA:
- - rRNA
- - 5% of total RNA
- - Carries information for protein synthesis from the DNA in the nucleus to the ribosomes
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Transfer RNA:
- - tRNA
- - 15% of total RNA
- - Brings amino acids to the ribosomes for protein synthesis
- - smallest RNA, only type that can translate genetic information into amino acids for proteins
- - cloverleaf shape when hydrogen bonds form between its complementary bases
- - the acceptor stem attaches to an amino acid and its anticodon bonds with a condon on mRNA
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Ribosomal RNA:
- - rRNA
- - 80% of total RNA
- - Major component of the ribosomes; protein synthesis
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Protein Synthesis involves:
- - Transcription
- - Translation
*The genetic information in DNA is replicated in cell division and used to produce mRNAs that code for the amino acids needed for protein synthesis
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Transcription:
- - mRNA is formed from a gene on a DNA strand
- - begins when a section of DNA containing the gene unwinds
- - within the unwound DNA, RNA polymerase enzymes uses one of the strands as a template to synthesize mRNA
- - the mRNA is released at the termination point
- -mRNA is synthesized using complementary base pairing, with uracil (U) and thymine (T)
- - the newly formed mRNA moves out of the nucleus to ribosomes in the cytoplasm
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Translation:
tRNA molecules bring amino acids to mRNA to build a protein
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What is the sequence of bases in mRNA produced from a section of the template strand of DNA that has the sequence of bases:
-C-T-A-A-G-G-
-G-A-U-U-C-C-
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Genetic Code:
- - a series of three nucleotides in mRNA called codons that determine the amino acid order for the protein
- - has different codon for all 20 amino acids needed to build a protein
- - contains certain codons that signal the "start" and "end" of a polypeptide chain
*Ex: -UUU-UUU-UUU- codes for three phenylalanine amino acids:
- Codons in mRNA -UUU-UUU-UUU-
- Translation ↓ ↓ ↓
- Amino acid sequence -Phe-Phe-Phe-
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From Table 17.4, write the order of amino acids coded for by a section of mRNA with the base sequence:
-GCC-GUA-GAC-
- GCC = alanine
- GUA = valine
- GAC = aspartic acid
- -GCC-GUA-GAC-
- ↓ ↓ ↓
- Ala-Val-Asp
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Initiation of Protein Synthesis:
- - an mRNA attaches to a ribosome
- - the start codon (AUG) in mRNA forms hydrogen bonds to methionine on tRNA
- - the second codon attaches to a tRNA with the next amino acid
- - a peptide bond forms between the adjacent amino acids at the first and second codons
- - once the peptide bond is formed, the initial tRNA detaches from the ribosome, which shifts to the next available codon; this process is called translocation
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Chain Elongation:
- the ribosome moves along the mRNA from codon to codon, attaching new amino acids to the growing polypeptide chain
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Translocation:
- - the first tRNA detaches from the ribosome
- - the ribosome shifts to the adjacent codon on the mRNA
- - a new tRNA/amino acid attaches to the open binding site
- - a peptide bond forms and that tRNA detaches
- - the ribosome shifts down the mRNA to read the next codon
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Termination Step:
- - all amino acids are linked
- - the ribosome reaches a "stop" codon: UGA, UAA, or UAG
- - there is no tRNA with an anticodon for the "stop" codons
- - the polypeptide detaches from the ribosome
- - once the polypeptide is released, the R groups of the amino acids in the new polypeptide can form hydrogen bonds to give the secondary structures of alpha helices, beta pleated sheets, or triple helices
- - chains form cross-links such as salt bridges and disulfide bonds to produce tertiary and quaternary structures, which makes it a biologically active protein
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Which codons in mRNA act as stop signals rather than amino acids and code for the termination of protein synthesis?
UGA, UAA, and UAG
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When does this happen:
Ribosomes move along mRNA, adding amino acids to a growing peptide chain.
Translocation
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When does this happen:
A completed peptide chain is released.
Termination
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When does this happen:
A tRNA attaches to its specific amino acid.
Activation
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When does this happen:
A tRNA binds to the AUG codon of the mRNA on the ribosome.
Initiation
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Steps in Protein Synthesis:
1. DNA Transcription
- Site: Nucleus, nucleotides, RNA polymerase
- Process: A DNA template is used to produce mRNA
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Steps in Protein Synthesis:
2. Activation of tRNA
- Site: Cytoplasm, amino acids, tRNAs, aminoacyl tRNA sythetase
- Process: Molecules of tRNA pick up specific amino acids according to their anticodons
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Steps in Protein Synthesis:
3. Initiation and Chain Elongation
- Site: Ribosome, Met-tRNA, mRNA, amino acyl tRNAs
- Process: A start codon binds the first tRNA carrying amino acid methionine to the mRNA. Successive tRNAs bind to and detach from the ribosome as each amino acid adds to the polypeptide
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Steps in Protein Synthesis:
4. Chain Termination
- Site: Ribosome, stop codon on mRNA
- Process: A polypeptide is released from ribosome
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Complementary Sequences in DNA, mRNA, tRNA, and Peptides
- Nucleus:
- DNA coding strand: -GCG-AGT-GGA-TAC-
- DNA template strand: -CGC-TCA-CCT-ATG-
- Ribosome (cytoplasm):
- mRNA: -GCG-AGU-GGA-UAC-
- tRNA anticodons: -CGC-UCA-CCU-AUG-
- Polypeptide amino acids: -Ala-Ser-Gly-Tyr-
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The following section of DNA is used to build mRNA for a protein:
-GAA-CCC-TTT-
1. What is the corresponding mRNA sequence?
2. What are the anticodons on the tRNAs?
3. What is the amino acid order in the peptide?
1. -CUU-GGG-AAA-
2. GAA for CUU; CCC for GGG; UUU for AAA
3. Leu-Gly-Lys
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Place the following statements in order of their occurrence in protein synthesis:
A. mRNA attaches to a ribosome.
B. The ribosome moves along mRNA to add amino acids to the growing peptide chain.
C. A completed polypeptide is released.
D. A tRNA brings an amino acid to its codon on mRNA.
E. DNA produces mRNA.
- 1) E. DNA produces mRNA.
- 2) A. mRNA attaches to a ribosome.
- 3) D. A tRNA brings an amino acid to its codon on mRNA.
- 4) B. The ribosome moves along mRNA to add amino acids to the growing peptide chain.
- 5) C. A completed polypeptide is released.
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Mutation:
- - change in the nucleotide sequence of DNA;
- - result from mutagens such as radiation and chemicals
- - produce one or more incorrect codons in mRNA
- - produce a protein containing one or more incorrect amino acids
- - produce defective proteins and enzymes
- - cause genetic diseases
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Substitution or Point Mutation
- - replacement of one base in the template strand of DNA with another
- - If this changes the nucleotide, a different amino acid may be inserted into the polypeptide
- - if a base in DNA changes a codon in the mRNA
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Silent Mutation
- if a substitution or point mutation produces no change in the amino acid sequence
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Frameshift Mutation
- - insertion of a single nucleotide into the sequence resulting in a change to all subsequent codons, leading to a new amino acid sequence
- - an extra base adds to or is deleted from the normal DNA sequence
- - all the codons in mRNA and amino acids are incorrect from the base change
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Genetic Disease
- - Hereditary mutation causes a change in the amino acid sequence the structure of the resulting protein may be severely altered, causing loss of its biological activity.
- - altered enzymes cannot catalyze reactions, and possible toxins may accumulate in the body and may be lethal
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Examples of Genetic Diseases
- - Galactosemia
- - Cystic fibrosis
- - Down syndrome
- - Muscular dystrophy
- - Huntington's disease
- - Sickle cell anemia
- - Hemophilia
- - Tay Sachs disease
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Identify each type of mutation as a substitution or frameshift:
A. Cytosine (C) enters the DNA sequence.
B. One adenosine is removed from the DNA sequence.
C. A base sequence of TGA in DNA changes to TAA.
- A. Frameshift
- B. Frameshift
- C. Substitution
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Viruses
- - small particles of DNA or RNA that require a host cell to replicate
- - cause a viral infection when the DNA or RNA enters a host cell
- - are synthesized in the host cell from the viral RNA produced by viral DNA
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Stages of a Virus
- - after a virus attaches to the host cell, it injects its viral DNA and uses the host cell's amino acids to synthesize viral protein.
- - it uses the host cell's nucleic acids, enzymes, and ribosomes to make viral RNA.
- - when the cell bursts, the new viruses are released to infect other cells.
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Reverse Transcription
- - a retrovirus, which contains viral RNA but no viral DNA, enters a cell
- - the viral RNA uses reverse transcriptase to produce a viral DNA strand
- - the viral DNA strand forms a complementary DNA strand
- - the new DNA uses the nucleotides and enzymes in the host cell to synthesize new virus particles
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HIV-1 Virus
- - a retrovirus that infects T4 lymphocyte cells
- - decreases the T4 level and the immune system fails to destroy harmful organisms
- - causes pneumonia and skin cancer associated with AIDS
- - treatment for AIDS is based on attacking HIV-1 at different points in its life cycle, such as prevention of reverse transcription of the viral DNA and protein synthesis
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AZT
- similar to thymidine, mimics the structure of the nucleosides used for DNA synthesis, which inhibit the reverse transcriptase enzyme
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Lexiva
- protease inhibitor that prevents protein synthesis used by viruses to make more copies
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Match the following terms with the descriptions below:
virus, retrovirus, protease inhibitor, reverse transcription
A. A virus containing RNA
B. Small particles requiring host cells to replicate
C. A substance that prevents the synthesis of viral proteins
D. Using viral RNA to synthesize viral DNA
- A. retrovirus
- B. virus
- C. protease inhibitor
- D. reverse transcription
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Nucleic Acids are ? and ?
DNA and RNA
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DNA contains ? arranged as a ? with ? with an order called?
Deoxynucleotides A,T,G,C arranged as a double helix with complementary base pairs A-T, G-C with an order called Genetic Code.
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RNA contains ? with three types ? and ? and ?
Nucleotides A,U,G,C with three types mRNA and tRNA and rRNA.
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Protein Synthesis uses ? specific for ? produce a ?
Codons specific for Amino Acids produce a Protein.
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