Podcast
Questions and Answers
The two main kinds of nucleic acids are ______ and RNA.
The two main kinds of nucleic acids are ______ and RNA.
DNA
There are different types of ______, including messenger RNA (mRNA), transfer RNA (tRNA), ribosomal RNA (rRNA), and noncoding RNA.
There are different types of ______, including messenger RNA (mRNA), transfer RNA (tRNA), ribosomal RNA (rRNA), and noncoding RNA.
RNA
A nucleotide is composed of a phosphorylated ______ sugar and a nitrogen base.
A nucleotide is composed of a phosphorylated ______ sugar and a nitrogen base.
deoxyribose or ribose
The nitrogen base of a nucleotide, either ______, adenine, cytosine, or thymine, is attached to the 1′ carbon of the deoxyribose sugar.
The nitrogen base of a nucleotide, either ______, adenine, cytosine, or thymine, is attached to the 1′ carbon of the deoxyribose sugar.
The deoxyribose 5′ carbon may be bound to one, two, or three ______ groups.
The deoxyribose 5′ carbon may be bound to one, two, or three ______ groups.
RNA contains adenine, cytosine, and guanine but has ______ nucleotides in place of the thymines found in DNA.
RNA contains adenine, cytosine, and guanine but has ______ nucleotides in place of the thymines found in DNA.
Nucleotide modifications can also result in nucleotides with new ______.
Nucleotide modifications can also result in nucleotides with new ______.
Gram-negative bacteria use modified nucleotides in a type of immune system, the ______ modification (rm) system.
Gram-negative bacteria use modified nucleotides in a type of immune system, the ______ modification (rm) system.
The bacterium adds ______ groups to its own DNA to distinguish it from that of invaders, such as bacterial viruses.
The bacterium adds ______ groups to its own DNA to distinguish it from that of invaders, such as bacterial viruses.
Nucleotides are polymerized into nucleic acids by attachment of the 3′ hydroxyl groups on the deoxyribose or ribose sugar to the 5′ ______ group of the adjacent nucleotide.
Nucleotides are polymerized into nucleic acids by attachment of the 3′ hydroxyl groups on the deoxyribose or ribose sugar to the 5′ ______ group of the adjacent nucleotide.
The length of a double-stranded DNA macromolecule is measured in ______.
The length of a double-stranded DNA macromolecule is measured in ______.
DNA replication takes place during the ______ phase of the cell cycle.
DNA replication takes place during the ______ phase of the cell cycle.
DNA synthesis cannot begin without a preexisting 3′ ______ group.
DNA synthesis cannot begin without a preexisting 3′ ______ group.
To begin synthesis in vivo, a ______ of RNA is synthesized by an RNA polymerase (primase) enzyme.
To begin synthesis in vivo, a ______ of RNA is synthesized by an RNA polymerase (primase) enzyme.
One strand, termed the ______ strand, is copied discontinuously toward the replication fork.
One strand, termed the ______ strand, is copied discontinuously toward the replication fork.
RNA synthesis is catalyzed by ______ polymerase, which begins polymerization of RNA by binding to its recognition start site in DNA.
RNA synthesis is catalyzed by ______ polymerase, which begins polymerization of RNA by binding to its recognition start site in DNA.
RNA synthesis can start de novo without a ______.
RNA synthesis can start de novo without a ______.
The bulk of DNA synthesis takes place in the ______ phase of the cell cycle.
The bulk of DNA synthesis takes place in the ______ phase of the cell cycle.
A change in the nucleotide sequence in DNA is called a ______ or variant.
A change in the nucleotide sequence in DNA is called a ______ or variant.
The term ______ is recommended for nucleotide sequence changes that are inherited (germline).
The term ______ is recommended for nucleotide sequence changes that are inherited (germline).
Point mutations involve one or a few ______ pairs and are classified by their effect on the amino acid sequence.
Point mutations involve one or a few ______ pairs and are classified by their effect on the amino acid sequence.
Conservative and silent mutations do not affect ______.
Conservative and silent mutations do not affect ______.
A mutation that replaces a guanidine with an adenosine nucleotide at position 2175 would be expressed as: ______G→A.
A mutation that replaces a guanidine with an adenosine nucleotide at position 2175 would be expressed as: ______G→A.
Alterations in DNA or protein sequences shared by at least 2% of a natural population are considered ______.
Alterations in DNA or protein sequences shared by at least 2% of a natural population are considered ______.
The different versions of the affected sequences are referred to as ______.
The different versions of the affected sequences are referred to as ______.
A well-known example of a polymorphism is the A to T base substitution in the ______ gene on chromosome 11 that causes sickle cell anemia.
A well-known example of a polymorphism is the A to T base substitution in the ______ gene on chromosome 11 that causes sickle cell anemia.
The major histocompatibility (MHC) locus is located on chromosome ______.
The major histocompatibility (MHC) locus is located on chromosome ______.
Each person will have a particular group of ______ alleles, which are inherited from his or her parents.
Each person will have a particular group of ______ alleles, which are inherited from his or her parents.
HLA proteins coded for by these alleles play important roles in the ______ response
HLA proteins coded for by these alleles play important roles in the ______ response
Polymorphisms are introduced in each cell through ______ genetic events
Polymorphisms are introduced in each cell through ______ genetic events
These sequences differ from cell to cell, allowing for the generation of a large repertoire of ______ and antigen receptors
These sequences differ from cell to cell, allowing for the generation of a large repertoire of ______ and antigen receptors
Polymorphisms that create, destroy, or otherwise affect sequences in DNA that are recognized by ______ enzymes are detected as RFLPs
Polymorphisms that create, destroy, or otherwise affect sequences in DNA that are recognized by ______ enzymes are detected as RFLPs
STRs and VNTRs are head-to-tail repeats of a single base pair to more than ______ bp repeat units
STRs and VNTRs are head-to-tail repeats of a single base pair to more than ______ bp repeat units
STR testing has replaced RFLP testing for human ______ in forensics
STR testing has replaced RFLP testing for human ______ in forensics
STRs and VNTRs are the markers commonly used to follow ______ of donor cells into recipient blood and bone marrow
STRs and VNTRs are the markers commonly used to follow ______ of donor cells into recipient blood and bone marrow
STRs and VNTRs can be detected as RFLPs or by using ______ procedures
STRs and VNTRs can be detected as RFLPs or by using ______ procedures
Only about 2% of the RNA-coding regions are translated into ______.
Only about 2% of the RNA-coding regions are translated into ______.
Some genes code for ______ RNA and ribosomal RNA, which are required for translation of protein-coding messenger RNA into protein.
Some genes code for ______ RNA and ribosomal RNA, which are required for translation of protein-coding messenger RNA into protein.
Large portions of the genome are occupied by ______, DNA elements that can move from one location to another through an RNA intermediate.
Large portions of the genome are occupied by ______, DNA elements that can move from one location to another through an RNA intermediate.
Noncoding RNA, along with methylated nucleotides and modified ______ proteins associated with DNA, are considered epigenetic mechanisms.
Noncoding RNA, along with methylated nucleotides and modified ______ proteins associated with DNA, are considered epigenetic mechanisms.
The central dogma of genetics states that genetic information flows from DNA to ______, the process of transcription, and from mRNA to protein, the process called translation.
The central dogma of genetics states that genetic information flows from DNA to ______, the process of transcription, and from mRNA to protein, the process called translation.
Each mRNA is marked by a guanidine nucleotide covalently attached to its 5′ end in an unusual 5′–5′ ______ (cap).
Each mRNA is marked by a guanidine nucleotide covalently attached to its 5′ end in an unusual 5′–5′ ______ (cap).
Ribosomes are organelles that are composed of ribosomal proteins and ribosomal ______.
Ribosomes are organelles that are composed of ribosomal proteins and ribosomal ______.
The codons are carried from the nucleus to the cytoplasm in mRNA to be translated into ______.
The codons are carried from the nucleus to the cytoplasm in mRNA to be translated into ______.
Each tRNA, folded into an inverted “L”-like structure, carries an amino acid at the 3′ end and a 3-base ______ sequence (anti-codon) to the codon of that amino acid.
Each tRNA, folded into an inverted “L”-like structure, carries an amino acid at the 3′ end and a 3-base ______ sequence (anti-codon) to the codon of that amino acid.
Newly synthesized proteins are directed through the ______ reticulum of the cell to their final destination.
Newly synthesized proteins are directed through the ______ reticulum of the cell to their final destination.
What is the primary function of DNA within chromosomes found in each cell?
What is the primary function of DNA within chromosomes found in each cell?
Which of the following is NOT a type of RNA?
Which of the following is NOT a type of RNA?
What is attached to the 1′ carbon of the deoxyribose sugar in a nucleotide?
What is attached to the 1′ carbon of the deoxyribose sugar in a nucleotide?
What is the purpose of modified nucleotides in the restriction modification (rm) system of Gram-negative bacteria?
What is the purpose of modified nucleotides in the restriction modification (rm) system of Gram-negative bacteria?
What is the result of nucleotide base modifications caused by environmental insults?
What is the result of nucleotide base modifications caused by environmental insults?
What is the difference between deoxyribonucleotides and ribonucleotides?
What is the difference between deoxyribonucleotides and ribonucleotides?
What is the result of the addition and removal of methyl groups (–CH3) to DNA?
What is the result of the addition and removal of methyl groups (–CH3) to DNA?
What is the purpose of nucleotide modifications in the cell?
What is the purpose of nucleotide modifications in the cell?
What percentage of RNA-coding regions are translated into protein?
What percentage of RNA-coding regions are translated into protein?
What is the function of transfer RNA and ribosomal RNA?
What is the function of transfer RNA and ribosomal RNA?
What type of DNA elements can move from one location to another through an RNA intermediate?
What type of DNA elements can move from one location to another through an RNA intermediate?
What is the term for chemical changes in histone proteins, modification of DNA, and noncoding RNA activities that influence gene expression?
What is the term for chemical changes in histone proteins, modification of DNA, and noncoding RNA activities that influence gene expression?
What is the process called when genetic information flows from DNA to mRNA?
What is the process called when genetic information flows from DNA to mRNA?
What is the structure attached to the 5′ end of mRNA?
What is the structure attached to the 5′ end of mRNA?
What is the function of ribosomes?
What is the function of ribosomes?
What carries the codons from the nucleus to the cytoplasm?
What carries the codons from the nucleus to the cytoplasm?
What is the term for a nucleotide sequence change that occurs spontaneously in DNA?
What is the term for a nucleotide sequence change that occurs spontaneously in DNA?
What is the function of the anti-codon on tRNA?
What is the function of the anti-codon on tRNA?
Where are newly synthesized proteins directed?
Where are newly synthesized proteins directed?
Which type of mutation will likely affect protein structure or function?
Which type of mutation will likely affect protein structure or function?
What is the notation for a mutation that replaces a guanidine with an adenosine nucleotide at position 2175?
What is the notation for a mutation that replaces a guanidine with an adenosine nucleotide at position 2175?
What is the frequency of occurrence for a nucleotide sequence change to be considered a polymorphism?
What is the frequency of occurrence for a nucleotide sequence change to be considered a polymorphism?
What is the term for the different versions of the affected sequences in a polymorphism?
What is the term for the different versions of the affected sequences in a polymorphism?
Which gene on chromosome 11 is associated with sickle cell anemia?
Which gene on chromosome 11 is associated with sickle cell anemia?
Where is the major histocompatibility (MHC) locus located?
Where is the major histocompatibility (MHC) locus located?
What is the result of a mutation that replaces a glutamic acid with a valine at position 6 in the protein sequence?
What is the result of a mutation that replaces a glutamic acid with a valine at position 6 in the protein sequence?
What is the benefit of having a particular polymorphism that causes sickle cell anemia?
What is the benefit of having a particular polymorphism that causes sickle cell anemia?
What is the role of HLA alleles in the human body?
What is the role of HLA alleles in the human body?
What is the purpose of adding methyl groups to the bacterium's own DNA?
What is the purpose of adding methyl groups to the bacterium's own DNA?
What is the direction of DNA synthesis during replication?
What is the direction of DNA synthesis during replication?
What is the role of RNA polymerase in RNA synthesis?
What is the role of RNA polymerase in RNA synthesis?
What is the term for the length of a single strand of RNA or DNA?
What is the term for the length of a single strand of RNA or DNA?
What is the phase of the cell cycle during which DNA replication takes place?
What is the phase of the cell cycle during which DNA replication takes place?
What is the term for the process of DNA replication?
What is the term for the process of DNA replication?
What is the requirement for DNA synthesis to begin?
What is the requirement for DNA synthesis to begin?
What is the term for the strand that is copied discontinuously towards the replication fork?
What is the term for the strand that is copied discontinuously towards the replication fork?
What is the direction in which the parental template strand is read during DNA replication?
What is the direction in which the parental template strand is read during DNA replication?
What is the term for the enzyme that catalyzes the formation of phosphodiester bonds during DNA replication?
What is the term for the enzyme that catalyzes the formation of phosphodiester bonds during DNA replication?
What is the primary function of HLA proteins in the immune response?
What is the primary function of HLA proteins in the immune response?
What type of genetic events introduce polymorphisms in each cell?
What type of genetic events introduce polymorphisms in each cell?
What is the purpose of somatic hypermutation in the generation of antibodies and antigen receptors?
What is the purpose of somatic hypermutation in the generation of antibodies and antigen receptors?
What type of polymorphisms are detected as restriction fragment length variations or polymorphisms (RFLPs)?
What type of polymorphisms are detected as restriction fragment length variations or polymorphisms (RFLPs)?
What is the range of repeat units in short tandem repeats (STRs) and variable-number tandem repeats (VNTRs)?
What is the range of repeat units in short tandem repeats (STRs) and variable-number tandem repeats (VNTRs)?
What is the application of STR testing in forensics?
What is the application of STR testing in forensics?
What is the purpose of using STRs and VNTRs in allogeneic bone marrow transplantation?
What is the purpose of using STRs and VNTRs in allogeneic bone marrow transplantation?
What is the mechanism by which STRs and VNTRs can be detected?
What is the mechanism by which STRs and VNTRs can be detected?
What is the function of the hydroxyl group on the 3′ carbon of the deoxyribose sugar?
What is the function of the hydroxyl group on the 3′ carbon of the deoxyribose sugar?
What is the result of the addition of a methyl group to DNA?
What is the result of the addition of a methyl group to DNA?
What is the significance of the 2′ and 3′ hydroxyl groups on the ribose sugar in RNA?
What is the significance of the 2′ and 3′ hydroxyl groups on the ribose sugar in RNA?
What is the purpose of nucleotide modifications in the cell?
What is the purpose of nucleotide modifications in the cell?
What is the difference between the nitrogen bases found in DNA and RNA?
What is the difference between the nitrogen bases found in DNA and RNA?
What is the consequence of nucleotide modifications on gene function?
What is the consequence of nucleotide modifications on gene function?
What is the role of the phosphorylated ribose sugar in RNA?
What is the role of the phosphorylated ribose sugar in RNA?
What is the significance of the nitrogen base ring positions being numbered ordinally?
What is the significance of the nitrogen base ring positions being numbered ordinally?
What is the purpose of the methyl groups added to the bacterium's own DNA?
What is the purpose of the methyl groups added to the bacterium's own DNA?
Which of the following nucleotide bases is NOT complementary to adenine?
Which of the following nucleotide bases is NOT complementary to adenine?
What is the direction of DNA synthesis during replication?
What is the direction of DNA synthesis during replication?
What is the role of the primer in DNA synthesis?
What is the role of the primer in DNA synthesis?
What is the term for the process of synthesizing RNA without a primer?
What is the term for the process of synthesizing RNA without a primer?
What is the term for the strand of DNA that is copied continuously in the direction of replication?
What is the term for the strand of DNA that is copied continuously in the direction of replication?
What is the purpose of DNA polymerase during DNA replication?
What is the purpose of DNA polymerase during DNA replication?
What is the term for the length of a single strand of RNA or DNA?
What is the term for the length of a single strand of RNA or DNA?
What is the term for the process of copying both strands of DNA simultaneously in the same direction?
What is the term for the process of copying both strands of DNA simultaneously in the same direction?
What is the term for the phase of the cell cycle where DNA synthesis takes place?
What is the term for the phase of the cell cycle where DNA synthesis takes place?
What is the primary function of the 5′–5′ bond (cap) and polyadenylation at the 3′ end of mRNA?
What is the primary function of the 5′–5′ bond (cap) and polyadenylation at the 3′ end of mRNA?
What is the role of epigenetic mechanisms in gene expression?
What is the role of epigenetic mechanisms in gene expression?
What is the function of tRNA in protein synthesis?
What is the function of tRNA in protein synthesis?
What is the significance of the codon sequence in mRNA?
What is the significance of the codon sequence in mRNA?
What is the role of ribosomes in protein synthesis?
What is the role of ribosomes in protein synthesis?
What is the function of the ribosomal RNA (rRNA) in ribosomes?
What is the function of the ribosomal RNA (rRNA) in ribosomes?
What is the result of the translation of mRNA into protein?
What is the result of the translation of mRNA into protein?
What is the role of the anti-codon sequence in tRNA?
What is the role of the anti-codon sequence in tRNA?
What is the significance of the 3-base recognition sequence (codon) in mRNA?
What is the significance of the 3-base recognition sequence (codon) in mRNA?
What is the fate of newly synthesized proteins after translation?
What is the fate of newly synthesized proteins after translation?
What is the primary function of HLA proteins in the immune response?
What is the primary function of HLA proteins in the immune response?
What is the mechanism by which polymorphisms are introduced in each cell?
What is the mechanism by which polymorphisms are introduced in each cell?
What is the purpose of RFLPs in the detection of polymorphisms?
What is the purpose of RFLPs in the detection of polymorphisms?
What is the main difference between STRs and VNTRs?
What is the main difference between STRs and VNTRs?
Why are STRs and VNTRs commonly used in forensic science?
Why are STRs and VNTRs commonly used in forensic science?
What is the advantage of using STRs over RFLPs in human identification?
What is the advantage of using STRs over RFLPs in human identification?
What is the role of HLA alleles in parentage testing?
What is the role of HLA alleles in parentage testing?
What is the significance of polymorphisms in the immune response?
What is the significance of polymorphisms in the immune response?
What is the primary effect of conservative mutations on the amino acid sequence?
What is the primary effect of conservative mutations on the amino acid sequence?
What is the term for nucleotide sequence changes that are shared by at least 2% of a natural population?
What is the term for nucleotide sequence changes that are shared by at least 2% of a natural population?
What is the purpose of the notation 'c.' in the expression 'c.G2175A'?
What is the purpose of the notation 'c.' in the expression 'c.G2175A'?
What is the effect of a frameshift mutation on the protein sequence?
What is the effect of a frameshift mutation on the protein sequence?
What is the term for the different versions of a sequence that are affected by a polymorphism?
What is the term for the different versions of a sequence that are affected by a polymorphism?
What is the benefit of the polymorphism that causes sickle cell anemia?
What is the benefit of the polymorphism that causes sickle cell anemia?
What is the location of the major histocompatibility (MHC) locus?
What is the location of the major histocompatibility (MHC) locus?
What is the effect of a nonsense mutation on the protein sequence?
What is the effect of a nonsense mutation on the protein sequence?
What is the purpose of the notation 'p.' in the expression 'p.G339V'?
What is the purpose of the notation 'p.' in the expression 'p.G339V'?
What is the term for the change in the nucleotide sequence in DNA?
What is the term for the change in the nucleotide sequence in DNA?
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Study Notes
Nucleic Acids
- DNA (Deoxyribonucleic acid) and RNA (Ribonucleic acid) are the two main types of nucleic acids
- DNA carries genetic information within chromosomes found in each cell
- RNA has different types: messenger RNA (mRNA), transfer RNA (tRNA), ribosomal RNA (rRNA), and noncoding RNA
Nucleotide Structure
- A nucleotide is composed of:
- Phosphorylated deoxyribose or ribose sugar
- Nitrogen base (adenine (A), cytosine (C), guanine (G), thymine (T), or uracil (U))
- Nitrogen base ring positions are numbered ordinally, and ribose ring positions are numbered with prime numbers
- RNA contains adenine, cytosine, and guanine, but has uracil nucleotides in place of thymine
Substituted Nucleotides
- Natural modifications of the nucleotide structure include:
- Methylation
- Deamination
- Additions
- Substitutions
- Other chemical modifications
- These modifications can:
- Affect gene function
- Result in nucleotides with new properties
Nucleic Acid Polymer
- Nucleotides are polymerized into nucleic acids by attachment of the 3' hydroxyl group to the 5' phosphate group of the adjacent nucleotide
- Phosphodiester bonds form between nucleotides, giving the DNA strands polarity (5' phosphate end and 3' hydroxyl end)
- Sequences are ordered in the 5' to 3' direction
DNA Replication
- DNA replication takes place during the S phase of the cell cycle
- The cell cycle consists of four stages: G1, S, G2, and M
- DNA replication is semiconservative, with each strand serving as a template for a newly synthesized complementary strand
- DNA polymerase catalyzes the reaction, and synthesis proceeds in the 5' to 3' direction
RNA Synthesis
- RNA synthesis is catalyzed by RNA polymerase
- RNA polymerase begins polymerization of RNA by binding to its recognition start site in DNA (promoter)
- RNA synthesis can start de novo without a primer
- RNA polymerase is a more error-prone, slower polymerase than DNA polymerase
Protein Synthesis
- The central dogma of genetics states that genetic information flows from DNA to mRNA to protein
- Proteins are directly responsible for an organism's phenotype
- mRNA transcripts of protein-coding genes are translated into protein
- Ribosomes assemble on the mRNA for protein synthesis
- tRNA molecules serve as adaptors between the nucleotide sequence in the RNA and the amino acid sequence in proteins
DNA Sequence Changes
- A change in the nucleotide sequence in DNA is called a mutation or variant
- Mutations can range in size from a single base pair to millions of base pairs
- Point mutations involve one or a few base pairs and are classified by their effect on the amino acid sequence
- Mutations can affect protein structure or function, depending on their location in the protein sequence
Polymorphisms
- Structurally, mutations, variants, and polymorphisms are the same thing—changes in the reference amino acid or nucleotide sequence
- Alterations in DNA or protein sequences shared by at least 2% of a natural population are considered polymorphisms
- Polymorphic changes may or may not have phenotypic effects
- Examples of polymorphisms include:
- Single-nucleotide polymorphisms (SNPs)
- Restriction fragment length polymorphisms (RFLPs)
- Short tandem repeats (STRs) and variable-number tandem repeats (VNTRs)
Nucleic Acids
- DNA (Deoxyribonucleic acid) and RNA (Ribonucleic acid) are the two main types of nucleic acids
- DNA carries genetic information within chromosomes found in each cell
- RNA has different types: messenger RNA (mRNA), transfer RNA (tRNA), ribosomal RNA (rRNA), and noncoding RNA
Nucleotide Structure
- A nucleotide is composed of:
- Phosphorylated deoxyribose or ribose sugar
- Nitrogen base (adenine (A), cytosine (C), guanine (G), thymine (T), or uracil (U))
- Nitrogen base ring positions are numbered ordinally, and ribose ring positions are numbered with prime numbers
- RNA contains adenine, cytosine, and guanine, but has uracil nucleotides in place of thymine
Substituted Nucleotides
- Natural modifications of the nucleotide structure include:
- Methylation
- Deamination
- Additions
- Substitutions
- Other chemical modifications
- These modifications can:
- Affect gene function
- Result in nucleotides with new properties
Nucleic Acid Polymer
- Nucleotides are polymerized into nucleic acids by attachment of the 3' hydroxyl group to the 5' phosphate group of the adjacent nucleotide
- Phosphodiester bonds form between nucleotides, giving the DNA strands polarity (5' phosphate end and 3' hydroxyl end)
- Sequences are ordered in the 5' to 3' direction
DNA Replication
- DNA replication takes place during the S phase of the cell cycle
- The cell cycle consists of four stages: G1, S, G2, and M
- DNA replication is semiconservative, with each strand serving as a template for a newly synthesized complementary strand
- DNA polymerase catalyzes the reaction, and synthesis proceeds in the 5' to 3' direction
RNA Synthesis
- RNA synthesis is catalyzed by RNA polymerase
- RNA polymerase begins polymerization of RNA by binding to its recognition start site in DNA (promoter)
- RNA synthesis can start de novo without a primer
- RNA polymerase is a more error-prone, slower polymerase than DNA polymerase
Protein Synthesis
- The central dogma of genetics states that genetic information flows from DNA to mRNA to protein
- Proteins are directly responsible for an organism's phenotype
- mRNA transcripts of protein-coding genes are translated into protein
- Ribosomes assemble on the mRNA for protein synthesis
- tRNA molecules serve as adaptors between the nucleotide sequence in the RNA and the amino acid sequence in proteins
DNA Sequence Changes
- A change in the nucleotide sequence in DNA is called a mutation or variant
- Mutations can range in size from a single base pair to millions of base pairs
- Point mutations involve one or a few base pairs and are classified by their effect on the amino acid sequence
- Mutations can affect protein structure or function, depending on their location in the protein sequence
Polymorphisms
- Structurally, mutations, variants, and polymorphisms are the same thing—changes in the reference amino acid or nucleotide sequence
- Alterations in DNA or protein sequences shared by at least 2% of a natural population are considered polymorphisms
- Polymorphic changes may or may not have phenotypic effects
- Examples of polymorphisms include:
- Single-nucleotide polymorphisms (SNPs)
- Restriction fragment length polymorphisms (RFLPs)
- Short tandem repeats (STRs) and variable-number tandem repeats (VNTRs)
Nucleic Acids
- DNA (Deoxyribonucleic acid) and RNA (Ribonucleic acid) are the two main types of nucleic acids
- DNA carries genetic information within chromosomes found in each cell
- RNA has different types: messenger RNA (mRNA), transfer RNA (tRNA), ribosomal RNA (rRNA), and noncoding RNA
Nucleotide Structure
- A nucleotide is composed of:
- Phosphorylated deoxyribose or ribose sugar
- Nitrogen base (adenine (A), cytosine (C), guanine (G), thymine (T), or uracil (U))
- Nitrogen base ring positions are numbered ordinally, and ribose ring positions are numbered with prime numbers
- RNA contains adenine, cytosine, and guanine, but has uracil nucleotides in place of thymine
Substituted Nucleotides
- Natural modifications of the nucleotide structure include:
- Methylation
- Deamination
- Additions
- Substitutions
- Other chemical modifications
- These modifications can:
- Affect gene function
- Result in nucleotides with new properties
Nucleic Acid Polymer
- Nucleotides are polymerized into nucleic acids by attachment of the 3' hydroxyl group to the 5' phosphate group of the adjacent nucleotide
- Phosphodiester bonds form between nucleotides, giving the DNA strands polarity (5' phosphate end and 3' hydroxyl end)
- Sequences are ordered in the 5' to 3' direction
DNA Replication
- DNA replication takes place during the S phase of the cell cycle
- The cell cycle consists of four stages: G1, S, G2, and M
- DNA replication is semiconservative, with each strand serving as a template for a newly synthesized complementary strand
- DNA polymerase catalyzes the reaction, and synthesis proceeds in the 5' to 3' direction
RNA Synthesis
- RNA synthesis is catalyzed by RNA polymerase
- RNA polymerase begins polymerization of RNA by binding to its recognition start site in DNA (promoter)
- RNA synthesis can start de novo without a primer
- RNA polymerase is a more error-prone, slower polymerase than DNA polymerase
Protein Synthesis
- The central dogma of genetics states that genetic information flows from DNA to mRNA to protein
- Proteins are directly responsible for an organism's phenotype
- mRNA transcripts of protein-coding genes are translated into protein
- Ribosomes assemble on the mRNA for protein synthesis
- tRNA molecules serve as adaptors between the nucleotide sequence in the RNA and the amino acid sequence in proteins
DNA Sequence Changes
- A change in the nucleotide sequence in DNA is called a mutation or variant
- Mutations can range in size from a single base pair to millions of base pairs
- Point mutations involve one or a few base pairs and are classified by their effect on the amino acid sequence
- Mutations can affect protein structure or function, depending on their location in the protein sequence
Polymorphisms
- Structurally, mutations, variants, and polymorphisms are the same thing—changes in the reference amino acid or nucleotide sequence
- Alterations in DNA or protein sequences shared by at least 2% of a natural population are considered polymorphisms
- Polymorphic changes may or may not have phenotypic effects
- Examples of polymorphisms include:
- Single-nucleotide polymorphisms (SNPs)
- Restriction fragment length polymorphisms (RFLPs)
- Short tandem repeats (STRs) and variable-number tandem repeats (VNTRs)
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