DNA and RNA Structure and Function
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Questions and Answers

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.

RNA

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.

<p>guanine</p> Signup and view all the answers

The deoxyribose 5′ carbon may be bound to one, two, or three ______ groups.

<p>phosphate</p> Signup and view all the answers

RNA contains adenine, cytosine, and guanine but has ______ nucleotides in place of the thymines found in DNA.

<p>uracil</p> Signup and view all the answers

Nucleotide modifications can also result in nucleotides with new ______.

<p>properties</p> Signup and view all the answers

Gram-negative bacteria use modified nucleotides in a type of immune system, the ______ modification (rm) system.

<p>restriction</p> Signup and view all the answers

The bacterium adds ______ groups to its own DNA to distinguish it from that of invaders, such as bacterial viruses.

<p>methyl</p> Signup and view all the answers

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.

<p>phosphate</p> Signup and view all the answers

The length of a double-stranded DNA macromolecule is measured in ______.

<p>base pairs</p> Signup and view all the answers

DNA replication takes place during the ______ phase of the cell cycle.

<p>S</p> Signup and view all the answers

DNA synthesis cannot begin without a preexisting 3′ ______ group.

<p>hydroxyl</p> Signup and view all the answers

To begin synthesis in vivo, a ______ of RNA is synthesized by an RNA polymerase (primase) enzyme.

<p>primer</p> Signup and view all the answers

One strand, termed the ______ strand, is copied discontinuously toward the replication fork.

<p>lagging</p> Signup and view all the answers

RNA synthesis is catalyzed by ______ polymerase, which begins polymerization of RNA by binding to its recognition start site in DNA.

<p>RNA</p> Signup and view all the answers

RNA synthesis can start de novo without a ______.

<p>primer</p> Signup and view all the answers

The bulk of DNA synthesis takes place in the ______ phase of the cell cycle.

<p>S</p> Signup and view all the answers

A change in the nucleotide sequence in DNA is called a ______ or variant.

<p>mutation</p> Signup and view all the answers

The term ______ is recommended for nucleotide sequence changes that are inherited (germline).

<p>variant</p> Signup and view all the answers

Point mutations involve one or a few ______ pairs and are classified by their effect on the amino acid sequence.

<p>base</p> Signup and view all the answers

Conservative and silent mutations do not affect ______.

<p>phenotype</p> Signup and view all the answers

A mutation that replaces a guanidine with an adenosine nucleotide at position 2175 would be expressed as: ______G→A.

<p>2175</p> Signup and view all the answers

Alterations in DNA or protein sequences shared by at least 2% of a natural population are considered ______.

<p>polymorphisms</p> Signup and view all the answers

The different versions of the affected sequences are referred to as ______.

<p>alleles</p> Signup and view all the answers

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.

<p>beta-globin</p> Signup and view all the answers

The major histocompatibility (MHC) locus is located on chromosome ______.

<p>6</p> Signup and view all the answers

Each person will have a particular group of ______ alleles, which are inherited from his or her parents.

<p>HLA</p> Signup and view all the answers

HLA proteins coded for by these alleles play important roles in the ______ response

<p>immune</p> Signup and view all the answers

Polymorphisms are introduced in each cell through ______ genetic events

<p>cell-specific</p> Signup and view all the answers

These sequences differ from cell to cell, allowing for the generation of a large repertoire of ______ and antigen receptors

<p>antibodies</p> Signup and view all the answers

Polymorphisms that create, destroy, or otherwise affect sequences in DNA that are recognized by ______ enzymes are detected as RFLPs

<p>nuclease</p> Signup and view all the answers

STRs and VNTRs are head-to-tail repeats of a single base pair to more than ______ bp repeat units

<p>100</p> Signup and view all the answers

STR testing has replaced RFLP testing for human ______ in forensics

<p>identification</p> Signup and view all the answers

STRs and VNTRs are the markers commonly used to follow ______ of donor cells into recipient blood and bone marrow

<p>engraftment</p> Signup and view all the answers

STRs and VNTRs can be detected as RFLPs or by using ______ procedures

<p>amplification</p> Signup and view all the answers

Only about 2% of the RNA-coding regions are translated into ______.

<p>protein</p> Signup and view all the answers

Some genes code for ______ RNA and ribosomal RNA, which are required for translation of protein-coding messenger RNA into protein.

<p>transfer</p> Signup and view all the answers

Large portions of the genome are occupied by ______, DNA elements that can move from one location to another through an RNA intermediate.

<p>retrotransposons</p> Signup and view all the answers

Noncoding RNA, along with methylated nucleotides and modified ______ proteins associated with DNA, are considered epigenetic mechanisms.

<p>histone</p> Signup and view all the answers

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.

<p>mRNA</p> Signup and view all the answers

Each mRNA is marked by a guanidine nucleotide covalently attached to its 5′ end in an unusual 5′–5′ ______ (cap).

<p>bond</p> Signup and view all the answers

Ribosomes are organelles that are composed of ribosomal proteins and ribosomal ______.

<p>RNA</p> Signup and view all the answers

The codons are carried from the nucleus to the cytoplasm in mRNA to be translated into ______.

<p>protein</p> Signup and view all the answers

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.

<p>complementary</p> Signup and view all the answers

Newly synthesized proteins are directed through the ______ reticulum of the cell to their final destination.

<p>endoplasmic</p> Signup and view all the answers

What is the primary function of DNA within chromosomes found in each cell?

<p>To carry the primary genetic information</p> Signup and view all the answers

Which of the following is NOT a type of RNA?

<p>deoxyribonucleic acid RNA (drRNA)</p> Signup and view all the answers

What is attached to the 1′ carbon of the deoxyribose sugar in a nucleotide?

<p>A nitrogen base</p> Signup and view all the answers

What is the purpose of modified nucleotides in the restriction modification (rm) system of Gram-negative bacteria?

<p>To distinguish between self and non-self DNA</p> Signup and view all the answers

What is the result of nucleotide base modifications caused by environmental insults?

<p>Mutations</p> Signup and view all the answers

What is the difference between deoxyribonucleotides and ribonucleotides?

<p>Ribonucleotides have a hydroxyl group on the 2′ carbon, while deoxyribonucleotides do not</p> Signup and view all the answers

What is the result of the addition and removal of methyl groups (–CH3) to DNA?

<p>Gene silencing</p> Signup and view all the answers

What is the purpose of nucleotide modifications in the cell?

<p>To alter gene function</p> Signup and view all the answers

What percentage of RNA-coding regions are translated into protein?

<p>2%</p> Signup and view all the answers

What is the function of transfer RNA and ribosomal RNA?

<p>To translate mRNA into protein</p> Signup and view all the answers

What type of DNA elements can move from one location to another through an RNA intermediate?

<p>Retrotransposons</p> Signup and view all the answers

What is the term for chemical changes in histone proteins, modification of DNA, and noncoding RNA activities that influence gene expression?

<p>Epigenetics</p> Signup and view all the answers

What is the process called when genetic information flows from DNA to mRNA?

<p>Transcription</p> Signup and view all the answers

What is the structure attached to the 5′ end of mRNA?

<p>Cap</p> Signup and view all the answers

What is the function of ribosomes?

<p>To translate mRNA into protein</p> Signup and view all the answers

What carries the codons from the nucleus to the cytoplasm?

<p>mRNA</p> Signup and view all the answers

What is the term for a nucleotide sequence change that occurs spontaneously in DNA?

<p>Mutation</p> Signup and view all the answers

What is the function of the anti-codon on tRNA?

<p>To recognize the codon on mRNA</p> Signup and view all the answers

Where are newly synthesized proteins directed?

<p>Endoplasmic reticulum</p> Signup and view all the answers

Which type of mutation will likely affect protein structure or function?

<p>Nonconservative mutation</p> Signup and view all the answers

What is the notation for a mutation that replaces a guanidine with an adenosine nucleotide at position 2175?

<p>2175G→A</p> Signup and view all the answers

What is the frequency of occurrence for a nucleotide sequence change to be considered a polymorphism?

<p>At least 2% of a natural population</p> Signup and view all the answers

What is the term for the different versions of the affected sequences in a polymorphism?

<p>Alleles</p> Signup and view all the answers

Which gene on chromosome 11 is associated with sickle cell anemia?

<p>Beta-globin gene</p> Signup and view all the answers

Where is the major histocompatibility (MHC) locus located?

<p>Chromosome 6</p> Signup and view all the answers

What is the result of a mutation that replaces a glutamic acid with a valine at position 6 in the protein sequence?

<p>Abnormal red blood cells that do not circulate efficiently</p> Signup and view all the answers

What is the benefit of having a particular polymorphism that causes sickle cell anemia?

<p>Resistance to malaria</p> Signup and view all the answers

What is the role of HLA alleles in the human body?

<p>They play a role in the immune response</p> Signup and view all the answers

What is the purpose of adding methyl groups to the bacterium's own DNA?

<p>To distinguish its own DNA from that of viral invaders</p> Signup and view all the answers

What is the direction of DNA synthesis during replication?

<p>5′ to 3′</p> Signup and view all the answers

What is the role of RNA polymerase in RNA synthesis?

<p>To catalyze RNA synthesis</p> Signup and view all the answers

What is the term for the length of a single strand of RNA or DNA?

<p>Base</p> Signup and view all the answers

What is the phase of the cell cycle during which DNA replication takes place?

<p>S phase</p> Signup and view all the answers

What is the term for the process of DNA replication?

<p>Semi-conservative</p> Signup and view all the answers

What is the requirement for DNA synthesis to begin?

<p>A preexisting 3′ hydroxyl group</p> Signup and view all the answers

What is the term for the strand that is copied discontinuously towards the replication fork?

<p>Lagging strand</p> Signup and view all the answers

What is the direction in which the parental template strand is read during DNA replication?

<p>3′ to 5′</p> Signup and view all the answers

What is the term for the enzyme that catalyzes the formation of phosphodiester bonds during DNA replication?

<p>DNA polymerase</p> Signup and view all the answers

What is the primary function of HLA proteins in the immune response?

<p>To differentiate between self and non-self</p> Signup and view all the answers

What type of genetic events introduce polymorphisms in each cell?

<p>Cell-specific genetic events</p> Signup and view all the answers

What is the purpose of somatic hypermutation in the generation of antibodies and antigen receptors?

<p>To increase the diversity of antibodies and antigen receptors</p> Signup and view all the answers

What type of polymorphisms are detected as restriction fragment length variations or polymorphisms (RFLPs)?

<p>Polymorphisms that affect sequences recognized by nuclease enzymes</p> Signup and view all the answers

What is the range of repeat units in short tandem repeats (STRs) and variable-number tandem repeats (VNTRs)?

<p>1-100 bp</p> Signup and view all the answers

What is the application of STR testing in forensics?

<p>Human identification</p> Signup and view all the answers

What is the purpose of using STRs and VNTRs in allogeneic bone marrow transplantation?

<p>To follow engraftment of donor cells</p> Signup and view all the answers

What is the mechanism by which STRs and VNTRs can be detected?

<p>RFLPs or amplification procedures</p> Signup and view all the answers

What is the function of the hydroxyl group on the 3′ carbon of the deoxyribose sugar?

<p>To bind to the 5′ phosphate group of the adjacent nucleotide</p> Signup and view all the answers

What is the result of the addition of a methyl group to DNA?

<p>Inhibition of gene function</p> Signup and view all the answers

What is the significance of the 2′ and 3′ hydroxyl groups on the ribose sugar in RNA?

<p>They are characteristic of RNA but not DNA</p> Signup and view all the answers

What is the purpose of nucleotide modifications in the cell?

<p>To recognize and distinguish self from non-self</p> Signup and view all the answers

What is the difference between the nitrogen bases found in DNA and RNA?

<p>DNA has adenine, cytosine, guanine, and thymine, while RNA has adenine, cytosine, guanine, and uracil</p> Signup and view all the answers

What is the consequence of nucleotide modifications on gene function?

<p>It can either activate or inhibit gene function</p> Signup and view all the answers

What is the role of the phosphorylated ribose sugar in RNA?

<p>To carry a phosphate group</p> Signup and view all the answers

What is the significance of the nitrogen base ring positions being numbered ordinally?

<p>It allows for the determination of the nucleotide structure</p> Signup and view all the answers

What is the purpose of the methyl groups added to the bacterium's own DNA?

<p>To recognize and target the invader's DNA for degradation</p> Signup and view all the answers

Which of the following nucleotide bases is NOT complementary to adenine?

<p>Cytosine</p> Signup and view all the answers

What is the direction of DNA synthesis during replication?

<p>5′ to 3′</p> Signup and view all the answers

What is the role of the primer in DNA synthesis?

<p>To provide a preexisting 3′ hydroxyl group</p> Signup and view all the answers

What is the term for the process of synthesizing RNA without a primer?

<p>De novo synthesis</p> Signup and view all the answers

What is the term for the strand of DNA that is copied continuously in the direction of replication?

<p>Leading strand</p> Signup and view all the answers

What is the purpose of DNA polymerase during DNA replication?

<p>To catalyze the formation of phosphodiester bonds</p> Signup and view all the answers

What is the term for the length of a single strand of RNA or DNA?

<p>Base</p> Signup and view all the answers

What is the term for the process of copying both strands of DNA simultaneously in the same direction?

<p>Bidirectional synthesis</p> Signup and view all the answers

What is the term for the phase of the cell cycle where DNA synthesis takes place?

<p>S phase</p> Signup and view all the answers

What is the primary function of the 5′–5′ bond (cap) and polyadenylation at the 3′ end of mRNA?

<p>To maintain the stability of the mRNA and allow its recognition by the ribosomes</p> Signup and view all the answers

What is the role of epigenetic mechanisms in gene expression?

<p>To chemically modify histone proteins and DNA to influence gene expression</p> Signup and view all the answers

What is the function of tRNA in protein synthesis?

<p>To serve as adaptors between the nucleotide sequence in the RNA and the amino acid sequence in proteins</p> Signup and view all the answers

What is the significance of the codon sequence in mRNA?

<p>It influences the translation of mRNA into protein</p> Signup and view all the answers

What is the role of ribosomes in protein synthesis?

<p>To translate mRNA into protein</p> Signup and view all the answers

What is the function of the ribosomal RNA (rRNA) in ribosomes?

<p>To compose the ribosomes and facilitate protein synthesis</p> Signup and view all the answers

What is the result of the translation of mRNA into protein?

<p>A newly synthesized protein chain</p> Signup and view all the answers

What is the role of the anti-codon sequence in tRNA?

<p>To recognize the codon sequence in mRNA</p> Signup and view all the answers

What is the significance of the 3-base recognition sequence (codon) in mRNA?

<p>It influences the translation of mRNA into protein</p> Signup and view all the answers

What is the fate of newly synthesized proteins after translation?

<p>They are directed through the endoplasmic reticulum to their final destination</p> Signup and view all the answers

What is the primary function of HLA proteins in the immune response?

<p>To differentiate between 'self' and 'non-self' cells</p> Signup and view all the answers

What is the mechanism by which polymorphisms are introduced in each cell?

<p>Cell-specific genetic events followed by somatic mutation</p> Signup and view all the answers

What is the purpose of RFLPs in the detection of polymorphisms?

<p>To detect polymorphisms that affect sequences recognized by nuclease enzymes</p> Signup and view all the answers

What is the main difference between STRs and VNTRs?

<p>The number of repeat units</p> Signup and view all the answers

Why are STRs and VNTRs commonly used in forensic science?

<p>Because they are highly polymorphic and can be used for human identification</p> Signup and view all the answers

What is the advantage of using STRs over RFLPs in human identification?

<p>STRs are easier to analyze</p> Signup and view all the answers

What is the role of HLA alleles in parentage testing?

<p>To determine the genetic relationship between individuals</p> Signup and view all the answers

What is the significance of polymorphisms in the immune response?

<p>They generate a large repertoire of antibodies and antigen receptors</p> Signup and view all the answers

What is the primary effect of conservative mutations on the amino acid sequence?

<p>They do not affect the function of the protein</p> Signup and view all the answers

What is the term for nucleotide sequence changes that are shared by at least 2% of a natural population?

<p>Polymorphism</p> Signup and view all the answers

What is the purpose of the notation 'c.' in the expression 'c.G2175A'?

<p>To indicate that the mutation is in complementary DNA</p> Signup and view all the answers

What is the effect of a frameshift mutation on the protein sequence?

<p>It changes the reading frame of the protein sequence</p> Signup and view all the answers

What is the term for the different versions of a sequence that are affected by a polymorphism?

<p>Alleles</p> Signup and view all the answers

What is the benefit of the polymorphism that causes sickle cell anemia?

<p>It provides resistance to Plasmodium species</p> Signup and view all the answers

What is the location of the major histocompatibility (MHC) locus?

<p>Chromosome 6</p> Signup and view all the answers

What is the effect of a nonsense mutation on the protein sequence?

<p>It introduces a premature stop codon</p> Signup and view all the answers

What is the purpose of the notation 'p.' in the expression 'p.G339V'?

<p>To indicate the location of the mutation in the protein sequence</p> Signup and view all the answers

What is the term for the change in the nucleotide sequence in DNA?

<p>Mutation</p> Signup and view all the answers

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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Learn about the two main types of nucleic acids, DNA and RNA, their composition, and their roles in genetics. Understand the different types of RNA and their functions.

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