Nucleic Acids and Their Components Quiz

Introduction

• Each cell in the human body contains many different proteins.
• Cells must choose which proteins to create from a large number of possible amino acids.
• Hereditary information is transmitted in the nucleus, specifically chromosomes.
• Chromosomes are largely made up of histones and nucleic acids.

Nucleic Acids

• Nucleic acids are the backbones of chromosomes
• They include Ribonucleic acid (RNA) and Deoxyribonucleic acid (DNA).

Nucleic Acids Details

• DNA stores an organism's genetic information and transmits it across generations.
• RNA translates DNA's genetic information into proteins needed for cellular functions.
• Both RNA and DNA are unbranched polymers consisting of nucleotides.

Nucleotide Structure

• A nucleotide is composed of:
  • Nitrogen-containing bases (amines)
  • Sugars (monosaccharides)
  • Phosphate

Bases

• DNA and RNA contain four bases:
  • Adenine (A)
  • Guanine (G)
  • Cytosine (C)
  • Thymine (T) (in DNA only)
  • Uracil (U) (in RNA only)

Sugars

• RNA contains D-ribose sugar
• DNA contains 2-deoxy-D-ribose sugar (lacks an oxygen on carbon 2)

Nucleoside

• Formed when a nitrogen atom of the base forms a glycosidic bond to a sugar's anomeric carbon.
• Nucleoside = Base + Sugar
• Named using suffixes (-idine for pyrimidines, -osine for purines, and prefix deoxy- for deoxyribonucleosides).

Nucleotide (continued)

• Nucleotides form when a sugar's 5' hydroxyl group bonds to a phosphate.
• Example: Cytidine 5'-monophosphate (abbreviated as CMP)
• Another example: Deoxyadenosine 5'-monophosphate (abbreviated as dAMP)

Primary Structure of DNA and RNA

• DNA/RNA are chains of nucleotides.
• The nucleotide sequence/order dictates the order of amino acids in the protein.
• Nucleotides are arranged from the 5' end (free phosphate) to the 3' end (free hydroxyl).
• The sequence is read from 5' end to 3' end.
• Examples: ACGU

Secondary Structure of DNA

• DNA forms a double helix structure.
• The DNA model was proposed by Watson and Crick in 1953.
• Hydrogen bonds link paired bases (Adenine-Thymine, Guanine-Cytosine).
• Hydrophobic bases are located in the inside, hydrophilic sugar-phosphate backbone on the outside.

Complementary Base Pairs

• Adenine (A) pairs with Thymine (T) by two hydrogen bonds.
• Guanine (G) pairs with Cytosine (C) by three hydrogen bonds.

Higher Structure of DNA

• DNA is coiled around histones
• Histones are rich in basic amino acids and attract the acidic DNA.
• Coils form a chain of nucleosomes.
• Nucleosomes form a solenoid structure (six nucleosomes per turn)
• Nucleosomes further condense into chromatin fibers, loops, and minibands for the superstructure.
• This condensation provides a compact form for the chromosomes.

Chromosome & Gene

• DNA molecules have a huge number of nucleotides. RNA molecules have fewer.
• DNA is located in the chromosomes in the nucleus, with each chromosome having a unique type of DNA.
• Humans have 46 chromosomes.
• A gene is part of the DNA responsible for a single protein (1000-2000 nucleotides).

Difference Between DNA & RNA

• DNA has four bases (A, G, C, and T); RNA has four bases (A, G, C, and U).
• DNA's sugar is 2-deoxy-D-ribose; RNA's sugar is D-ribose.
• DNA is usually double-stranded; RNA is single-stranded.
• RNA is typically smaller than DNA.

RNA Molecules

• RNA transmits genetic information needed for cell operation.
• Ribosomal RNA (rRNA) is found in ribosomes, essential for protein synthesis.
• Messenger RNA (mRNA) carries genetic information from DNA to ribosomes (formed through transcription); important in protein synthesis.
• Transfer RNA (tRNA) is the smallest RNA, converting mRNA's genetic information into amino acids for protein synthesis.

Functions of DNA

• DNA replicates itself during cell division.
• It provides the information to create RNA, proteins, and enzymes.

Replication

• DNA separates into two original strands.
• Two new daughter strands are formed using the original strands as templates.
• Replication occurs by breaking hydrogen bonds.
• Replication is bidirectional(occurs in both directions).
• Replication is semiconservative (each new molecule has one original strand and one newly synthesized strand).
• Replication occurs in several places along the helix simultaneously.

Replication (Mechanism)

• Enzymes involved:
  • Helicase: unwinds DNA double helix.
  • Primase: synthesizes primers needed for strand duplication.
  • DNA polymerase: joins nucleotides to build new strands.
  • Ligase: joins Okazaki fragments on the lagging strand.

Protein Synthesis

• Gene expression is the activation of a gene to produce a specific protein.
• The base sequence of a gene determines a particular protein's creation.
• Only a small percentage of DNA contains genes.

Gene Expression

• Transcription
  • mRNA is synthesized
• Translation
  • mRNA directs amino acid sequence.

Transcription

• DNA's genetic information is copied to make mRNA.
• Starts when the DNA segment unwinds.
• DNA polymerase initiates mRNA synthesis.
• The DNA splits into two strands.
• Template strand is used to create RNA.
• Information strand(coding) is not used.
• Transcription runs from 3' to 5' end of the template.
• mRNA is released once complete, and DNA reforms.
• A pairs with U (instead of T).
• Polymerase moves along DNA forming base bonds

Transcription (Sample Problem)

• Given a template strand of DNA, determine the mRNA and informational strand sequences.

Translation

• mRNA carrying genetic information leaves the nucleus and enters the ribosomes.
• tRNA converts the information into amino acids.
• Amino acids are arranged in the proper order.
• Protein synthesis occurs.

Genetic Code

• Language that relates mRNA nucleotides to their corresponding amino acids.
• The mRNA nucleotide sequence determines the order of amino acids.
• Codons
  • Groups of three bases on mRNA.
  • Each codon corresponds to a particular amino acid.
  • All 20 amino acids have codons.
• UGA, UAA, and UAG are stop signals, signaling the end of protein synthesis
• AUG signals the start and codes for methionine (Met)

tRNA (Transfer RNA)

• tRNA translates codons into specific amino acids.
• Contains 70-90 nucleotides.
• The end called the acceptor stem always has the nucleotide ACC and a free OH group binding to a specific amino acid.
• Anticodon
  • Sequence of three nucleotides on tRNA.
  • Complementary to three bases on mRNA.
  • Helps tRNA identify the needed amino acid

Translation (Further Details)

• mRNA attaches to ribosome's small subunit.
• tRNA molecules bring specific amino acids to the mRNA.
• Amino acids create peptide bonds.
• Ribosome moves along mRNA until the end of the codon (translocation).
• Polypeptide chain is released, becoming an active protein
• Sometimes several ribosomes (polysomes) translate the same strand of mRNA simultaneously.

Termination

• Ribosome encounters stop codon (UAA, UAG, or UGA).
• No tRNA complements these signal codons.
• Enzyme releases the completed polypeptide chain (now an active protein).

Translation Stages

• Initiation: mRNA binds to ribosome small subunit
• Elongation: tRNA brings amino acids to the growing chain; peptide bonds form
• Termination: ribosome encounters a stop codon; polypeptide is released

Mutation

• Heritable change to a DNA nucleotide sequence.
• Changes the amino acid sequence, which affects protein structure and function.
• Can affect enzyme function or be random events.
• Example causes: X-rays, overexposure to UV light, chemicals (mutagens), or viruses.

Effect of Mutations

• Somatic cells (non-reproductive)
  • Mutations are limited to that cell and its progeny.
• Germ cells (reproductive)
  • Mutations in germ cells affect the organism and all future generations.

Types of Mutations

• Point mutation
  • Replacement of one base.
  • Alters a single amino acid.
• Frameshift mutation
  • Addition or deletion of one or more bases.
  • Causes a change in the reading frame (codon sequence).
  • Altering most amino acids that follow.

Point Mutation (Examples)

• Single amino acid substitutions can cause conditions like sickle cell anemia.

Silent Mutation

• The resulting amino acid remains unchanged.
• Has little or no effect on the organism

Recombinant DNA

• Synthetic DNA composed of segments from various sources
• Key elements:
  • Host DNA molecule
  • Enzyme to cut DNA.
  • Gene from a second source organism

Recombinant DNA - Process

• Plasmid DNA from bacteria is cut by a restriction enzyme.
• Human DNA is also cut with the same enzyme.
• Sticky ends allow for combination of human and plasmid DNA.
• DNA ligase joins the pieces of DNA.
• Forms recombinant DNA.

Recombinant DNA Technology

• Introduction of human gene of interest into bacterial cells
• Recombinant bacteria multiplied and produce the human protein.

Recombinant Applications & Products

• Production of human medicines (ex: insulin)
• Genetically altered organisms (e.g., Bt crops).
• Antisense RNA (e.g., altering gene expression)

Polymerase Chain Reaction (PCR)

• Technique amplifying a portion of a DNA molecule.
• Key Elements:
  • Target DNA segment
  • Primers (short DNA sequences)
  • DNA polymerase enzyme
  • Nucleotide building blocks (A, T, C, G)
• Process
  • Heat DNA to unwind into single strands
  • Cool to allow complementary primers to anneal.
  • Elevated temperatures allow DNA polymerase to build the complementary strands. -Repeated to exponentially amplify the DNA segment.

DNA Fingerprinting

• DNA molecules from individuals are unique.
• Used as an identification means.
  • DNA extracted and amplified using PCR.
  • DNA is cut into fragments using restriction enzymes.
  • DNA fragments are separated by size using electrophoresis.
  • visualised on an X-ray film; each band corresponding to a DNA segment.

PCR Applications

• Prenatal testing, pathogen detection, genetically modified organism analysis, and liquid biopsies

Test your knowledge on nucleic acids, including DNA and RNA, their structures, and functions. This quiz covers key concepts such as nucleotides, glycosidic bonds, and nucleosides derived from pyrimidine bases. Perfect for biology students seeking to reinforce their understanding of molecular biology.