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Questions and Answers
What primarily makes up a gene?
What primarily makes up a gene?
What is the main role of nucleosomes in the cell?
What is the main role of nucleosomes in the cell?
How does chromatin affect gene expression?
How does chromatin affect gene expression?
What structure holds two identical parts of a chromosome together?
What structure holds two identical parts of a chromosome together?
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What is the immediate product of DNA transcription?
What is the immediate product of DNA transcription?
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What type of chromatin is characterized by being transcriptionally inactive?
What type of chromatin is characterized by being transcriptionally inactive?
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Which proteins primarily assist in DNA packing into chromatin?
Which proteins primarily assist in DNA packing into chromatin?
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What affects how many proteins are synthesized from a given gene?
What affects how many proteins are synthesized from a given gene?
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What is the primary function of RNA in relation to DNA?
What is the primary function of RNA in relation to DNA?
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Which of the following describes the flow of genetic information as stated in the Central Dogma of Molecular Biology?
Which of the following describes the flow of genetic information as stated in the Central Dogma of Molecular Biology?
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During transcription, which molecule is synthesized from a DNA template?
During transcription, which molecule is synthesized from a DNA template?
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Which nucleotide sugar is found in RNA but not in DNA?
Which nucleotide sugar is found in RNA but not in DNA?
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What structure do purine nitrogen bases have?
What structure do purine nitrogen bases have?
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Which function is NOT associated with nucleotides in cells?
Which function is NOT associated with nucleotides in cells?
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Which describes the role of DNA during DNA replication?
Which describes the role of DNA during DNA replication?
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What is the significance of Chargaff's rules in understanding DNA structure?
What is the significance of Chargaff's rules in understanding DNA structure?
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What is the primary function of messenger RNA (mRNA) in the protein synthesis process?
What is the primary function of messenger RNA (mRNA) in the protein synthesis process?
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Which component of RNA is different from DNA?
Which component of RNA is different from DNA?
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What role do antioxidants play in relation to DNA stability?
What role do antioxidants play in relation to DNA stability?
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Which type of RNA is primarily responsible for bringing amino acids to the ribosome?
Which type of RNA is primarily responsible for bringing amino acids to the ribosome?
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Which of the following statements is true regarding ribosomal RNA (rRNA)?
Which of the following statements is true regarding ribosomal RNA (rRNA)?
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What effect does oxidative damage have on DNA?
What effect does oxidative damage have on DNA?
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Which type of RNA functions in RNA silencing and regulation of gene expression?
Which type of RNA functions in RNA silencing and regulation of gene expression?
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What distinguishes the structure of transfer RNA (tRNA) from other types of RNA?
What distinguishes the structure of transfer RNA (tRNA) from other types of RNA?
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Study Notes
Genes
- Genes are the basic unit of heredity
- Genes are made up of DNA
- Genes provide instructions for making molecules called proteins
- Every person inherits two copies of each gene, one from each parent
Chromosomes
- Chromosomes are thread-like structures found in the nucleus of cells
- They contain DNA, histones, and other proteins which affect gene expression
- Chromosomes are not visible under a microscope unless the cell is dividing
DNA-Protein Complexes
- DNA complexes with specific DNA binding proteins to form chromatin
- Histones are important DNA binding proteins
- Histones are small, positively charged, arginine-lysine rich proteins
- DNA supercoils around aggregated histones
Chromosomes, Chromatid, Chromatin
- Each chromosome is made up of two identical parts called chromatids
- Two chromatids are linked together at the centromere
- Chromatin consists of histones and DNA
- 147 base pairs of DNA wrap around 8 core histones to form the nucleosome, the basic unit of chromatin
Nucleosome
- The nucleosome core contains 8 histones
- DNA is wrapped twice around the nucleosome core
- A linker histone holds the nucleosome together
- A linker DNA sequence extends from one nucleosome to the next
Nucleosome Functions
- Nucleosomes help to supercoil DNA, which is essential for:
- Packing genetic material into the nucleus
- Organizing DNA for cell division
- Controlling DNA expression, as supercoiled DNA cannot be transcribed
- Cells can specialize by permanently supercoiling DNA (heterochromatin)
- The associated histones can promote or inhibit transcription of active chromatin (Euchromatin)
Applications of Nucleic Acids
- Relationship testing (DNA Paternity)
- Diagnostics, including identification of viral STDs
Nucleic Acids
- The two main nucleic acids are deoxyribonucleic acid (DNA) and ribonucleic acid (RNA)
- Nucleic acids record and transmit genetic information
- They determine the structure and function of the body through proteins and enzymes
- They pass information from generation to generation
Central Dogma of Molecular Biology
- The flow of genetic information is from DNA to RNA to Protein
- DNA replication produces copies of the DNA molecule
- Transcription copies DNA into RNA
- Translation uses RNA to create proteins
- Gene expression occurs in two steps:
- DNA is transcribed to RNA
- RNA is translated into protein
Structures and Functions of DNA and RNA
- Both DNA and RNA are polymers (polynucleotides)
- The monomer unit of a nucleic acid is a nucleotide
Components of a Nucleotide
- A nucleotide consists of:
- A 5-carbon sugar (pentose): deoxyribose for DNA and ribose for RNA
- A purine or pyrimidine nitrogenous base attached to the sugar
- A phosphate group
Nitrogenous Bases
- Purines have a two-ring structure (Adenine (A) and Guanine (G))
- Pyrimidines have a single-ring structure (Cytosine (C), Thymine (T) in DNA, and Uracil (U) in RNA)
Nucleotide Formation
- Nucleotides are formed by linking a nitrogenous base to a pentose sugar, and then adding a phosphate group
Components of Nucleic Acids
- Nucleoside: A nitrogenous base linked to a pentose sugar
- Nucleotide: A nucleoside linked to a phosphate group
Functions of Nucleotides in Cells
- Precursors of DNA and RNA
- Carriers of chemical energy (ATP and GTP)
- Components of co-factors (NAD+, FAD, Co-enzyme A)
- Components of activated biosynthetic intermediates (UDP-glucose – precursor of glycogen)
- Cellular secondary messengers (cAMP and cGMP)
Nomenclature
- Suffix: ‘osine’ for purine bases, ‘idine’ for pyrimidine bases
- Prefix: ‘deoxy’ for DNA
Base Composition of DNA
- The chemical basis of base pairing in DNA was discovered by Erwin Chargaff in the 1940s
- The four bases do not occur in equal amounts:
- The amounts vary from species to species
- A always pairs with T, and C always pairs with G
Factors Affecting DNA Stability: Chemicals
-
Nitrous acid (deaminating agent)
- Precursors (Nitrate and nitrite salts)
- Found in preservatives
-
Bisulphite
- Found in preservatives
Factors Affecting DNA Stability: Oxidative Damage
- Hydrogen peroxide, hydroxyl ions, superoxide radicals can damage DNA
- These arise during irradiation or as a byproduct of aerobic metabolism
- Most damage is done by OH- ions
- Human cells are subjected to thousands of damaging oxidative reactions
- Oxidative damage has implications for cancer
- Antioxidants can help protect against oxidative damage (Vitamins A, C, and E; minerals copper, zinc, and selenium)
RNA: Ribonucleic Acid
- Chemically, RNA is very similar to DNA. Key differences include:
- RNA uses ribose instead of deoxyribose
- RNA uses uracil (U) instead of thymine (T), with U being complementary to A
- RNA tends to be single-stranded
- RNA has many functions, while DNA has a single function
- Types of RNA: mRNA, tRNA, rRNA
RNA Structure: Messenger RNA (mRNA)
- mRNA is synthesized during transcription
- The sequence of bases in DNA is copied into mRNA with a complementary base sequence
- mRNA varies greatly in molecular weight and base sequence
- Total cellular mRNA составляет 5%
tRNA Structure
- Small molecules that carry specific amino acids during protein synthesis
- Have a clover leaf structure
- Total cellular tRNA составляет 15%
- There are at least 20 types of tRNA in a cell
- tRNA recognizes and reads the codon of the mRNA to fetch the correct amino acid
- Delivers the amino acid to the growing polypeptide chain at the ribosomal site
RNA: Ribosomal RNA (rRNA) & Other RNAs
-
Ribosomal RNA (rRNA)
- Most abundant type of RNA
- Forms part of the site for protein synthesis
- Total cellular rRNA составляет 80%
-
Other RNAs
-
Small nuclear RNA (snRNA) 2%
- Involved in post-transcriptional modification of proteins
-
microRNA (miRNA)
- Functions in RNA silencing and post-transcriptional regulation of gene expression
-
Small interfering RNA (siRNA)
- Interferes with the expression of specific genes
-
Small nuclear RNA (snRNA) 2%
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