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Questions and Answers
What is the process called when two strands of DNA separate?
What is the process called when two strands of DNA separate?
Which enzyme is primarily responsible for unwinding the DNA strands during replication?
Which enzyme is primarily responsible for unwinding the DNA strands during replication?
What are the coding regions of genes in eukaryotes called?
What are the coding regions of genes in eukaryotes called?
What term defines the entire DNA contained in an organism or cell?
What term defines the entire DNA contained in an organism or cell?
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What are the small sections of DNA that provide structural organization in the form of nucleosomes?
What are the small sections of DNA that provide structural organization in the form of nucleosomes?
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What is the temperature referred to as when 50% of the DNA molecule is denatured?
What is the temperature referred to as when 50% of the DNA molecule is denatured?
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Which of the following statements about chromatin is true?
Which of the following statements about chromatin is true?
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How many base pairs of DNA does each nucleosome consist of?
How many base pairs of DNA does each nucleosome consist of?
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What type of bond links nucleotides in DNA?
What type of bond links nucleotides in DNA?
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Where is DNA found in prokaryotic cells?
Where is DNA found in prokaryotic cells?
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How many nucleotide pairs are in one turn of the DNA helix?
How many nucleotide pairs are in one turn of the DNA helix?
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Which structures are formed by the hydrogen bonding between bases in DNA?
Which structures are formed by the hydrogen bonding between bases in DNA?
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What does Chargaff's rule state about the concentration of bases in DNA?
What does Chargaff's rule state about the concentration of bases in DNA?
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Which form of DNA is considered the dominant form under physiological conditions?
Which form of DNA is considered the dominant form under physiological conditions?
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What is the distance between adjacent nucleotide pairs in DNA?
What is the distance between adjacent nucleotide pairs in DNA?
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DNA strands run in what orientation to each other?
DNA strands run in what orientation to each other?
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Which statement about nucleosomes is NOT true?
Which statement about nucleosomes is NOT true?
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Which statement about tRNA is NOT true?
Which statement about tRNA is NOT true?
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The phosphate group in nucleic acids is attached to which Carbon of the sugar?
The phosphate group in nucleic acids is attached to which Carbon of the sugar?
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Which sequence is the complementary DNA strand to AGTCCG?
Which sequence is the complementary DNA strand to AGTCCG?
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Which biomolecule has both catalytic activity and the ability to store genetic information?
Which biomolecule has both catalytic activity and the ability to store genetic information?
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Which nucleotide is NOT involved in RNA structure?
Which nucleotide is NOT involved in RNA structure?
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Uric acid is the end product of the metabolism of which base?
Uric acid is the end product of the metabolism of which base?
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What sugar is present in the structure of thymidylic acid?
What sugar is present in the structure of thymidylic acid?
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What is the function of histone acetylation in gene expression?
What is the function of histone acetylation in gene expression?
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Which of the following best describes the role of tRNA?
Which of the following best describes the role of tRNA?
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What is the approximate length of DNA in a human cell when wound around histones?
What is the approximate length of DNA in a human cell when wound around histones?
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What modification occurs during histone acetylation?
What modification occurs during histone acetylation?
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Which type of RNA is more stable in eukaryotic cells than in prokaryotic cells?
Which type of RNA is more stable in eukaryotic cells than in prokaryotic cells?
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How many different tRNA molecules are typically needed for protein synthesis?
How many different tRNA molecules are typically needed for protein synthesis?
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What structure at the 5' end of eukaryotic mRNA protects it from nuclease attack?
What structure at the 5' end of eukaryotic mRNA protects it from nuclease attack?
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What is the role of histone deacetylases in cancer cells?
What is the role of histone deacetylases in cancer cells?
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The sugar in nucleosides is attached to the purine by how many nitrogen atoms?
The sugar in nucleosides is attached to the purine by how many nitrogen atoms?
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Which statement about the B-form of DNA is false?
Which statement about the B-form of DNA is false?
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7-Methylguanosine at the 5' end is primarily present in which type of RNA?
7-Methylguanosine at the 5' end is primarily present in which type of RNA?
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Which statement best describes introns?
Which statement best describes introns?
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Nucleic acids are formed of nucleotides that are linked together with which type of bond?
Nucleic acids are formed of nucleotides that are linked together with which type of bond?
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What is the enzyme responsible for the formation of cAMP?
What is the enzyme responsible for the formation of cAMP?
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If the cytosine content of a double-stranded DNA is 20% of the total bases, what is the thymine content?
If the cytosine content of a double-stranded DNA is 20% of the total bases, what is the thymine content?
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Which type of DNA is known to be left-handed?
Which type of DNA is known to be left-handed?
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Study Notes
DNA: The Molecule of Heredity
- DNA is a polymer of deoxyribonucleotides linked by 3'-5' phosphodiester bonds.
- It's found in both eukaryotic and prokaryotic cells.
- Eukaryotic cells have DNA in the nucleus, mitochondria, and chloroplasts of plants.
- Prokaryotic cells have a single chromosomal DNA and non-chromosomal DNA called "plasmid."
- DNA can be double-stranded linear (nuclear DNA), double-stranded circular (mtDNA, bacterial chromosomal DNA, plasmids, and some viruses), or single-stranded circular or linear (some small viruses).
Structure of DNA
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Primary structure: the linear sequence of nucleotides.
- DNA forms a double helix with two strands held together by complementary base pairing (A with T, C with G).
- The sugar-phosphate backbone is formed by alternating sugar and phosphate units.
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Secondary structure: interactions between bases through hydrogen bonds to form the DNA double helix.
- The two strands of DNA are antiparallel.
- Base pairing is held together by hydrogen bonds: two bonds between A & T, three bonds between C & G.
- Hydrophobic interactions between adjacent base pairs provide stability to the double helix.
- Each turn of the double helix consists of 10.4 nucleotide pairs, measuring 3.4 nm. The distance between adjacent base pairs is 0.34 nm.
- The double helix structure creates major and minor grooves.
- Chargaff's rules: the concentration of adenine (A) equals thymine (T), and the concentration of cytosine (C) equals guanine (G).
Types and Forms of DNA
Conformation of DNA
- The conformation of DNA is influenced by base composition, physical conditions (salt concentration, temperature), and the presence of specific proteins.
- B-form: the dominant DNA conformation under physiological conditions (low salt concentration), described by Watson and Crick.
- Z-DNA: produced experimentally, contains a single groove.
- A-DNA and Z-DNA: present in high salt concentration or in the presence of alcohol.
Denaturation (Melting)
- The separation of the two strands of DNA.
- Can be achieved by enzymes like helicase, increasing temperature, or adding alkalis (decreasing salt concentration).
- Melting temperature (Tm): the temperature required to denature 50% of a DNA molecule.
- Annealing (renaturation): reforming of the DNA double helix by cooling thermally melted DNA.
- Hybridization: rejoining between DNA strands, either with other DNA, RNA, or a probe.
Genes: Arrangement of DNA
- A gene is a functional and physical unit of heredity, passed from parents to offspring.
- A segment of DNA that codes for a single protein.
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Eukaryotic genes consist of:
- Coding regions (exons): code for protein sequences.
- Non-coding regions (introns): removed during RNA processing.
- Regulatory sequences: control when, where, and how much protein is produced.
Genome & Chromosomes
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Genome: the complete DNA content of an organism or cell.
- Humans have 23 pairs of chromosomes: 22 autosomes and 1 pair of sex chromosomes.
- Mitochondria contain a small amount of DNA.
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Chromosomes: linear pieces of DNA containing many genes.
- Chromosomes are too fine and tangled in non-dividing cells, referred to as chromatin.
- During mitosis, they become more condensed and visible, referred to as chromatids.
Chromatin or Chromatid
- Complex of DNA and protein.
- Contains histones and non-histone proteins.
- Non-histone proteins are involved in transcription, replication, and DNA repair.
- Histones are proteins that bind closely to DNA molecules and are responsible for chromatin structure and gene regulation.
- Histones are rich in positively charged amino acids (lysine) which interact with negatively charged phosphate groups in the DNA helix, forming nucleosomes.
Types of Histones
- Linker histones (H1 or H5): connect nucleosomes.
- Core histones (H2A, H2B, H3, H4): associate with DNA to form nucleosomes, forming a complex with 146 base pairs of DNA.
Nucleosomes: Packing of Chromatin
- Each nucleosome consists of 146 base pairs of DNA wrapped around a histone core (two copies of each core histone).
- The DNA wraps around the histone core twice per nucleosome.
- Linker DNA (50 base pairs) connects two nucleosomes.
- Without histones, human DNA would be 1.8 meters, but when wound on histones, it is only 0.09 mm.
- Histone acetylation can affect gene expression:
- Neutralizes positively charged lysine R groups, decreasing binding force between histones and DNA.
- This allows chromatin expansion, permitting transcription (transcriptionally active).
Histone Acetylation: Acetylases vs. Deacetylases
- Histone acetylation is an important mechanism in gene regulation.
- Acetylation neutralizes the positive charges on histones, reducing their binding to DNA.
- Hyperacetylated chromatin is transcriptionally active, increasing gene expression.
- Cancer cells have high levels of histone deacetylases, which increase replication.
RNA: Ribonucleic Acid
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tRNA (transfer RNA): 10-15% of total RNA.
- There are over 20 different tRNA molecules (75-95 nucleotides).
- They have a similar structure across all organisms.
- Functions as a carrier of amino acids to the site of protein synthesis.
- At least one tRNA molecule exists for each of the 20 amino acids used in protein synthesis.
- Eukaryotic tRNA is less stable than prokaryotic tRNA.
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mRNA (messenger RNA): 1-5% of total RNA.
- Single-stranded linear molecules.
- Eukaryotic mRNA is more stable than prokaryotic mRNA.
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Eukaryotic mRNA features:
- 5' cap (methylated GTP) protects it from nuclease attack.
- 3' poly-A tail protects it from nuclease attack.
- Prokaryotes have a Shine-Dalgarno sequence at the 5' end of mRNA, which helps in ribosome attachment during protein synthesis.
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mRNA functions:
- Carries genetic information from the nucleus to the cytoplasm.
- Contains genetic information in the form of genetic code.
- May contain information for forming more than one protein.
Additional Information
- The most stable form of DNA under physiological conditions is the B-form.
- Histones are present in all living organisms, except bacteria and some algae.
- Histone acetylation is a crucial mechanism for regulating gene expression.
- Eukaryotic cells have both coding (exons) and non-coding (introns) regions in their genes.
- The genome contains all the DNA in an organism or cell.
- Chromatin is the less condensed form of DNA found in non-dividing cells, while chromatid is the more condensed form found during mitosis.
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Description
Explore the fascinating structure and function of DNA in this quiz. Learn about the differences between eukaryotic and prokaryotic cells, as well as the various forms and structures of DNA. Test your knowledge on the primary and secondary structures of DNA and their significance in heredity.
