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Questions and Answers
What type of interactions stabilize the double helix structure of DNA?
What type of interactions stabilize the double helix structure of DNA?
How many base pairs are present in each complete turn of the DNA double helix?
How many base pairs are present in each complete turn of the DNA double helix?
Which groove in the DNA double helix is wider and provides better access for protein binding?
Which groove in the DNA double helix is wider and provides better access for protein binding?
What is the reason for G-C base pairs being more stable than A-T base pairs?
What is the reason for G-C base pairs being more stable than A-T base pairs?
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Which of the following correctly describes the structure of eukaryotic nuclear chromosomes?
Which of the following correctly describes the structure of eukaryotic nuclear chromosomes?
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What is the primary role of histones in the context of chromatin structure?
What is the primary role of histones in the context of chromatin structure?
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Which of the following modifications to histones is associated with changes in chromatin function?
Which of the following modifications to histones is associated with changes in chromatin function?
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What component forms the core of a nucleosome?
What component forms the core of a nucleosome?
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Which type of histone is specifically linked to the protection of linker DNA from exonuclease digestion?
Which type of histone is specifically linked to the protection of linker DNA from exonuclease digestion?
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How does chromatin appear when viewed using electron microscopy?
How does chromatin appear when viewed using electron microscopy?
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Which type of DNA is primarily responsible for encoding functional proteins in eukaryotic cells?
Which type of DNA is primarily responsible for encoding functional proteins in eukaryotic cells?
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What is the main difference between ribose and deoxyribose sugars?
What is the main difference between ribose and deoxyribose sugars?
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In DNA structure, what type of bonds link nucleotides together in a strand?
In DNA structure, what type of bonds link nucleotides together in a strand?
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Which nitrogenous base is unique to RNA?
Which nitrogenous base is unique to RNA?
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What characterizes the antiparallel arrangement of DNA strands?
What characterizes the antiparallel arrangement of DNA strands?
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In which cellular organelle is mitochondrial DNA primarily located?
In which cellular organelle is mitochondrial DNA primarily located?
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What links the nitrogenous base to the sugar in a nucleoside?
What links the nitrogenous base to the sugar in a nucleoside?
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Which part of the nucleotide structure is responsible for key energy transfer functions?
Which part of the nucleotide structure is responsible for key energy transfer functions?
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What is the primary characteristic of Z-DNA compared to A-DNA and B-DNA?
What is the primary characteristic of Z-DNA compared to A-DNA and B-DNA?
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How does the melting temperature (Tm) of DNA depend on its base composition?
How does the melting temperature (Tm) of DNA depend on its base composition?
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Which factor does NOT directly contribute to DNA denaturation?
Which factor does NOT directly contribute to DNA denaturation?
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What is the rise per base pair in B-DNA?
What is the rise per base pair in B-DNA?
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What is the characteristic of the minor groove in A-DNA?
What is the characteristic of the minor groove in A-DNA?
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Which of the following statements about the centromere is accurate?
Which of the following statements about the centromere is accurate?
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How many residues (base pairs) are present per turn in Z-DNA?
How many residues (base pairs) are present per turn in Z-DNA?
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What is often measured at 260 nm to assess single-stranded DNA?
What is often measured at 260 nm to assess single-stranded DNA?
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Study Notes
Nucleotide Chemistry
- Nucleic acids are essential for storing and expressing genetic information. DNA (Deoxyribonucleic acid) and RNA (Ribonucleic acid) are included.
- DNA carries the complete genetic information of an individual.
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Eukaryotic cells: DNA is primarily located in the nucleus found in chromosomes and a smaller amount is in the mitochondria.
- Nuclear DNA contains the genetic information for functional proteins and RNAs.
- Mitochondrial DNA holds genes encoding proteins within the electron transport chain, transfer RNA (tRNA), and ribosomal RNA (rRNA) subunits.
- Prokaryotic cells: These cells possess a single chromosome and may have extra-chromosomal DNA (plasmids), such as in chloroplasts of plants.
DNA Structure
- DNA is composed of two strands.
- These two strands coil around each other in a double helix, a structure described by Watson and Crick.
- Each strand is a polymer made of deoxyribonucleotides.
- The nucleotides are linked together covalently through 3'-5' phosphodiester bonds.
Nucleotide Structure
- A nucleotide has three components:
- Nitrogenous base
- Pentose sugar
- Phosphate
Nitrogenous Bases
- These bases are derivatives of purines and pyrimidines.
- DNA and RNA share the purines adenine (A) and guanine (G).
- Cytosine (C) is present in both DNA and RNA
- Thymine (T) is found exclusively in DNA.
- Uracil (U) is exclusively found in RNA.
Pentoses of Nucleotides
- RNA contains ribose.
- DNA contains 2-deoxyribose.
- The difference between ribose and 2-deoxyribose is the presence of a hydroxyl group (-OH) at the 2' carbon in ribose and a hydrogen atom (H) at the 2' carbon in 2-deoxyribose. This difference affects the secondary structure and stability of RNA versus DNA. RNA is typically less stable.
Nucleoside and Nucleotide
- A nucleoside is formed when a nitrogenous base is linked to a sugar (at the 1' carbon).
- A nucleotide is a nucleoside to which one or more phosphate groups are attached (at the 5' carbon).
- The linking of the base to the sugar is a β-Glycosidic bond.
DNA Primary Structure
- Nucleotides in a DNA strand are linked via phosphodiester bonds.
- These bonds connect the 3' carbon of one sugar to the 5' carbon of the next sugar. The sequence of these linked nucleotides forms the primary structure.
- DNA has two ends, a 5' end (free phosphate group) and a 3' end (free hydroxyl group).
DNA Secondary Structure
- DNA's secondary structure adopts a double helix.
- The two DNA strands run in opposite directions (antiparallel).
- The strands are stabilized by hydrogen bonds between complementary base pairs: adenine (A) with thymine (T), and cytosine (C) with guanine (G).
- The hydrophobic bases stack on top of each other, contributing to the structure's stability and compact form.
- The helical structure includes major and minor grooves providing access for regulatory proteins.
DNA Base Complementarity
- A-T pairs are held together by two hydrogen bonds.
- G-C pairs are held together by three hydrogen bonds.
- The number of purines always equals the number of pyrimidines.
DNA Tertiary Structure
- DNA can exist in different structural forms (e.g., A-DNA, B-DNA, Z-DNA).
- The different forms have varied parameters including helical rotation, base pairs per turn, rise per base pair, and major/minor groove characteristics
- Eukaryotic DNA is generally double-stranded and linear, whereas prokaryotic DNA can be circular
- Other forms, such as mitochondrial DNA, can also be circular.
DNA Denaturation (Melting)
- Denaturation is the separation of the two DNA strands.
- Can be prompted by changes in pH or temperature, disrupting hydrogen bonds between base pairs.
- Melting temperature (Tm) is the temperature at which 50% of the DNA molecules exist as single strands.
- High G-C content correlates to a higher Tm and greater stability due to the extra hydrogen bond.
- Denaturation is monitored via absorbance measurements.
Genetic Terminology
- A typical human somatic cell contains 46 chromosomes arranged in 23 pairs.
- Chromosomes are made up of two identical chromatids attached at the centromere.
- Chromatids are composed of condensed chromatin.
- Chromatin is made up of DNA and associated proteins (histones and non-histones).
- The centromere region is rich in adenine (A) and thymine (T) base pairs and important for the connection of chromosomes to the mitotic spindle during cell division.
DNA Organization (Packing)
- The large length of DNA is organized within cells to allow for replication and gene expression.
- DNA interacts with various proteins to condense into structures like chromatin.
Histones
- Histones are basic proteins that form complexes with DNA, playing a major role in DNA packaging in eukaryotic cells.
- They contain positive charges that attract the negatively charged phosphate groups of DNA, forming ionic bonds.
- There are five types of histones (H1, H2A, H2B, H3, H4).
- Histone modification plays a key role in chromatin structure and in regulating gene expression.
Nucleosome
- A nucleosome is a fundamental structural unit of chromatin.
- It consists of a core of DNA wrapped around an octamer of histone proteins (two each of H2A, H2B, H3, and H4).
- DNA linker regions join nucleosomes together.
- Histone H1 plays a role in compacting the chromatin structure.
Chromatin
- Chromatin is the complex of DNA and proteins that forms chromosomes within the nucleus of eukaryotic cells.
- The structure of chromatin is dynamic and responsive to intracellular signals.
- Chromatin organization can be viewed as "beads on a string" with nucleosomes forming the beads and linker DNA forming the string.
Central Dogma of Biology
- This describes the flow of genetic information: DNA to RNA to protein.
- DNA replication creates identical copies of DNA for cell division.
- DNA is transcribed into RNA molecules.
- RNA is translated into proteins through ribosomes. tRNA molecules carry amino acids to the ribosomes ensuring the correct protein sequence is synthesized.
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Description
Explore the fascinating world of nucleic acids, including DNA and RNA, essential for genetic information storage and expression. Learn about the differences between eukaryotic and prokaryotic cells, as well as the structural characteristics of DNA as described by Watson and Crick.