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Questions and Answers
What carries hereditary information?
Chromosomes
Which bases form 2 hydrogen bonds?
Which bases are purines?
The sequence of nucleotides in a gene determines the amino acid sequence in a protein.
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What is the primary structure formed by DNA?
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What are transposable elements?
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Which of the following structures protect the ends of chromosomes?
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The noncoding regions inside a gene are called ______ and the coding regions are called ______.
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What is the primary function of regulatory DNA sequences?
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All human chromosomes are identical.
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Match the following structures with their functions:
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Study Notes
Genes and Heredity
- Genes hold instructions defining species traits.
- Hereditary information is encoded on chromosomes.
- Chromosomes are composed of DNA and protein in equal amounts.
- DNA strands run antiparallel with 5' phosphate and 3' hydroxyl ends.
- Adenine (A) pairs with Thymine (T) through 2 hydrogen bonds.
- Cytosine (C) pairs with Guanine (G) through 3 hydrogen bonds.
- Purines (A & G) are larger with two rings, while pyrimidines (C & T) are smaller with one ring.
- This base pairing ensures consistent width of DNA.
- Phosphodiester bonds link sugars in DNA, connecting the phosphate group of one sugar to the hydroxyl group of the next.
- DNA chains are linear and directional.
- DNA's linear polymer structure, with 4 monomer types, provides a chemical basis for storing genetic information.
- DNA's complementary strands act as templates for replication, ensuring information transmission across generations.
- DNA encodes proteins, with genes containing instructions for protein production.
- The linear sequence of nucleotides in a gene dictates the linear sequence of amino acids in a protein, forming the genetic code.
- The genome encompasses the entire set of RNA molecules and proteins an organism can produce.
Nuclear Structure
- The nuclear envelope consists of two concentric bilayer membranes, punctured by nuclear pores.
- The outer nuclear membrane is continuous with the endoplasmic reticulum (ER).
- The nuclear envelope is supported by the nuclear lamina.
- Each chromosome contains a single long DNA molecule along with proteins that compact the DNA and RNA molecules essential for gene expression, DNA duplication, and repair.
- Chromatin is a complex of DNA and tightly bound proteins.
Chromosomes
- Gametes, non-dividing cells, lack DNA or replicate without a complete cell cycle and lack homologous chromosomes.
- Most human cells have two copies of each chromosome, termed homologous chromosomes.
- Sex chromosomes are non-homologous.
- DNA painting uses short nucleic acid sequences attached to colored probes that bind to complementary sequences on DNA, allowing for chromosome identification.
- Chromosomes can be distinguished by staining them with dyes to create unique banding patterns reflecting chromatin structure and base composition.
- A karyotype is a display of the 46 human chromosomes during mitosis.
Genome Composition
- The genome contains non-coding DNA alongside genes, some of which regulate gene expression.
- Differences in non-coding DNA explain variations in genome size.
- Non-coding DNA contributes significantly to genome size differences between closely related organisms despite similar gene numbers.
- The specific arrangement of the genome into chromosomes varies across eukaryotic species.
- Mobile DNA segments called transposable elements, which integrate into chromosomes over time, constitute half of the chromosomal DNA.
- Introns are non-coding regions within genes, while exons represent coding regions.
- Introns typically make up the majority of a gene.
- Regulatory DNA sequences, scattered over vast nucleotide regions, control gene activation and deactivation.
Cell Cycle and Chromosomal Structure
- During interphase, the cell actively expresses genes, synthesizes proteins, and replicates DNA to produce sister chromatids.
- The M phase occurs after DNA replication is complete.
- During the M phase, the nucleus divides into two daughter nuclei, chromosomes condense, the nuclear envelope breaks down, the mitotic spindle forms, and a complete set of chromosomes is pulled apart by the mitotic spindle.
- The nuclear envelope reforms around each set of chromosomes.
- During interphase, chromatin exists in long threads.
- Three specific DNA sites regulate replication and sister chromatid separation:
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Replication Origin: The starting point of bidirectional DNA duplication. Eukaryotes have multiple origins to accelerate replication.
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Centromere: Enables sister chromatids to move into daughter cells. Kinetochores form on centromeres and allow the mitotic spindle to pull sister chromatids apart.
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Telomeres: Located at chromosome ends, these sequences facilitate the replication of chromosome termini and protect them from being misinterpreted as broken DNA.
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- In budding yeast, these sites are short.
- While telomere sequences for eukaryotes are short, centromeres and replication origins are long and complex.
- The specific sequence coding for centromeres is not well-defined.
- Interphase chromosomes decondense and recondense to allow gene expression, DNA replication, and other processes.
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