12-2 Chromosomes and DNA Replication Photo credit: Jacob Halaska/Index Stock Imagery, Inc. Copyright Pearson Prentice Hall
Copyright Pearson Prentice Hall DNA and Chromosomes DNA and Chromosomes In prokaryotic cells, DNA is located in the cytoplasm. Most prokaryotes have a single DNA molecule containing nearly all of the cell’s genetic information. Copyright Pearson Prentice Hall
Copyright Pearson Prentice Hall DNA and Chromosomes Chromosome Structure Eukaryotic chromosomes contain DNA and protein, tightly packed together to form chromatin. Chromatin consists of DNA tightly coiled around proteins called histones. Copyright Pearson Prentice Hall
Copyright Pearson Prentice Hall DNA and Chromosomes Eukaryotic Chromosome Structure Chromosome Nucleosome DNA double helix Coils Supercoils Eukaryotic chromosomes contain DNA wrapped around proteins called histones. The strands of nucleosomes are tightly coiled and supercoiled to form chromosomes. Histones Copyright Pearson Prentice Hall
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Human Evolution - Hominoid Chromosomes Comparing bullet marks: “Numerous studies show that CHROMOSOME SIMILARITY is a good measure of GENETIC RELATEDNESS. The probability that two different chromosomes would independently have identical banding patterns by chance is essentially zero.” “Detailed studies provide clear evidence that any IDENTICAL CHROMOSOMES in two different species INDICATES COMMON ANCESTRY just as surely as identical scratch patterns on two bullets indicate that both came from the same gun.” (Wallace, 1966).
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Copyright Pearson Prentice Hall DNA Replication DNA Replication The sites where separation and replication occur are called replication forks. Copyright Pearson Prentice Hall
Copyright Pearson Prentice Hall DNA Replication DNA Replication: The DNA molecule separates into two strands, then produces two new complementary strands following the rules of base pairing. Each strand of the double helix of DNA serves as a template for the new strand. Copyright Pearson Prentice Hall
Copyright Pearson Prentice Hall DNA Replication New Strand Original strand Nitrogen Bases Growth Growth During DNA replication, the DNA molecule produces two new complementary strands. Each strand of the double helix of DNA serves as a template for the new strand. Replication Fork Replication Fork DNA Polymerase Copyright Pearson Prentice Hall
Copyright Pearson Prentice Hall DNA Replication How Replication Occurs DNA replication is carried out by enzymes that “unzip” a molecule of DNA. Hydrogen bonds between base pairs are broken and the two strands of DNA unwind. Copyright Pearson Prentice Hall
Copyright Pearson Prentice Hall DNA Replication The principal enzyme involved in DNA replication is DNA polymerase. DNA polymerase joins individual nucleotides to produce a DNA molecule and then “proofreads” each new DNA strand. Copyright Pearson Prentice Hall
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Copyright Pearson Prentice Hall 12–2 In prokaryotic cells, DNA is found in the cytoplasm. nucleus. ribosome. cell membrane. Copyright Pearson Prentice Hall
Copyright Pearson Prentice Hall 12–2 The first step in DNA replication is producing two new strands. separating the strands. condensing the DNA. correctly pairing bases. Copyright Pearson Prentice Hall
Copyright Pearson Prentice Hall 12–2 A DNA molecule separates, and the sequence GCGAATTCG occurs in one strand. What is the base sequence on the other strand? GCGAATTCG CGCTTAAGC TATCCGGAT GATGGCCAG Copyright Pearson Prentice Hall
Copyright Pearson Prentice Hall 12–2 In addition to carrying out the replication of DNA, the enzyme DNA polymerase also functions to unzip the DNA molecule. regulate the time copying occurs in the cell cycle. “proofread” the new copies to minimize the number of mistakes. wrap the new strands onto histone proteins. Copyright Pearson Prentice Hall
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