Chromosomes and DNA Replication 12-2 Biology Ms. Haut

Copyright Pearson Prentice Hall 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 DNA and Chromosomes Many eukaryotes have 1000 times the amount of DNA as prokaryotes. Eukaryotic DNA is located in the cell nucleus inside chromosomes. The number of chromosomes varies widely from one species to the next.

Dog Karyotype Pig Karyotype Humans have: 44 autosomes 2 sex chromosomes 46 total

DNA and Chromosomes Chromosome Structure –Eukaryotic chromosomes contain DNA and protein, chromatin. –DNA tightly coils around proteins called histones. –DNA and histones form nucleosomes. –Nucleosomes pack together, forming a thick fiber. Copyright Pearson Prentice Hall

DNA Replication Each strand of the DNA double helix has all the information needed to reconstruct the other half by the mechanism of base pairing. What is the complementary strand for the following DNA sequence? T A C G G A T T G A A G A T G C C T A A C T T C

DNA Replication In most prokaryotes, DNA replication begins at a single point and continues in two directions. Copyright Pearson Prentice Hall batcerial-chromosomes.jpg

DNA Replication In eukaryotic chromosomes, DNA replication occurs at hundreds of places (origins of replication). Replication proceeds in both directions until each chromosome is completely copied. Speeds up the time it takes to copy the DNA. Copyright Pearson Prentice Hall From Essential Biology with Physiology, 2 ed. By Campbell, Reece.

Copyright Pearson Prentice Hall DNA Replication Duplicating DNA –Before a cell divides, it duplicates its DNA in a process called replication. –Replication ensures that each resulting cell will have a complete set of DNA.

DNA Replication DNA molecule separates into two strands Two new complementary strands following the rules of base pairing are made. Each strand of the double helix of DNA serves as a template for the new strand. Copyright Pearson Prentice Hall

DNA Replication DNA replication depends on specific base pairing –DNA replication Starts with the separation of DNA strands –Then enzymes use each strand as a template To assemble new nucleotides into complementary strands

DNA Replication DNA replication is carried out by DNA helicase that “unzips” the molecule of DNA. Hydrogen bonds between base pairs are broken and the two strands of DNA unwind. Copyright Pearson Prentice Hall DNA helicase

Copyright Pearson Prentice Hall DNA Replication DNA polymerase joins complementary nucleotides to produce a DNA molecule and then “proofreads” each new DNA strand. Copyright Pearson Prentice Hall

DNA Replication

Copyright Pearson Prentice Hall In prokaryotic cells, DNA is found in the a)cytoplasm. b)nucleus. c)ribosome. d)cell membrane.

Copyright Pearson Prentice Hall The first step in DNA replication is a)producing two new strands. b)separating the strands. c)producing DNA polymerase. d)correctly pairing bases. What enzyme separates the 2 strands of DNA? DNA helicase How does helicase separate the strands? by breaking the hydrogen bonds

Copyright Pearson Prentice Hall A DNA molecule separates, and the sequence GCGAATTCG occurs in one strand. What is the base sequence on the other strand? a)GCGAATTCG b)CGCTTAAGC c)TATCCGGAT d)GATGGCCAG

Copyright Pearson Prentice Hall In addition to carrying out the replication of DNA, the enzyme DNA polymerase also functions to a)unzip the DNA molecule. b)regulate the time copying occurs in the cell cycle. c)“proofread” the new copies to minimize the number of mistakes. d)wrap the new strands onto histone proteins.

Copyright Pearson Prentice Hall The structure that may play a role in regulating how genes are “read” to make a protein is the a)coil. b)histone. c)nucleosome. d)chromatin.