University:
California State University, Northridge
Course:
CHEM 566 | DNA-Protein Interactions
Academic year:

2007
Views:

440

Pages:

25
Author:

Nathaly Davidson

Chapter 5 Cancer: DNA Synthesis, Mitosis, and Meiosis Why do we care about DNA structure? • Because the structure of DNA allows life as we know it to exist • Because complementary base pairing allows – new cells to be made with exactly the same DNA as the original cell • If you can’t do this, you will die! • A brain cell makes another brain cell, not a liver cell in your head • Because complementary base pairing allows – DNA to make an exactly correct RNA – that then can make an exactly correct protein • People need to make insulin, stomach digestive enzymes, etc • If you can’t do this, you will die! • Because it is Nerdy fun… 2 DNA Replication • The double stranded DNA molecule separates – at hydrogen bonds that hold the complementary bases together • Now we have 2 single strands of DNA that are complementary to each other. – If there is an A on one strand there is a T on the other strand • The enzyme DNA polymerase adds the correct base to the now single strands of DNA – By complementary base pairing • • • • If there is a G, DNA polymerase will add a C If there is a T, DNA polymerase will add an A If there is a C, DNA polymerase will add a G If there is an A, DNA polymerase will add a T 3 DNA Replication • double stranded DNA before replication • double stranded DNA molecule separates • Now we have 2 single strands of DNA that are complementary to each other. • • The enzyme DNA polymerase added the correct base to the two single strands of DNA to create – 2 new double stranded DNA molecules – that are identical to the original double stranded DNA before replication 4 5 DNA Replication • Results in two identical DNA molecules • Each new DNA molecule is half new and half from the old molecule • When an entire chromosome is copied, the two sister chromatids are connected at the centromere • Now the cell is ready to divide 6 DNA Replication 7 5.3 The Cell Cycle and Mitosis • Mitosis is an asexual division • Is part of the cell cycle – the life cycle of the cell • Makes new cells that are exactly the same as the original cells – Liver cells make more Liver cells 8 The Cell Cycle and Mitosis For cells that divide by mitosis, there are 3 steps in the cell cycle: 1. Interphase = • DNA replication 2. Mitosis = • Replicated DNA/chromosomes divide in half 3. Cytokinesis = • cell divides in half 9 The Cell Cycle and Mitosis 10 Interphase • Most of a cell’s life is spent in interphase • Normal functions are carried out – Nerve cells release neurotransmitters – Pancreatic cells make and release insulin • Three stages of interphase: – G1 • Cell growth –S • DNA replication – G2 • Cell growth and prep for division 11 Cell Cycle Copyright © 2007 Pearson Prentice Hall, Inc. 12 Mitosis • The purpose of mitosis is to – separate the sister chromatids – each new cell has a complete set of chromosomes Cytokinesis • The cell itself divides in half creating – two identical daughter cells 13 Cell Cycle 14 Cytokinesis • Animal cells produce a band of filaments that divide the cell in half 15 Cell Cycle Control and Mutation • Cells can commit suicide if problems or mutations occur during the cell cycle – Cell suicide is called Apoptosis • Each stage in the cell cycle is an opportunity for cells to check for mutations or problems – These are called cell cycle Checkpoints • At the checkpoints, Cells determine if they are ready to enter next part of cell cycle – Only proceed if no mutations are detected – If they detect mutations, apoptosis occurs 16 Cell Cycle Control and Mutation 17 Cell Cycle Control and Mutation • If checkpoints exist and cells apoptose when mutated, how can a cancerous cell exist? • If mutations occur in proteins that do the “checking or detecting” of mutations – then mutations can slip through the checkpoints undetected • When the proteins that make the the cell cycle go and stop are mutated and do not work – the cell divides uncontrollably – This results in a tumor – More and more mutations in this uncontrolled dividing tumor cell results in a malignant cell = cancer 18 Cell Cycle Control and Mutation • Mutations in the DNA can produce – – – – nonfunctioning proteins Proteins that do something they normally do not Proteins that do their normal function too much or too fast Uneffected proteins • Mutations can be inherited – Born with the mutations • Mutations can be induced by exposure to carcinogens that damage DNA and chromosomes – Cigarette smoke – Acetone in nail polish remover 19 Cell Cycle Control and Mutation • Cell cycle control genes are called proto-oncogenes proto-: before -onco: cancer • Proto-oncogenes: – Normal genes on many different chromosomes – Regulate cell cycle and cell division • When mutated, they become oncogenes • Oncogenes cause – – – – – the cell cycle to bypass or ignore checkpoints Keep dividing regardless of mutations and problems More and more mutations occur More and more cell divisions occur Bigger and nastier tumors occur 20 Cell Cycle Control and Mutation 21 22 Cell Cycle Control and Mutation • Tumor suppressor genes – stop cell division when necessary • Normal cell that does not need to divide • Mutated cell that needs to apoptose • Tumor suppressor gene mutations cause – the cell cycle to go because there is nothing to stop it – Cells will override the checkpoints – Cells will divide out of control 23 Copyright © 2007 Pearson Prentice Hall, Inc. 24 What Is Cancer? • Benign tumors do not invade surrounding tissue • Malignant tumors invade surrounding structures: – are cancer • Cells from Malignant tumors can break away and start new cancers elsewhere – through the process of metastasis – Benign tumors cannot metastasize 25

Cancer. DNA Synthesis, Mitosis, and Meiosis

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