Presentation is loading. Please wait.

Presentation is loading. Please wait.

Telomeres The leading strand of linear chromosomes can be replicated to the end The lagging strand addition of sequential RNA primers as polymerase moves.

Published bySamuel Clarke Modified over 8 years ago

Similar presentations

Presentation on theme: "Telomeres The leading strand of linear chromosomes can be replicated to the end The lagging strand addition of sequential RNA primers as polymerase moves."— Presentation transcript:

1 Telomeres The leading strand of linear chromosomes can be replicated to the end The lagging strand addition of sequential RNA primers as polymerase moves toward the end of the chromosome – means an RNA primer is left “stranded” 1

2 2 Focusing on what happens at THIS chromosome END (because “upstream” there are Okazaki fragments generated From the fork moving in the opposite direction) This is NOT The chromosome end! (This is NOT a chromosome end)

3 (GGA -OH +PPP- T- OH )GGAT- OH (5’ exonuclease activity) Momentary detour to consider leading strand and its RNA primer… lagging leading

4 Telomeres This problem is resolved by repetitive sequences at the ends of chromosomes, called telomeres These repeats ensure that incomplete chromosome replication does not affect vital genes chromosomes WILL shorten with subsequent cell divisions, but they can shorten a lot before gene structure and expression is affected 4

5 Telomerase Telomeres are synthesized by the ribonucleoprotein telomerase which is active in germ cells Blackburn, Greider, and Szostak received the 2009 Nobel Prize for the discovery of telomeres and telomerase The RNA in telomerase is complementary to the telomere repeat sequence and acts as a template for addition of DNA – creating the long tandem repeats that are expendable for many cell divisions 5

6 6 = Reverse transcriptase (making DNA copy of RNA template) Telomere DNA up to 20kb long – so RNA primer of lagging strand can result in a “short” copy of the strand with no loss of important information

7 Telomeres, Aging, and Cancer Telomere length is important for chromosome stability, cell longevity, and reproductive success Telomerase is active in germ-line cells and some stem cells in eukaryotes Differentiated somatic cells and cells in culture have virtually no telomerase activity; such cells have limited life spans (30 to 50 cell divisions) Cancer cells are often somatic cells in which telomerase activity has been re-activated (so can divide indefinitely) 7

8 Copyright © 2012 Pearson Education Inc. Genetics Analysis: An Integrated Approach 7.5 Molecular Genetic Analytical Methods Make Use of DNA Replication Processes Molecular biologists have used their understanding of DNA replication to develop new methods of molecular analysis Two widely used methods include polymerase chain reaction (PCR) and dideoxynucleotide DNA sequencing 8

9 Copyright © 2012 Pearson Education Inc. Genetics Analysis: An Integrated Approach The Polymerase Chain Reaction The polymerase chain reaction (PCR) is an automated version of DNA replication that produces millions of copies of a short target DNA segment You are carrying out PCRs in lab. You should understand why you need primers, dNTPs, and a heat-stable DNA polymerase for these reactions. Why do you not need helicase, SSB, primase, ligase, sliding clamp? Homework and lab work will test your understanding of PCR (knowledge will be tested on exams) 9

10 Copyright © 2012 Pearson Education Inc. Genetics Analysis: An Integrated Approach Dideoxynucleotide DNA Sequencing The ultimate description of a DNA molecule is its precise sequence of bases The first DNA-sequencing protocols were developed by Maxam and Gilbert, and another by Sanger in 1977 The Sanger (dideoxynucleotide) method was most amenable to automation and is the method of choice today 10

11 Copyright © 2012 Pearson Education Inc. Genetics Analysis: An Integrated Approach 11

12 Copyright © 2012 Pearson Education Inc. Genetics Analysis: An Integrated Approach 12

13 Copyright © 2012 Pearson Education Inc. Genetics Analysis: An Integrated Approach 13 Note: 5’end radioactively labelled primer What would happen if you added no dCTP and only added ddCTP?

14 5’ exonuclease: Recognizes free 5’ phosphate – then cuts adjacent phosphodiester bond Endonuclease: Recognizes base sequence – then cuts phosphodiester bond FREE 5’ phosphate FREE 3’ hydroxyl 3’ exonuclease: Recognizes free 3’ hydroxyl – then cuts adjacent phosphodiester bond Exonucleases vs Endonucleases

15 Hydrolysis of Phosphodiester bond

16 Copyright © 2012 Pearson Education Inc. Genetics Analysis: An Integrated Approach 16

17 Copyright © 2012 Pearson Education Inc. Genetics Analysis: An Integrated Approach Automated DNA Sequencing Automated DNA sequencers use a single reaction for each DNA sequence, in which all four ddNTPs are included Each ddNTP is labeled with a unique fluorescent marker The DNA is synthesized, and a mixture of fragments is produced and run on a DNA gel 17 What would happen if you ONLY added the four ddNTPs and added NO dNTPs?

18 Copyright © 2012 Pearson Education Inc. Genetics Analysis: An Integrated Approach 18

19 Copyright © 2012 Pearson Education Inc. Genetics Analysis: An Integrated Approach 19 Automated: All terminated chains are in one lane, but each chain has a different ddNTP so is one of four “colors”

20 Copyright © 2012 Pearson Education Inc. Genetics Analysis: An Integrated Approach “Next Generation” DNA Sequencing MANY different methods – but all involve a.small amounts of DNA b.PCR amplification c.Sequencing by synthesis; simultaneous sequencing of many targets Cut DNA into pieces and add “linkers” = defined DNA sequences at both ends of each piece. Physically separate each linker-DNA fragment from the next (e.g. bound to beads). Add primer (complement to linker) - PCR amplify to generate many identical molecules on the same bead. Add primer (complement to linker), polymerase and colored dNTPs – “identify” each dNTP as it is added (reversible stop to replication) Computer “reads” the sequence on thousands of beads (thousands of different DNA sequences) simultaneously 20

21 Copyright © 2012 Pearson Education Inc. Genetics Analysis: An Integrated Approach Transcription… DNA into RNA (mRNA or pre-mRNA) Up to now, we have been describing DNA structure and the process of replicating DNA = semi-conservative DNA replication But why make and replicate DNA? It is the genetic material that dictates attributes of the organism = GENES leading to PHENOTYPES 21

22 Copyright © 2012 Pearson Education Inc. Genetics Analysis: An Integrated Approach 1.3 Transcription and Translation Express Genes The central dogma of biology describes the flow of hereditary information; the original was proposed by Francis Crick 22

23 Copyright © 2012 Pearson Education Inc. Genetics Analysis: An Integrated Approach Mechanisms of Gene Expression Shared by Eukarya, Bacteria, and Archaea (model systems for study) In transcription, one DNA strand is used to direct RNA synthesis – to give rise to mRNA Messenger RNA (mRNA) undergoes translation to produce proteins at nucleoprotein structures called ribosomes These processes deciphered in the 1960’s 23

24 Copyright © 2012 Pearson Education Inc. Genetics Analysis: An Integrated Approach Types of RNA Several types of RNA are produced in a cell; messenger RNA (mRNA) is the only type that is translated Ribosomal RNA (rRNA) forms part of the ribosomes Transfer RNA (tRNA) carries amino acids to ribosomes, to be assembled into proteins 24

25 Copyright © 2012 Pearson Education Inc. Genetics Analysis: An Integrated Approach Additional Features of an Updated Central Dogma Reverse transcription uses reverse transcriptase and an RNA template (from RNA-containing viruses) to produce complementary DNA Micro-RNAs are small RNA molecules with roles in regulation of gene expression in plants and animals 25

26 Copyright © 2012 Pearson Education Inc. Genetics Analysis: An Integrated Approach 26 RNA Polymerase makes a complementary copy (the complement) of the Template strand, adding nucleotides to the mRNA from 5’ to 3’ CODING vs TEMPLATE DNA strands DNA and RNA Polymerases BOTH add nucleotides in 5’ to 3’ direction

27 Copyright © 2012 Pearson Education Inc. Genetics Analysis: An Integrated Approach Identification of Messenger RNA In the late 1950s, researchers used the pulse-chase technique to follow the trail of newly synthesized RNA in eukaryotic cells how can you specifically “label” RNA (not DNA)? The pulse exposed cells to radioactive nucleotides followed by a chase of nonradioactive nucleotides The radiolabeled RNA molecules were then traced in the cells 27

28 Copyright © 2012 Pearson Education Inc. Genetics Analysis: An Integrated Approach Experiments in Eukaryotes In eukaryotic cells that were pulsed with radioactive uracil, the radioactivity was initially concentrated in the nucleus Over a short period of time, the radioactivity moved to the cytoplasm This led researchers to conclude that RNA synthesized in the nucleus carried its information to the cytoplasm for translation into protein 28

29 Copyright © 2012 Pearson Education Inc. Genetics Analysis: An Integrated Approach RNA Synthesis RNA polymerase catalyzes the addition of each ribonucleotide to the 3 end of the nascent strand and forms the phosphodiester bonds between nucleotides Two phosphates are eliminated in the process, as in DNA synthesis 29

30 Copyright © 2012 Pearson Education Inc. Genetics Analysis: An Integrated Approach 30 Note: NTPs, not dNTPs…

31 Copyright © 2012 Pearson Education Inc. Genetics Analysis: An Integrated Approach Bacterial Transcription will be covered in a later lecture (lectures 15 and/or 16) 31

32 Copyright © 2012 Pearson Education Inc. Genetics Analysis: An Integrated Approach Eukaryotes: similar 5 core subunits + 6-11 additional subunits

Download ppt "Telomeres The leading strand of linear chromosomes can be replicated to the end The lagging strand addition of sequential RNA primers as polymerase moves."

Similar presentations

Chapter 10 Table of Contents Section 1 Discovery of DNA

Chapter 10 Table of Contents Section 1 Discovery of DNA
Chapter 10 Table of Contents Section 1 Discovery of DNA

Chapter 10 Table of Contents Section 1 Discovery of DNA
DNA, RNA, and Protein Synthesis

DNA, RNA, and Protein Synthesis
Chapter 10 Table of Contents Section 1 Discovery of DNA

Chapter 10 Table of Contents Section 1 Discovery of DNA
Protein Synthesis Genome - the genetic information of an organism DNA – in most organisms carries the genes RNA – in some things, for example retroviruses.

Protein Synthesis Genome - the genetic information of an organism DNA – in most organisms carries the genes RNA – in some things, for example retroviruses.
1 2 3 4 Review: Proteins and their function in the early stages of replication 1 = initiator proteins 2 = single strand binding proteins 3 = helicase 4.

Review: Proteins and their function in the early stages of replication 1 = initiator proteins 2 = single strand binding proteins 3 = helicase 4.
LE 16-7 5 end 3 end 5 end 3 end Space-filling modelPartial chemical structure Hydrogen bond Key features of DNA structure 0.34 nm 3.4 nm 1 nm The mechanism.

LE end 3 end 5 end 3 end Space-filling modelPartial chemical structure Hydrogen bond Key features of DNA structure 0.34 nm 3.4 nm 1 nm The mechanism.
1 Molecular genetics of bacteria Emphasis: ways that bacteria differ from eukaryotes DNA structure and function; definitions. DNA replication Transcription.

1 Molecular genetics of bacteria Emphasis: ways that bacteria differ from eukaryotes DNA structure and function; definitions. DNA replication Transcription.
Biological Information Flow

Biological Information Flow
DNA Structure Replication Functions (Stores and provides copies of genetic material- genes) – Blueprint (genes) for Protein Synthesis (Enzymes and cell.

DNA Structure Replication Functions (Stores and provides copies of genetic material- genes) – Blueprint (genes) for Protein Synthesis (Enzymes and cell.
SC.L.16.3 Describe the basic process of DNA replication and how it relates to the transmission and conservation of the genetic information.

SC.L.16.3 Describe the basic process of DNA replication and how it relates to the transmission and conservation of the genetic information.
DNA Form & Function.

DNA Form & Function.
Relationship between Genotype and Phenotype

Relationship between Genotype and Phenotype
DNA Structure and Replication And a brief introduction to RNA.

DNA Structure and Replication And a brief introduction to RNA.
Unit 4 - Molecular Genetics DNA Replication Protein Synthesis – Transcription – Translation Cell Cycle.

Unit 4 - Molecular Genetics DNA Replication Protein Synthesis – Transcription – Translation Cell Cycle.
Nucleic Acids and DNA Replication. 1. What is the role of nucleic acid? 2. What is the monomer of a nucleic acid? 3. The monomer of a nucleic acid is.

Nucleic Acids and DNA Replication. 1. What is the role of nucleic acid? 2. What is the monomer of a nucleic acid? 3. The monomer of a nucleic acid is.
DNA Chapter 10.

DNA Chapter 10.
Microbial Genetics: DNA and RNA What chemical carries the genetic instructions in cells, and how is this chemical reproduced? How is this chemical used.

Microbial Genetics: DNA and RNA What chemical carries the genetic instructions in cells, and how is this chemical reproduced? How is this chemical used.
Molecular Genetics DNA Structure  Nucleotides  Consist of a five-carbon sugar, a phosphate group, and a nitrogenous base 12.1 DNA: The Genetic Material.

Molecular Genetics DNA Structure  Nucleotides  Consist of a five-carbon sugar, a phosphate group, and a nitrogenous base 12.1 DNA: The Genetic Material.
Unit 9: The Central Dogma Honors Biology.  The process of DNA replication is fundamentally similar for prokaryotes and eukaryotes.  DNA replication.

Unit 9: The Central Dogma Honors Biology.  The process of DNA replication is fundamentally similar for prokaryotes and eukaryotes.  DNA replication.

Similar presentations

Ads by Google