DNA RNA PROTEIN

1
DNA ----?RNA---? PROTEIN

• This is the central dogma of molecular biology.
  It is also known as transcription and translation

2
Transcription

• http//207.207.4.198/pub/flash/26/transmenu_s.swf
• VCAC Molecular Processes Transcription The
  Movie
• Animations

3

• Video which shows the research being done with
  RNA NOVA scienceNOW RNAi PBS

4
Overview of process
5
Compare DNA and RNA go to pages 16 and 17 study
guide

• DNA
• Inside nucleus
• Double strand
• Contains A T C G
• Sugar is deoxiribose
• long

• RNA
• Moves outside of nucleus to cytoplasm
• Single stranded
• Contains A U C G
• Relatively small
• Sugar is ribose

6
What do we need for transcription?

• DNA
• DNA is a long chain of basesIn eukaryotes, the
  genome is divided into
• Genes
• Each gene is divided into several exons,
  separated by non coding sequences.
• Introns (not coding)
• Exons (coding)
• Promoters, and regulation sequences.

7
Introns and Exons
8
It is estimated

• In Humans it is estimated that up to 90 (or
  higher) of our DNA is non coding DNA
• Since this will not be used in translation of DNA
  into a protein it must be removed.

9

• Only one strand of DNA (the template strand) is
  transcribed. (Antisense strand )
• The strand left un copied is the sense strand
• RNA nucleotides are available in the region of
  the chromatin
• (this process only occurs during Interphase)

10
So lets begin / go to page 62 of study guide

• Transcription factors attach to a special
  sequence called a promoter (TATA)
• RNA polymerase II attaches and begins attaching
  RNA nucleotide bases in a 53 direction

11
Look at mRNA and sense strand
12
remember

• In transcription the nucleotides are
• A U G C or in reading this
• DNA C A C G T T C G
• RNA G U G C A A G C
• So C still goes with G
• But DNA A goes with RNA U (uricil replaces
  thymine in RNA. No T should be found in an RNA
  strand.

13
Polymerization

• Once the polymerase is attached to DNA , and
  locked on the DNA by the transcription factors,
  it catalyses the addition of nucleotides from 5'
  to 3'... (a nucleotide is attached to the 3' OH
  of its preceding nucleotide).

14

• Termination signals in the DNA indicate the end
  of the gene to be transcribed.
• It is a signal for the termination of
  transcription and RNA poly II and transcription
  factors are released.
• This long RNA is called pre mRNA, and needs
  further modification before being transported
  into the cytoplasm and translated into protein

15
Modification of pre mRNA

• RNA is stable after a few modification steps.
• This mRNA is going into the cytoplasm where there
  are many enzymes which would be detrimental to
  the messenger.
• Or
• DONT KILL THE MESSENGER!!!!!

16

• Capping most mRNAs have their starting end
  blocked by the addition of a cap to the 5 end
• Addition of a poly-A tail to 3 end
• ( made up of adenines) segment is 100 to 200
  nucleotides long

17
Splicing

• Remember DNA carries introns or non coding area
• These also will be sliced using a splisosome
  complex

18
(No Transcript)
19
The final product

• messenger RNA. It is used as a template for the
  synthesis of protein by ribosomes.
• Processing of Gene Information - Prokaryotes
  versus Eukaryotes

20
(No Transcript)
21
Translation or mRNA to a polypeptide

• In protein synthesis, the translation of RNA into
  a polypeptide, and the involvement of the
  ribosomes are the most important parts of the
  process.
• There are three types of ribosomes. We have the
  messenger already and now in come rRNA and tRNA

22
The 3 types of RNA
23
r RNA or ribosomal RNA page 63 study guide

• Ribosomes are the sites where the cell assembles
  proteins according to genetic instructions
• They consist of two parts and are located either
  free floating in the cytoplasm or bound to the
  endoplasmic reticulum remember that from earlier
  this year?

24
(No Transcript)
25
(No Transcript)
26
(No Transcript)
27
tRNA or transfer RNA page 63 study guide

• Transfer RNA (tRNA) is basically
  cloverleaf-shaped.
• tRNA carries the proper amino acid to the
  ribosome when the codons call for them.
• At the top of the large loop are three bases, the
  anticodon, which is the complement of the codon
• Now what is a codon????

28
Codons page 63 study guide

• The genetic code is written in triplets of bases,
  called CODONS. 64 possible words, but 20 amino
  acids. Turns out that many amino acids are
  designated by multiple triplets.   The code is
  redundant. Still, some left over as special
  signals -- stop codons,marking the end of genes.

29
(No Transcript)
30
Back to tRNA

• tRNAs bring in the amino acids.
• Each is specific for the amino acid it will carry
• There are 20 amino acids and 64 codons. This is a
  redundancy of codes
• The anticodon is complimentary to the codon

31
Process of translation

• http//207.207.4.198/pub/flash/26/transmenu_s.swf
• Animations
• Protein Synthesis Animation
• VCAC Molecular Processes Translation
• Translation

32
(No Transcript)
33
Another look at tRNA
34
overview

• Animations
• Protein Synthesis
• Translation

35
So here it goespage 65 study guide

• In the first step in protein synthesis, the small
  subunit of the ribosome binds to the mRNA
  molecule at the start codon
• Initiation
• The first tRNA delivers its amino acid
• The larger unit or rRNA is also attached

36
(No Transcript)
37
Elongation

• Begins when the next tRNA binds to the A site of
  the ribosome
• The first tRNA is released after the amino acid
  is taken
• The next  tRNA moves from the A site to the P
  site
• and the used tRNA moves to the E site where it is
  released
• This process continues until it reaches the stop
  codon.

38
(No Transcript)
39
Termination

• The ribosome reaches the stop codon.
•   The polypeptide is released along with the two
  ribosomal units

40
Not done yet.

• What has been made is a polypeptide chain
• This must be now further processed into a protein
• Remember how the ribosomes may be attached to the
  Endoplasmic Reticulum
• So the polypeptide chain (if for export) is going
  to through the ER to the Golgi and out of the
  cell (exocytosis)

41

• The unattached ribosomes or free floating
  ribosomes will process those polypeptides for use
  in the cell
• Sometimes multiple copies of the mRNA are read
  and processed . These are called polysomes

42
Electron Micrograph of a Polysome Chain

43
And so..

• DNA is copied into mRNA inside the nucleus.
• The mRNA moves into the cytoplasm and tRNA and
  rRNA join up to read the message and produce a
  polypeptide chain
• This will be further processed into a protein

44

• Prokaryotes regulate gene expression by
  controlling transcription, in one of two ways
  either the presence of the substrate induces the
  transcription of the gene specifying an enzyme
  that acts on that substrate, or the presence of
  the product of an enzyme represses transcription
  of the gene specifying that enzyme.

45

• The lac operon is an inducible system, meaning
  that the presence of the substrate lactose
  induces transcription of the genes specifying the
  enzymes necessary for its digestion. When lactose
  is absent, the repressor protein binds to the
  operator and prevents transcription. When lactose
  is present, it binds to the repressor protein,
  changing its shape in a way that prevents it from
  binding to the operator, and so transcription is
  permitted.

46
lac operon an inducible operon because it is
always OFF, but it can be turned ON.
47
(No Transcript)
48

• the trp operon a repressible operon
• it is always ON, but it can be turned OFF.

49
How it works

• When lactose is present
• The repressor is inactive
• The repressor falls off the operator
• RNA polymerase binds to the promoter
• Z,Y, and a genes are transcribed

• When lactose is absentThe repressor is
  activeThe repressor binds to the operatorRNA
  polymerase cannot bind to the promoterZ,Y, and a
  are not transcribed

50
Control- operons

• The lac Operon
• http//trc.ucdavis.edu/biosci10v/bis10v/week6/lac_
  negative.mov

51

• the trp operon a repressible operon
• it is always ON, but it can be turned OFF.

52

• The cell needs tryptophan, so it makes it. 
  But... what happens if the cell suddenly finds
  itself in an environment where tryptophan is
  available?  The cell would MUCH rather just take
  that tryptophan up from the environment, rather
  than continue the energy-intensive process of
  manufacturing its own!  Therefore, it must have a
  way to shut OFF the trp operon.

53

• Tutorial 13.2 The trp Operon
• BIOL 230 Lecture Guide - Animation of the trp
  Operon in the Absence of a Corepressor

54
control

• eLearning ( this will go through everything we
  know and need to know. Go to all of the links
  for a great review. )
• Animation Quizzes lac and tryp
• The lac Operon in E. coli Introduction
• PHSchool - The Biology Place

55
Mutations pag 23 sg

• In the living cell, DNA undergoes frequent
  chemical change, especially when it is being
  replicated (in S phase of the eukaryotic cell
  cycle). Most of these changes are quickly
  repaired. Those that are not result in a
  mutation. Thus, mutation is a failure of DNA
  repair.

56
Single-base substitutions

• A single base, say an A, becomes replaced by
  another. Single base substitutions are also
  called point mutations.
• Sickle cell anemia is a point mutation
• Teachers' Domain A Mutation Story

57

• Missense mutations (point mutation)-With a
  missense mutation, the new nucleotide alters the
  codon so as to produce an altered amino acid in
  the protein product

58
Sickle cell anemia

• The replacement of A by T at the 17th nucleotide
  of the gene for the beta chain of hemoglobin
  changes the codon GAG (for glutamic acid) to GTG
  (which encodes valine).

59
Nonsense mutations(point mutation)

• With a nonsense mutation, the new nucleotide
  changes a codon that specified an amino acid to
  one of the STOP codons (TAA, TAG, or TGA).
  Therefore, translation of the messenger RNA
  transcribed from this mutant gene will stop
  prematurely. The earlier in the gene that this
  occurs, the more truncated the protein product
  and the more likely that it will be unable to
  function.

60
Cystic fibrosis is an example

• cystic fibrosis the substitution of a T for a C
  at nucleotide 1609 converted a glutamine codon
  (CAG) to a STOP codon (TAG). The protein produced
  by this patient had only the first 493 amino
  acids of the normal chain of 1480 and could not
  function.

61
Silent mutations

• Most amino acids are encoded by several different
  codons. For example, if the third base in the TCT
  codon for serine is changed to any one of the
  other three bases, serine will still be encoded.
  Such mutations are said to be silent because they
  cause no change in their product and cannot be
  detected without sequencing the gene (or its
  mRNA).

62

• Cracking the code from PBS ( who else)
• NOVA Online Cracking the Code of Life Watch
  the Program Here
• Watch 1,3,6,9,10.12.14.

63
Beadle and Tatum (1940's) One Gene, One Enzyme
(pg 18 sg)

• Using genetic and biochemical approaches with
  bread mold (Neurospora crassa), Beadle and Tatum
  devised the first hypothesis about the functional
  nature of genes.
• Hypothesis Genes specify proteins. A defective
  protein leads to an inherited disorder DNA
  Interactive

64
(No Transcript)
65
(No Transcript)
66
Beadle Tatum one gene one enzyme

• One gene makes one protein. ltscript
  src"http//www.google-analytics.com/urchin.js"
  type"text/javascript"gtlt/scriptgt ltscript
  type"text/javascript"gt _uacct "UA-66701-2"
  urchinTracker() lt/scriptgt