Biology Chapter 13 RNA and Protein Synthesis - PowerPoint Presentation

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Biology Chapter 13

RNA and Protein Synthesis

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I. RNA [13.1]

A. Describe RNA –

Ribonucleic AcidB. Differences between DNA and RNA

DNARNA

DeoxyriboseRibose

Double-strandedSingle-stranded

G, C, A, Thymine

G, C, A, Uracil

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C. Types of RNA

1. mRNA - (messenger RNA) carries protein synthesis instructions from nucleus to ribosomes 2. tRNA -

(transfer RNA) carries amino acids toribosomes, matches A. A. to mRNA 3. rRNA - (ribosomal RNA) forms portion of ribosomes (rest is protein)

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II. Gene Expression (starting with RNA synthesis) [13.1]

A. TRANSCRIPTION (just a short description)-

Changing DNA codes into RNA codes B. GENE –

Portion of DNA which codes for a particular protein C. Enzyme involved – RNA Polymerase D. PROMOTOR REGION – Region of DNA which is recognized by RNA polymerase (often multiple TACTACTAC triplets)

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E. Sequence (of RNA Transcription)

1. Unwind section of DNA 2. “Sense” strand of DNA is rewritten into a complementary

strand of mRNA 3. Transcription proceeds from promoter region toward termination sequence 4. In Eukaryotes, mRNA moves out of the nucleus to ribosomes

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5. In Eukaryotes… there may be RNA editing (pieces removed)

a. INTRONS – discarded portions of mRNA

b. EXONS – remaining pieces of mRNA which are expressedhttp://www.stolaf.edu/people/giannini/flashanimat/molgenetics/transcription.swf

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III. Reading the Genetic Code [13.2]

A. GENETIC CODE – Sequence of nitrogenous bases  B. There are 20 common amino acids; what led to the concept of the triplet code?

1. DNA has four nitrogenous bases: A, G, T, C  a. If the match was 1 base: 1 amino acid, there would be __4___ possible amino acids  b. If the match was 2 bases: 1 amino acid, there would be __16___ possible amino acids  c. If the match was 3 bases: 1 amino acid, there would be __64___ possible amino acids

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2

. With that many possibilities, what happens to all the extra triplets? There are duplications and 3 stop codons

C. CODON – 3-letter sequence of bases in mRNA 1. Start Codon – AUG (methionine) 2. Stop Codons – UGA, UAA, UAG

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IV. Translation

A. TRANSLATION – Converting an mRNA sequence into an amino acid sequence 

B. tRNA is the amino acid carrier. 1. ANTICODON: 3-base sequence on the end of a tRNA molecule It is complementary to a codon!

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C

. Translation Sequence: (at the ribosomes) 1. 6-base section of mRNA is held in place; 2 tRNA molecules match to codons;

dehydration synthesis forms bonds between amino acids 2. after peptide bond forms, 1st tRNA is released ribosome moves 3 bases 3. another tRNA/amino acid moves into place new peptide bond forms process repeats until “stop” codon is reachedhttp://vcell.ndsu.edu/animations/translation/movie.htm

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D

. Central Dogma of Molecular Biology – Information is transferred from DNA to RNA to protein 

  E. GENE EXPRESSION – Process by which DNA, RNA, and proteins are involved in putting a gene to work

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V. Mutations [13.3]

A. GENE MUTATIONS – Inheritable changes at the level of nucleotides (changes in base sequence) 

1. POINT MUTATIONS –  Changes in one or a few nucleotides 2. SUBSTITUTIONS –  One base is exchanged for another a. How will a base substitution affect the protein for which the affected gene codes?1 amino acid is affected (or not –depending on change)

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b

. Example i. The genetic cause of sickle-cell anemia is 

a single nucleotide substitution (1 base in over 1000)  ii. The effect of sickle-cell anemia is hemoglobin molecules form fibers – change the shape of red blood cellshttp://www.rcsb.org/pdb/explore/jmol.do?structureId=4HHB&opt=3&bionumber=1

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3

. FRAMESHIFT MUTATION – Mutations which cause reading frame (3 letters or triplet) to move forward or backward 

a. INSERTION – Adding a base, shifts reading frame 1 base to the right  i. How will an INSERTION affect the protein for which the affected gene codes?All amino acids downstream will be affected and changed

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b

. DELETION –  Removal of a base from a sequence i

. How will a DELETION affect the protein for which the affected gene codes? All the amino acids downstream from the mutation will changeTHE CAT ATE THE RATTHE ICA TAT ETH ERA T INSERTION THE ATA TET HER AT

DELETION

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c. MISSENSE MUTATION

–

Single base change which alters one amino acid in a chain

as opposed to frameshift that alters all the downstream amino acidsd. NONSENSE MUTATION - Single base change which causes a stop codon to be transcribed, bringing transcription to an early halt

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e. SILENT MUTATION -

Single base change which alters a triplet, but translation produces the same amino acid (due to duplicate triplet codes)

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B. CHROMOSOMAL MUTATION –

change in structure of a chromosome 1. Quickly describe the effects of the following mutations:

a. DELETION – removal (loss) of a section or a whole chromosome b. DUPLICATION – extra copy of a section or a whole chromosome example: Trisomy 21, Trisomy 13

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c. INVERSION –

reversal of direction of a section of chromosome d. TRANSLOCATION –

part of one chromosome gets moved from one to another

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C

. Causes of Mutations and Cancer– 1. MUTAGEN – agent which can cause a mutation

a. Examples – UV light, Pesticides, X-rays, 2. CARCINOGEN mutagen which can specifically cause cancer

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D. How can mutations be harmful to organisms?

Cell Death Cancer

E. How can mutations be helpful to organisms? New genetic combinations – may improve on previous condition

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VI. Gene Regulation [13.4]

A. A Prokaryotic Example – The Lac Operon B. Vocabulary 1. OPERON –

Group of genes that are regulated together  2. OPERATOR – Portion of DNA which can prevent access to structural genes

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3

. REPRESSOR –

 Molecule which binds to operator – prevents transcription  4. INDUCER –

Molecule which changes shape of repressor; this allows RNA polymerase access to structural genes C. The lac operon produces – Galactosidase

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D. Sequence of events

1.

In order to produce beta

galactosidase, RNA polymerase must (first) bind to – promoter region 2

. In the “off” mode, a ___repressor___ __protein____ is bound to the ___operator__ ____region

__ of the lac operon.

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D. Sequence of events

3. When the operon turns “on”, lactose binds to the __repressor__.

4. The _shape__ _of_ _the_ _repressor_ is changed and it can no longer bind to the ____operator_____.

5. Without the repressor in place – transcription can take placehttp://highered.mcgraw-hill.com/olc/dl/120080/bio27.swfhttp://bcs.whfreeman.com/thelifewire/content/chp13/1302001.html

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E. Repressing the production of an enzyme has an advantage for the organism –

no energy is spent for an enzyme which is unneeded

(lactose is the substrate and the inducer in this system) F. Gene regulation in eukaryotes is much more complicated.

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Additional notes (due to my mistakes)

Mutation Vocabulary

Missense – Single base change which alters one amino acid in a chain As opposed to frameshift that alters all the downstream amino acidsNonsense – Single base change which causes a stop codon to be transcribed, bringing transcription to an early halt

Silent mutation – Single base change which alters a triplet, but translation produces the same amino acid (due to duplicate triplet codes)

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