Chapter 13: RNA & Protein Synthesis 12-3 RNA and Protein Synthesis Section: 13–1 RNA

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12–3 RNA and Protein Synthesis

12–3 RNA and Protein Synthesis

Genes contain coded DNA instructions that tell cells how to build of proteins.

Genetic instructions can be decoded by copying part of the nucleotide sequence from DNA into RNA.

RNA then uses the genetic instructions or coded information for making proteins. Slide 2 of 39 Copyright Pearson Prentice Hall

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12–3 RNA and Protein Synthesis

The Structure of RNA

The Structure of RNA There are three main differences between RNA and DNA:

•The sugar in RNA is ribose instead of deoxyribose. •RNA is generally single-stranded. •RNA contains uracil in place of thymine.

• When RNA identifies adenine it substitutes uracil in place of thymine

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12–3 RNA and Protein Synthesis

Types of RNA

Types of RNA There are three main types of RNA:

• messenger RNA • ribosomal RNA • transfer RNA

(mRNA) (rRNA) (tRNA)

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12–3 RNA and Protein Synthesis

Types of RNA

Messenger RNA (mRNA) carries copies of instructions for assembling amino acids into proteins. Slide 5 of 39 Copyright Pearson Prentice Hall

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12–3 RNA and Protein Synthesis

Types of RNA

Ribosome

Ribosomal RNA

Ribosomes are made up of proteins and ribosomal RNA (rRNA). Proteins are assembled on ribosomes. Slide 6 of 39 Copyright Pearson Prentice Hall

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12–3 RNA and Protein Synthesis

Types of RNA

Amino acid

Transfer RNA

During protein construction, transfer RNA (tRNA) transfers each amino acid to the ribosome. Slide 7 of 39 Copyright Pearson Prentice Hall

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12–3 RNA and Protein Synthesis

Transcription

RNA RNA polymerase DNA

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12–3 RNA and Protein Synthesis

Transcription

Transcription DNA is copied in the form of RNA This first process is called transcription. The process begins at a section of DNA called a promoter. Promoters show RNA polymerase exactly where to begin making RNA. Slide 9 of 39 Copyright Pearson Prentice Hall

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12–3 RNA and Protein Synthesis

Protein Synthesis

DNA molecule

DNA strand (template)

5′

3′

TRANSCRIPTION

mRNA

5′

3′ Codon

TRANSLATION

Protein

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12–3 RNA and Protein Synthesis

RNA Editing

RNA Editing Some DNA within a gene is not needed to produce a protein. These areas are called introns. The DNA sequences that code for proteins are called exons.

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12–3 RNA and Protein Synthesis

The introns are cut out of RNA molecules.

Exon Intron

The exons are then spliced together to form mRNA. Then a cap and tail are added to to form the final mRNA molecule.

RNA Editing

DNA

Pre-mRNA

mRNA

Cap

Tail Slide 12 of 39

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Chapter 13: RNA and Protein Synthesis 12-3 RNA and Protein Synthesis Section: 13–2 Ribosomes and Protein Synthesis

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12–3 RNA and Protein Synthesis

The Genetic Code

The Genetic Code The genetic code is the “language” of mRNA instructions. The code is written using four “letters” (the bases: A, U, C, and G).

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12–3 RNA and Protein Synthesis

The Genetic Code

Genetic codes are read 3 bases at a time. A codon consists of three consecutive nucleotides on mRNA that specify a particular amino acid. There are about 20 different amino acids.

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12–3 RNA and Protein Synthesis

The Genetic Code

There are 64 possible 3-base codes.

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Start codon Copyright Pearson Prentice Hall

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12–3 RNA and Protein Synthesis

Translation

Translation

Translation is the decoding of an mRNA message into a a series of amino acids which form the polypeptide chain (protein). Translation takes place on ribosomes in the cytoplasm. During translation, the cell uses information from messenger RNA to produce proteins. Nucleus

mRNA Copyright Pearson Prentice Hall

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12–3 RNA and Protein Synthesis

Translation

The ribosome binds new tRNA molecules and amino acids as it moves along the mRNA. Phenylalanine

tRNA

Lysine

Methionine tRNA Anti-codon

Ribosome

mRNA

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12–3 RNA and Protein Synthesis

Translation

Protein Synthesis Lysine

tRNA

Translation direction

mRNA Ribosome

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12–3 RNA and Protein Synthesis

Translation

The process continues until the ribosome reaches a stop codon. Polypeptide Ribosome tRNA

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mRNA Copyright Pearson Prentice Hall

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12–3 RNA and Protein Synthesis Codon

Genes and Proteins Codon Codon

DNA Single strand of DNA Codon Codon Codon

mRNA mRNA

Protein

Alanine Arginine Leucine

Amino acids within a polypeptide Copyright Pearson Prentice Hall

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12–3

The role of a master plan in a building is similar to the role of which molecule? a. messenger RNA b. DNA c. transfer RNA d. ribosomal RNA

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12–3

A base that is present in RNA but NOT in DNA is a. thymine. b. uracil. c. cytosine. d. adenine.

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12–3

The nucleic acid responsible for bringing individual amino acids to the ribosome is a. transfer RNA. b. DNA. c. messenger RNA. d. ribosomal RNA.

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A region of a DNA molecule that indicates to an enzyme where to bind to make RNA is the a. intron. b. exon. c. promoter. d. codon.

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A codon typically carries sufficient information to specify a(an) a. single base pair in RNA. b. single amino acid. c. entire protein. d. single base pair in DNA.

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Chapter 13: RNA & Protein Synthesis Section: 13–3 Mutations 12-4 Mutations

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12–4 Mutations

12-4 Mutations

Mutations are changes in the genetic material.

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12–4 Mutations

Kinds of Mutations

Kinds of Mutations Mutations that produce changes in a gene are known as gene mutations. Mutations that produce changes in whole chromosomes are known as chromosomal mutations.

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12–4 Mutations

Kinds of Mutations

Gene Mutations Gene mutations involving a change in one or a few nucleotides are known as point mutations because they occur at a single point in the DNA sequence. Point mutations include: substitutions, insertions, and deletions. Point mutations usually occur during replication. Sickle-cell disease is the result of a point mutation. Slide 32 of 24 Copyright Pearson Prentice Hall

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12–4 Mutations

Kinds of Mutations

Substitutions usually affect no more than a single amino acid. One base is changed to another base (e.g., T and A are substituted for C and G) Slide 33 of 24 Copyright Pearson Prentice Hall

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12–4 Mutations

Kinds of Mutations

The effects of insertions or deletions (types of point mutations) are more dramatic.

The addition or deletion of a nucleotide causes a shift in the grouping of codons that are read.

Changes like these are called frameshift mutations.

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12–4 Mutations

Kinds of Mutations

In an insertion, an extra base is inserted into a base sequence. Note the changes in amino acids before the insertion (top) and after the insertion (bottom). This protein produced will not be able to perform its normal function. Slide 35 of 24 Copyright Pearson Prentice Hall

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12–4 Mutations

Kinds of Mutations

In a deletion, the loss of a single base is deleted and the reading frame is shifted.

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12–4 Mutations

Kinds of Mutations

Chromosomal Mutations Chromosomal mutations involve changes in the number or structure of chromosomes. There are 4 types of chromosomal mutations include:

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deletions, duplications, inversions, and translocations. Slide 37 of 24 Copyright Pearson Prentice Hall

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12–4 Mutations

Kinds of Mutations

Deletions involve the loss of all or part of a chromosome.

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12–4 Mutations

Kinds of Mutations

Duplications produce extra copies of parts of a chromosome.

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12–4 Mutations

Kinds of Mutations

Inversions reverse the direction of parts of chromosomes.

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12–4 Mutations

Kinds of Mutations

Translocations occurs when part of one chromosome breaks off and attaches to another.

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12–4 Mutations

Significance of Mutations

Significance of Mutations Many mutations have little or no effect on gene expression. Some mutations can be beneficial (e.g., oil eating bacteria). It is estimated that there is 1 incorrect base insertion for every 10,000,000 bases. Slide 42 of 24 Copyright Pearson Prentice Hall

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12–4 Mutations

Significance of Mutations

Significance of Mutations Some mutations are the cause of environmental conditions. Mutagens can cause genetic disorders. Chemical mutagens: pesticides, tobacco smoke are some. Physical mutagens: x-rays, UV light are some examples

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12–4 Mutations

Significance of Mutations

Significance of Mutations Mutations in some African mosquitoes have caused them to be resistant to pesticides. Polyploidy (triploids 3n and tetraploids 4n), is the condition in which an organism has extra sets of chromosomes. Examples: apples, limes, (most citrus), strawberries, mums, dahlias, pansies, some wheat, bananas, oats, kiwi, sugar cane, watermelon, tulips, lilies, cotton, tobacco, peanuts… Slide 44 of 24 Copyright Pearson Prentice Hall

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A mutation in which all or part of a chromosome is lost is called a(an) a. duplication. b. deletion. c. inversion. d. point mutation.

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A mutation that affects every amino acid following an insertion or deletion is called a(an) a. frameshift mutation. b. point mutation. c. chromosomal mutation. d. inversion.

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