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Chapter 12-3: RNA and Protein Synthesis

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Chapter 12-3: RNA and Protein Synthesis Frameshift mutations (Insertions or Deletions): an extra base is added or removed. These usually affect a large part of the ... – PowerPoint PPT presentation

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Title: Chapter 12-3: RNA and Protein Synthesis


1
Chapter 12-3 RNA and Protein Synthesis
2
What is a gene?
  • A gene is a set of DNA instructions that control
    the synthesis of proteins within the cell.
  • This process, called protein synthesis, involves
    2 steps transcription and translation.

3
How does a gene work?
  • DNA cannot leave the nucleus, so a copy is made
    in the form of a similar nucleic acid called RNA
    (ribonucleic acid) during transcription. After
    DNA is used to make RNA, the RNA is then used to
    make proteins during translation by ribosomes in
    the cytoplasm.

4
How is DNA different from RNA?
  • RNA is a nucleic acid similar to DNA with 3
    differences
  • RNA contains the sugar ribose and DNA contains
    the sugar deoxyribose
  • RNA is single-stranded, DNA is double-stranded

5
How is DNA different from RNA?
  1. RNA contains uracil instead of thymine. Uracil,
    like thymine, is a pyrimidine (contains one
    ring).

6
Three types of RNA
  • messenger RNA (mRNA)
  • carries a copy of the information in DNA.
  • This type of RNA acts as a messenger bringing
    the information in the DNA to the ribosome.

7
  • ribosomal RNA (rRNA)
  • this RNA is found with ribosomes.
  • Recall that ribosomes synthesize proteins.
  • Ribosomes are made of both proteins and rRNA.

2 subunits
8
Label this figure on your notes! Transfer RNA
  • 3. transfer RNA (tRNA)
  • this RNA brings amino acids to the ribosome to
    be added to the polypeptide chain that is being
    made at the ribosome.
  • There is one tRNA for each of the 20 amino acids.

Amino acid
tRNA
anticodon
9
Central Dogma of Molecular Biology
  • See board

10
Transcription
  1. Transcription is the process in which the
    nucleotide sequence of DNA is copied, or
    transcribed into a complementary nucleotide
    sequence of RNA.
  2. DNA is like the master plan and RNA is like the
    blueprint. The master plan stays in the
    nucleus (the office) and the blueprint can be
    taken to the ribosome (construction site).
  3. Because DNA is in the nucleus, transcription
    occurs in the nucleus of the cell.
  4. When transcription is finished, the RNA moves to
    the cytoplasm. DNA cannot leave the nucleus!!

11
Transcription
  • 5. The enzyme RNA polymerase is used to make
    RNA. RNA polymerase
  • A. binds to the DNA,
  • B. separates the DNA, and
  • C. uses only one strand of DNA as a template to
    make a complementary RNA strand. RNA Polymerase
    reads 3 ? 5

12
Transcription
D. Once RNA is made, the RNA detaches from the
template strand, leaves the nucleus through
nuclear pores, and enters the cytoplasm of the
cell
RNA polymerase
DNA
RNA
How does RNA look different than DNA? Do RNA and
DNA leave the nucleus?
13
Video Clip Transcription
14
Translation
  1. RNA is used to make protein in a process called
    translation.
  2. Remember that proteins, a.k.a. polypeptides, are
    macromolecules made of monomers called amino
    acids.

15
  • The Genetic Code
  • In RNA, the nucleotides are read in words made
    of 3 nucleotide letters. Each word is called
    a codon and contains the genetic code for one
    amino acid.

Move from the inside out!
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  • The first word or start codon is always the
    same for every protein. It is always AUG. Using
    the genetic code wheel you can figure out which
    amino acid a codon represents. What amino acid
    is associated with the codon AUG?
  • There are a total of 20 different amino acids
    that can be arranged in different ways to make
    different proteins.

Methionine
18
Activity 1
Transcription in nucleus
Translation in cytoplasm
19
Translation
  1. During translation, ribosomes decode the mRNA
    message (made of nucleotides) to make polypeptide
    chains (made of amino acids). Ribosomes read 5
    ? 3 on the mRNA.
  2. Before translation can occur, mRNA must be made
    from DNA in transcription. Transcription occurs
    in the nucleus, then the mRNA travels out of the
    nucleus into the cytoplasm.
  3. Translation is done by ribosomes in the
    cytoplasm.

20
  • The steps in translation include
  • 1. Two subunits of the ribosome attach to the
    mRNA.

21
  1. Ribosomes read 5 ? 3. As each codon of the
    mRNA moves through the ribosome, the correct
    amino acid is brought to the ribosome by tRNA.
  2. Each tRNA molecule has a group of three
    nucleotides called the anticodon. These three
    nucleotides pair with the nucleotides in the
    codon. The tRNA molecule also has an amino acid
    attached.

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  • 4. Peptide bonds form between amino acids to
    form the polypeptide chain in a process called
    elongation because it makes the polypeptide chain
    longer.

24
  • This forms a peptide bond between the amino
    acids. This is why proteins are called
    polypeptides.
  • The empty tRNA molecule exits the mRNA and is
    recycled by the cell and can bind another amino
    acid.

25
  1. The ribosome continues to match the codons in the
    mRNA with anticodons in tRNA until it reads a
    codon in the mRNA that says stop. A tRNA for
    stop does not carry an amino acid. No peptide
    bond will form, so the ribosome releases the mRNA
    and the protein.

6. Polypeptide will start to coil and bend,
forming the 3-D shape of proteins (recall the 4
level of protein structure)
26
Video Clip Translation
27
Why are proteins important?
  • Each protein has a specific function within
    living cells. Some functions of proteins are
  • acting as enzymes, to speed up and regulate
    chemical reactions.
  • making pigments that determine flower color in
    plants
  • determining your blood type.
  • regulating cell growth and development.

28
Where in the cell does transcription
occur? -Nucleus
Where in the cell does translation occur?
-Cytoplasm
29
Chapter 12-4 Mutations
30
  • Mutations are changes in the genetic code. They
    come from mistakes that cells have made in
    copying their own DNA. If a cell has a mutation,
    all of its daughter cells will have that same
    mutation.

31
  • Kinds of mutations
  • Mutations come in many shapes and sizes.
  • Mutations that produce a change in a single gene
    are called gene mutations.
  • Other mutations produce changes in whole
    chromosomes (and affect many genes). These
    mutations are called chromosomal mutations.

32
Gene mutations affect one gene
  • Point mutations involve changes in one or a few
    nucleotides at one point in the DNA sequence.
  • Substitutions where one base is changed to
    another. These usually affect only one amino
    acid.

33
Original DNA The fat cat ate the rat. Mutant
DNA The fat hat ate the rat. (substitution)
Substitution
34
  • Frameshift mutations (Insertions or Deletions)
    an extra base is added or removed. These
    usually affect a large part of the protein.
    Remember, bases are read in groups of three, but
    if one base is added or removed, this shifts the
    reading frame of the genetic code and can
    change all amino acids after the site of the
    mutation

Original DNA The fat cat ate the rat. Mutant
DNA The fat cat tat eth era t. (insertion)
Insertion
35
  • Frameshift mutations (Insertions or Deletions)
    an extra base is added or removed. These
    usually affect a large part of the protein.
    Remember, bases are read in groups of three, but
    if one base is added or removed, this shifts the
    reading frame of the genetic code and can
    change all amino acids after the site of the
    mutation

Deletion
TAG CAT GGA AT
AUC GUA CCU UT
Val
Pro
Ile

36
Video Clip Point Mutations
37
  1. Chromosomal mutations involve changes in the
    number or structure of the chromosomes.
  • Can change the locations of genes on chromosomes
  • Inversion reverses the direction of parts of
    the chromosomes
  • Translocation part of one chromosome breaks off
    and attaches to another.

38
Video Clip Translocation and Inversion
39
  • Can change the number of copies of some genes
  • Deletion a part of the chromosome is lost
  • Duplication there is an extra copy of part of
    the chromosome

40
Video Clip Duplication and Deletions
41
  Effects of Mutations
  1. Neutral No effect on protein function
  2. Harmful Cause genetic diseases
  3. Beneficial Plants with extra sets of
    chromosomes are larger and stronger
  4. Any new trait in a population, good or bad, is a
    result of a mutation.

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