• DNA and RNA Notes
Part 2
–Protein Synthesis
Genes and Proteins
•
Proteins form and become key cell
structures and regulators of cell
functions
•
Sequence of amino acid makes
specific proteins
•
The sequence of nucleotides in
each gene contains information for
assembling amino acids.
•
It is estimated that each human cell
contains about 80,000 genes
RNA
•RNA – ribonucleic acid
•4 Differences Between DNA and RNA
RNA
DNA
Single Stranded
Double Stranded
Sugar is Ribose
Sugar is Deoxyribose
Adenine, Guanine,
Cytosine, Uracil
RNA can leave the nucleus
Adenine, Guanine,
Cytosine, Thymine
DNA can not leave
nucleus
Instead of thymine, RNA uses uracil.
Notice that RNA is single-stranded
instead of double-stranded.
-ose represents sugars and DNA
and RNA both have different sugars.
DNA – A C G T G A A G C T G T A C A G T C A G G C T A
RNA – U G C A ……now do the rest your self
remember Thymine is replaced with uracil in RNA!
•
•
What is the role of RNA in the cell:
•
DNA provides workers with the instructions for
making the proteins
•
RNA takes the DNA instructions on how a protein is
made then amino acid by amino acid they assemble
the protein.
3 Types of RNA that help to build proteins
•
Messenger RNA (mRNA) – brings information from
the DNA in the nucleus to the ribosome
•
Ribosomal RNA (rRNA) – what ribosomes are made
of and they clamp onto the mRNA and use its
information to assemble amino acids
•
Transfer RNA (tRNA) – transports amino acids to
the ribosome to be assembled into a protein.
Transcription
•
Transcription – enzymes make an RNA copy of a
portion of a DNA strand
•
The process of transcription is similar to replication
except
•
Transcription results in single strand of RNA
•
Does not transcribe the entire strand of DNA
•
Steps of Transcription From DNA to RNA
1. The process of transcription begins as enzymes,
RNA polymerase, unzips the molecule of DNA
2. As the DNA molecule unzips, RNA polymerase
assembles RNA nucleotides using one strand of
the DNA as a template.
3. Only the 3’  5’ template strand of DNA is
transcribed. The RNA complimentary strand
grows in the 5’  3’ direction.
4. Transcription continues until RNA polymerase
reaches a special sequence of nucleotides.
5. mRNA molecule breaks away and mRNA leaves
the nucleus and enters the cytoplasm.
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animation.
animation
Slide 10
The Genetic Code
•
Proteins are built from amino acids
•
20 different amino acids
•
Codon – each set of 3 nitrogen bases represents an
amino acid, which is also called a triplet code
•
The order of nitrogen bases in DNA can determine the
type and order of amino acids in a protein
•
64 different combinations
•
61 code for amino acids
•
3 signal to stop protein synthesis
•
More than 1 codon can code for the same amino
acid
•
Codons represent the same amino acids in all
organisms
•
Gives evidence of evolution
•
Start codon is AUG (methionine)
•
Stop codons are UAA, UAG, UGA
Fig. 14.11, p. 230
Slide 13
Translation From mRNA to Protein
•
Translation – the process of converting the
information in a sequence of nitrogen bases in
mRNA into a sequence of amino acids
•
Takes place at the ribosomes in the cytoplasm
The Role of Transfer RNA
•
To bring the amino acids to the ribosome
•
Correct translation of the mRNA message depends
upon the joining of each mRNA codon with the correct
tRNA molecule
•
tRNA recognizes the mRNA codon, because tRNA has
a sequence of three nucleotides that are complement
of the nucleotides in the codon
•
Anti-Codon – tRNA nucleotides
•
Ex: mRNA – A-C-A
tRNA – U-G-U
DNA –
T–A–C–A–G –G –T–C–G –T–T–A–C–G–G–A–C–T
mRNA –
tRNA –
Amino Acids
anticodon
codon in mRNA
anticodon
amino acid
attachment site
tRNA MOLECULE
amino
acid
OH
amino acid attachment site
Fig. 14.12, p. 231
Slide 14
Translating the mRNA Code
Steps of Translation
1. The first codon of the mRNA strand attaches to a
ribosome
2. tRNA molecules, each carrying a specific amino acid
approach the ribosome
3. tRNA anticodon pairs with mRNA codon
4. The first codon on mRNA is AUG which codes for
amino acid methionine. AUG is the start codon for
protein synthesis
5. A new tRNA molecule carrying an amino acid will pair
with the mRNA codon
6. As the process continues a chain of amino acids is
formed until the ribosome reaches a stop codon on the
mRNA strand UAA, UAG, UGA
Fig. 14.14b, p. 233
Slide 17
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animation.
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Slide 18
12-4 Mutations
Mutation: A Change in DNA
•
Mutation – any change in the DNA sequence that also
changes the protein it codes for
•
Mutations in Reproductive Cells
•
If mutation occurs in egg or sperm the altered
gene would become part of the genetic makeup of
the offspring
•
Sometimes the mutation is so severe that the
embryo does not survive
•
In rare cases a gene mutation may have positive
effects
•
Mutations in Body Cells
•
If the cells DNA is changed this mutation
would not be passed on to offspring
•
But the mutations can cause harm to the
individual
2 Types of Mutations in DNA
1. Point Mutation
•
Is a change in a single base pair in DNA
•
A change in a single letter changes the meaning
of this sentence
2. Frameshift Mutation
•
A mutation in which a single base is added or
deleted from DNA
•
This mutation would cause nearly every amino
acid in the protein after the deletion to be
changed.
Chromosomal Mutations
•
Chromosomal Mutations – changes in chromosomes
during replication. Parts can be broken or lost.
•
They occur in all living organisms, but they are
especially common in plants
•
Although rare, changes in an organisms
chromosome structure do occur.
•
Chromosomal mutations are rarely passed on to the
next generation because:
•
The zygote usually dies
•
The mature organism is usually sterile
•
4 Types of Chromosomal Mutations
1. Deletion – a fragment of a chromosome breaks
off, it can be lost when a cell divides
2. Duplication – the chromosome fragment attaches
to its homologous chromosome, which will then
carry two copies of a certain set of genes
3. Inversion – fragment reattaches to the original
chromosome in the reverse orientation
4. Translocation – a fragment may join a
nonhomologous chromosome
Causes of Mutations
•
Spontaneous Mutations – a mistake in base pairing
during DNA replication. It occurs at random or at any
given moment
•
Mutagen – any agent that can cause a change in DNA
•
Ex. Chemicals, radiation, high temperatures
Repairing DNA
•
When mistakes do occur repair mechanisms fix
mutations
•
Proofreading Enzymes – reads the DNA strand and
checks it for mistakes
•
Repair Enzymes – fixes any mistakes in the DNA
strand
Mistakes in Meiosis
•
Sometimes accidents occur during meiosis and
chromosomes fail to separate correctly
•
Nondisjunction – failure of homologous
chromosomes to separate
•
During meiosis I one chromosome from each pair is
supposed to move to opposite poles but
occasionally both chromosomes of a pair move to
the same pole
•
Trisomy – 1 extra chromosome (47)
•
•
Ex: extra chromosome on pair number 21 – down
syndrome
Monosomy – missing 1 chromosome (45)
•
Ex: missing chromosome on pair number 23 –
turner syndrome
•
Tetraploid – 2 extra chromosomes (48)
•
Polyploids – organisms with more than the usual
number of chromosome sets
•
Is rare in animals and almost always results in
death.