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PROTEIN SYNTHESIS:
Transcription & Translation
Protein Synthesis Videos
• http://www.youtube.com/watch?v=41_Ne5mS2ls
• http://www.youtube.com/watch?v=983lhh20rGY&feature=related
I. What are Proteins?
A. Proteins are organic molecules made of various arrangements of 20 amino acids
B. Examples-1. Enzymes.2. Transport proteins and receptor
molecules in cell membranes-ex. hemoglobin
…
3. Hormones- ex. Insulin, adrenaline, testosterone
4. Structural proteins- ex. Keratin and collagen in skin, actin and myosin of muscle.
I. What are Proteins? (con’t)
…
5. Antibodies
6. Storage molecules- ex. Albumin in egg white, casein in milk, and plant proteins in seeds.
I. What are Proteins? (con’t)
REVIEW… AGAIN• Chromosomes are made of DNA • Segments of DNA code for a protein
(Genes) • Protein in turn, relates to a trait (eye
color, enzymes, hormones..)
C. Shape of DNA-twisted ladder
1. Sides of the ladder= sugar + phosphate
2. Rungs (steps) = nitrogen bases
PP
PP
S
S
S
S
S
S
NB
NB
NB
C. Shape of DNA-twisted ladder(con’t)
3. sugar + phosphate are held together by strong covalent bonds
4. nitrogen bases are held together by weak hydrogen bonds
PP
PP
S
S
S
S
S
S
NB
NB
NB
DNA REPLICATION• Replication is the process where DNA
makes a copy of itself. • DNA are instructions to know how to
be a cell. • DNA replicates right before a cell
divides. (In Interphase of Cell Cycle)
E. DNA’s Problem
1. DNA cannot leave the nucleus.2. So, How does it get the instructions to
the ribosome?....… RNA
RNA = ribonucleic acid• RNA is similar to DNA except:
1. Single stranded2. Uracil instead of thymine3. Ribose instead of deoxyribose
• mRNA has the job of taking the message from the DNA in the nucleus to the ribosomes.
• Transcription – (in Nucleus)– RNA is made from DNA’s code(message)
• Translation – (on Ribosome)– Proteins are made from the message on the RNA
B. Types of RNA
1. mRNA- messenger RNA takes DNA’s instruction from the nucleus to the ribosome.
2. tRNA- transfer RNA brings an amino acid from the cytoplasm to the ribosome.
3. rRNA- ribosomal RNA
DNA
mRNA
Transcription
The Central Dogma: Proteins can’t be made back into Nucleic Acids.
Cell
Polypeptide(protein)
TranslationRibosome
Transcription: Protein Synthesis•Transcription is the process by which a molecule of DNA is copied into a complementary strand of RNA. •This is called messenger RNA (mRNA) because it acts as a messenger between DNA and the ribosomes where protein synthesis is carried out.DNA RNA Proteins Transcription Translation
HAPPENING IN NUCLEUS HAPPENING IN CYTOPLASM ON RIBOSOME
Transcription• DNA Strand: T G C A T C A G A• RNA Strand: A C G U A G U C U
• DNA is transcribed into mRNA (messenger RNA)
• mRNA leaves the nucleus and travels to the cytoplasm to find a Ribosome!– In order to use DNA’a message to make a
protein for the body
Transcription process•RNA polymerase (an enzyme) attaches to DNA at a special sequence that serves as a
“start signal”.•The DNA strands are separated at the H-bonds and Nitrogen bases and one strand serves as a template.•The RNA bases attach to the complementary DNA template, thus synthesizing (making)
mRNA.
Transcription process continued
•The RNA polymerase recognizes a termination site on the DNA molecule and releases the new mRNA molecule.(mRNA leaves the nucleus and travels to the ribosome in the cytoplasm.)
1. The DNA strands separate at the H-bonds holding the nitrogen bases together. *An enzyme causes the unwinding.
B. Steps of Transcription:DNA strand
The Nucleus
deoxyribose
phosphate
adenine
thymine
cytosineguanine
ribose
uracil
2. mRNA (messenger RNA) nucleotides in the nucleoplasm then base-pair with the DNA. Another enzyme catalyzes this.
B. Steps of Transcription:DNA strand
The Nucleus
deoxyribose
phosphate
adenine
thymine
cytosineguanine
ribose
uracil
3. The mRNA nucleotides covalently bond to each other between sugars and phosphates.
B. Steps of Transcription:DNA strand
The Nucleus
deoxyribose
phosphate
adenine
thymine
cytosineguanine
ribose
uracil
4. The DNA strands will bond back together.
5. The mRNA chain can now leave the nucleus.
B. Steps of Transcription:DNA strand
The Nucleus
deoxyribose
phosphate
adenine
thymine
cytosineguanine
ribose
uracil
6. Where is mRNA going? ………………………………to a ribosome
B. Steps of Transcription:DNA strand
The Nucleus
deoxyribose
phosphate
adenine
thymine
cytosineguanine
ribose
uracil
Protein Synthesis: Transcription
Transcription
Protein Synthesis: Translation
•Translation is the process of decoding a mRNA molecule’s message from DNA into a polypeptide chain or protein.•Each combination of 3 nucleotides on mRNA is called a codon. •Each codon specifies a particular amino acid that is to be placed in the amino acid chain which makes a protein.
– Ribosomes in the cytoplasm use the code on mRNA to translate it into amino acids
1.How the code is read:a. Every 3 bases on mRNA represents a
code for an amino acid (building block of protein)
b.Every 3 bases on mRNA is called a codon.
c. Amino acids are abbreviated most times by using the first 3 letters of the amino acid’s name.• Met = methonine• Leu = leucine
Reading the Codon Chart
Third Position
First Position
Examples:
AUG = Methionine
CAU = Histidine
UAG = Stop
Try these:
GCU:
UAC:
CUG:
UUA:
Answers:
Alanine
Tyrosine
Leucine
LeucineThis chart only works for mRNA codons.
Slide # 10
Protein Synthesis: TranslationTransfer RNA (tRNA)•Each tRNA molecule has 2 important sites of attachment.
•One site, called the anticodon, binds to the codon on the mRNA molecule.
•The other site attaches to a particular amino acid.
•During protein synthesis, the anticodon of a tRNA molecule base pairs with the appropriate mRNA codon.
Protein Synthesis: Translation
•The protein chain (amino acids) continues to grow.
• Until a stop codon reaches the ribosome•Which results in the release of the new protein and mRNA, completing the process of translation. • Amino acids form a chain =
a protein
STEPS OF TRANSLATION1. The mRNA travels to the cytoplasm 2. Amino acids exist freely in the cytoplasm, many of them you acquire from your diet3. Each 3 bases of mRNA (codon) translates (has a message to make a single amino acid.)4. The ribosome looks for the "start" codon - AUG, this is where the chain begins5. Transfer (tRNA), has an anticodon at one end and an amino acid at the other, it binds to a complementary codon.
6. Another tRNA reads the next codon, the amino acid attached to it binds with the amino acid on the previous tRNA using a peptide bond. The first tRNA falls off.7. This process continues until the "stop" codon is reached.8. The amino acid chain folds into a 3 dimensional structure, now a protein.9. That protein can be an enzyme, a hormone, or any other structure in the body that gives it traits and functionality.
mRNA
t RNA
mRNA
Start codon
Ribosome
Methionine
PhenylalanineLysine
Nucleus
Translation
Go to Section:
Anticodon
Slide # 12
The Polypeptide “Assembly Line”
mRNARibosome
Translation direction
Lysine tRNA
tRNA
Ribosome
Growing polypeptide chain
mRNA
Completing the Polypeptide
Translation
Go to Section:
Slide # 13
nucleus
ribosome
codon
mR
NA
mRNAcodoncodoncodon
AA AU
U
U U UC C C
G G
cytoplasm
nucleus
ribosome
codon
mR
NA
mRNA
tRNA
anticodon
codoncodoncodon
A
A
A
A
AU U U U
U
C C C
C
G
G
G
cytoplasm
START
nucleus
ribosome
codon
mR
NA
mRNA
tRNA tRNA
anticodon
codoncodoncodon
A
A
A AU U U U
G
C C C
G
G G
cytoplasm
proline START
nucleus
ribosome
codon
mR
NA
mRNA
tRNA
anticodon
codoncodoncodon
AA
A
AU
U
U U UC
C
C CG G
cytoplasm
prolinevaline START
nucleus
ribosome
codon
mR
NA
mRNA
tRNA
anticodonanticodon
codoncodoncodon
AA
A A
A
U
U U U UC C C
G
G
G
cytoplasm
prolinevalineleucine START
cytoplasm
Translation
DNA TRANSLATIONtRNA translates mRNA into proteins
SUMMARY
Mutation
Any mistake or change in DNA sequenceTYPES:
SubstitutionA substitution is a mutation that exchanges one base for another (i.e., a change in a single "chemical letter" such as switching an A to a G).
InsertionInsertions are mutations in which extra base pairs are inserted into a new place in the DNA.
•DeletionDeletions are mutations in which a section of DNA is lost, or deleted
Frameshift
Since protein-coding DNA is divided into codons three bases long, insertions and deletions can alter a gene so that its message is no longer correctly parsed.
These changes are called frameshifts. For example, consider the sentence, "The fat cat sat." Each word represents a codon. If we delete the first letter and parse the sentence in the same way, it doesn't make sense.
Mutagen
Any agent capable of altering a cell’s genetic makeup (DNA); causes a mutation
Examples:Cosmic raysX-raysUV lightSome chemicals
Mutations and Genetic Disorders
1.Most genetic disorders result from a mutation in one gene.a.Mutation: a change in an
organism’s genetic material (DNA)
2.A mutated gene produces a flawed protein that does not function properly or a protein that does not function at all.a.Examples of genetic disorders
that are caused by the mutation of one gene: Hemophilia, sickle cell anemia, and cystic fibrosis.
Introduction to Mutations
Normal blood cells
Sickle-shaped blood cells
Slide # 2
Causes of Mutations
1.Mutagens: environmental factors that can cause some mutations
2.Examples of mutagens:a.UV radiationb.Pollutionc.Certain chemicalsd.Viruses
UV radiation can cause mutations.
Viruses can cause mutations.
Slide # 3
Gamete (Germ line) Cell Mutations1.If mutations occur in gametes or the cells that
produce gametes, then these mutations can be transmitted to future generations.
2.This mutation will be found in every cell of the offspring’s body.
Slide # 4
Body (Somatic) Cell Mutations
1. Mutations in any body cell like skin can not be passed on to offspring.
Slide # 5
Gene Mutations Caused by Point Mutation
Go to Section:
1. Point mutations : one base is replaced with the wrong base (letter)
2. Also called Base-Pair Substitutions
3. Example: Sickle-cell anemia
Slide # 6
Point Mutations: Silent Gene Mutations
Go to Section:
1.Silent mutation: a base is changed, but the new codon codes for the same amino acid. ( typically it is the third letter in the codon)
Slide # 7
Original
mRNAProtein
leading to a silent mutation
Point Mutations: Missense Mutations
Go to Section:
1.Missense Mutations: point mutation that still codes for an amino acid, just the wrong amino acid
2. May or may not be harmful
Slide # 8
Original
mRNAProtein
Nonsense
mRNAProtein
Point Mutations: Nonsense Mutations
Go to Section:
1.Nonsense mutations: prematurely code for a stop codon
2. Result: a nonfunctional protein
Slide # 9
Original
Deletion
Gene Mutations: Deletion
Go to Section:
1.Deletion: one or more of the bases is deleted from the code
2. Causes a shift in the reading frame
3. Usually ends up causing a missense or a nonsense mutation.
Slide # 10
Insertion
Gene Mutations: Insertion
Go to Section:
1.Insertion: one or more base pairs are inserted into the code
2. Causes a shift in the reading frame
3. Usually ends up making a missense or a nonsense mutation.
Slide # 11
Chromosomal Mutations
Go to Section:
Slide # 12
1. Usually happens during meiosis (crossing over errors in gamete production)
2. Deletion: part of the chromosome is lost (whole genes are lost)
Chromosomal deletion video
Deletion of Gene B
Chromosomal Mutations
Go to Section:
Slide # 12
3. Duplication: part of a chromatid breaks off and attaches to the other sister chromatid (whole genes are repeated)
Chromosomal duplication video
Duplication of Gene B
Inversion of Genes BCDE
Chromosomal Mutations
Go to Section:
Slide # 12
4. Inversion: when a piece of a chromosome breaks off and is flipped backwards before it reattaches (genes are rearranged on the same chromosome)
Chromosomal inversion video
Translocation of DEF with JKL
Chromosomal Mutations
Go to Section:
Slide # 12
5. Translocation: when part of 1 chromosome breaks off and attaches to a different chromosome (chromosomes end up with different genes)
Chromosomal translocation video
Deletion
Duplication
Inversion
Translocation
Chromosomal Mutations
Go to Section:
Slide # 12
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