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

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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