build a protein

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23 Οκτ 2013 (πριν από 3 χρόνια και 8 μήνες)

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Protein Synthesis


Using DNA information to
build a protein

Two Processes:

Transcription



making a copy of DNA’s protein
synthesis information


Translation



using this information to build a new
polypeptide (protein)


AND


RNA



a new participant in the process



The 3 types of RNA


Messenger RNA (mRNA)


Produced in the nucleus from DNA template


Carries genetic message to ribosomes


Transfer RNA (tRNA)


Produced in the nucleus from DNA template


Transfers amino acids to ribosomes


Each type carries only one type of amino acid


Ribosomal RNA (rRNA)


Produced in the nucleolus of the nucleus from DNA template


Joins with proteins to form ribosomes


Ribosomes may be free or in polyribosomes (clusters) or attached to
ER

Figure 11.17 Summary of Protein Synthesis in eukaryotes

Copyright
©
The McGraw
-
Hill Companies, Inc. Permission required for reproduction or display.

ami no

aci ds

l arge and smal l

ri bosomal subunits

DNA

Transcri ption

1. DNA i n nucl eus

serves as a templ ate.

Figure 11.17 Summary of gene expression in eukaryotes

Copyright
©
The McGraw
-
Hill Companies, Inc. Permission required for reproduction or display.

ami no

aci ds

l arge and small

ri bosomal subunits

mature

mRNA

pri mary

mRNA

DNA

Transcription

i ntrons

1. DNA i n nucleus

serves as a template.

2. Pre
-

mRNA i s

processed

before l eaving

the nucleus.

Figure 11.17 Summary of gene expression in eukaryotes

Copyright
©
The McGraw
-
Hill Companies, Inc. Permission required for reproduction or display.

ami no

aci ds

l arge and small

ri bosomal subunits

mature

mRNA

pri mary

mRNA

DNA

Transcription

i ntrons

1. DNA i n nucleus

serves as a template.

2. Pre
-

mRNA i s

processed

before l eaving

the nucleus.

mRNA

3. mRNA moves i nto

cytopl asm and becomes

associated with

ri bosomes.

Figure 11.17 Summary of gene expression in eukaryotes

Copyright
©
The McGraw
-
Hill Companies, Inc. Permission required for reproduction or display.

amino

acids

large and small

ribosomal subunits

mature

mRNA

primary

mRNA

DNA

Transcription

introns

1. DNA in nucleus

serves as a template.

2. Pre
-

mRNA is

processed

before leaving

the nucleus.

mRNA

3. mRNA moves into

cytoplasm and becomes

associated with

ribosomes.

4. tRNAs with

anticodons

carry amino

acids to mRNA.

anticodon

tRNA

Figure 11.17 Summary of gene expression in eukaryotes

Copyright
©
The McGraw
-
Hill Companies, Inc. Permission required for reproduction or display.

5. Anti codon

codon

compl ementary base

pai ring occurs.

ami no

aci ds

l arge and small

ri bosomal subunits

mature

mRNA

pri mary

mRNA

DNA

Transcription

i ntrons

1. DNA i n nucleus

serves as a template.

2. Pre
-

mRNA i s

processed

before l eaving

the nucleus.

mRNA

Translation

3. mRNA moves i nto

cytopl asm and becomes

associated with

ri bosomes.

4. tRNAs with

anti codons

carry ami no

aci ds to mRNA.

anti codon

tRNA

peptide

codon

ri bosome

Figure 11.17 Summary of gene expression in eukaryotes

Copyright
©
The McGraw
-
Hill Companies, Inc. Permission required for reproduction or display.

5. Anticodon

codon

complementary base

pairing occurs.

amino

acids

large and small

ribosomal subunits

mature

mRNA

primary

mRNA

DNA

Transcription

introns

1. DNA in nucleus

serves as a template.

2. Pre
-

mRNA is

processed

before leaving

the nucleus.

mRNA

Translation

3. mRNA moves into

cytoplasm and becomes

associated with

ribosomes.

4. tRNAs with

anticodons

carry amino

acids to mRNA.

anticodon

tRNA

6. Polypeptide

synthesis takes

place one amino

acid at a time.

peptide

codon

ribosome

Figure 11.17 Summary of gene expression in eukaryotes

Copyright
©
The McGraw
-
Hill Companies, Inc. Permission required for reproduction or display.

7. When a ribosome

attaches to rough ER,

the polypeptide enters

its lumen, where the

polypeptide folds and

is modified further.

5. Anticodon

codon

complementary base

pairing occurs.

amino

acids

large and small

ribosomal subunits

mature

mRNA

primary

mRNA

DNA

Transcription

introns

1. DNA in nucleus

serves as a template.

2. Pre
-

mRNA is

processed

before leaving

the nucleus.

mRNA

Translation

3. mRNA moves into

cytoplasm and becomes

associated with

ribosomes.

4. tRNAs with

anticodons

carry amino

acids to mRNA.

anticodon

tRNA

6. Polypeptide

synthesis takes

place one amino

acid at a time.

peptide

codon

ribosome

Figure 11.14 Polyribosome structure and function

Copyright
©
The McGraw
-
Hill Companies, Inc. Permission required for reproduction or display.

5
'

3
'

mRNA

×
400,000

b.

a.

codon

(b): Courtesy Alexander Rich


Summary of Protein Synthesis

1.
Transcription


of DNA information onto a mRNA
molecule

2.
mRNA processing
-

the mRNA molecule is cut so
only the important parts leave the nucleus

3.
mRNA leaves nucleus & travels to ribosomes in
cytoplasm

4.
At the ribosome tRNA is attracted to its mRNA
complements where it is translated into a new
polypeptide (protein)

What is the Genetic Code


We know of 20 amino acids that comprise all known
proteins


DNA information tells the cells which amino acids &
their order (spelling) to use when building a specific
protein


Genetic Code = every three nucleotides equals a
single amino acid
(so if a polypeptide was made of 100 amino
acids, it’s DNA code would be 300 nucleotides long)


Many synonyms exist as well as start & “stop” signs



The genetic code


Translates from nucleic acids to amino acids


Triplet


3 nucleotide sequence in DNA


Codon


3 nucleotide sequence in mRNA


A codon encodes a single amino acid


Start and stop codons


Codons (mRNA)

What Can Go Wrong?

Protein Synthesis
:


Gene mutation


Change in the sequence of bases in a gene


Causes


Replication error


Rare due to proofreading


Transposons


“Jumping genes”


pieces of DNA that move within and
between chromosomes


Mutagens


Environmental influences


radiation


Chemical mutagens


Repair enzymes


Types and effects of mutations


Many mutations go undetected


no observable
effect


Others kill the cell


we have many to spare


Point mutations


Change in single DNA nucleotide Results can be minor or
severe (for example
-

Sickle cell)


Frameshift mutations


Extra or missing nucleotides


Usually much more severe


All downstream codons affected


THE
C
AT ATE THE RAT


C removed


THE ATA TET HER AT


11.3 DNA Technology


Genetic engineering


inserting cloned
genes into an organism


Transgenic organism


Cloning genes


making identical copies


Because the genetic code is nearly
universal, it’s possible to transfer cloned
genes between virtually any organism


Human insulin made by bacterial cells


Human gene removed


Inserted into plasmid


Plasmid inserted into bacteria


Bacteria produce insulin as if it was one of
their own gene products

Figure 11.19 Recombinant DNA technology

Copyright
©
The McGraw
-
Hill Companies, Inc. Permission required for reproduction or display.

cut with

restriction

enzyme

recombinant DNA

add DNA ligase

plasmid DNA

insulin gene

bacterial host cell

human cell

plasmid DNA

insulin

gene

Figure 11.19 Recombinant DNA technology, continued

Copyright
©
The McGraw
-
Hill Companies, Inc. Permission required for reproduction or display.

© SIU/Visuals Unlimited


recombinant DNA

bacterial host cell

cell multiplies;

produces insulin

insulin

insulin

cloned genes for insertion

into another host cell


Transgenic organisms


Biotechnology


use of natural biological systems to create a
product


Organisms can be genetically engineered for use in biotechnology


Transgenic bacteria


Grown in bioreactors


Gene product collected from growth medium


Transgenic plants and animals


Cotton, corn, and potato make their own insecticide


Soybeans herbicide resistant


Larger fishes, cows, and pigs from inserted growth hormone gene


“Pharming”


use of transgenic farm animal to produce pharmaceuticals
in milk


Transgenic animals may be cloned


nucleus from adult cell introduced
into enucleated egg cell produces identical genotype of adult donor


Copyright
©
The McGraw
-
Hill Companies, Inc. Permission required for reproduction or display.

Figure 11.22 DNA fingerprinting

suspect

B

Collect

DNA

crimescene

evidence

suspect

A

Perform

PCR on

repeats

marker

Suspect B

Suspect A

Use gel electrophoresis to identify criminals

Crime

scene

16 repeats

16 repeats

12 repeats

12 repeats

12 repeats

12 repeats

11.4 Genomic and Proteomics


Genomics


study of genomes


Human and other organisms


Coding and noncoding segments


Human Genome Project


13
-
year effort


Found many small regions of DNA vary among individuals


Some individuals even have extra copies of genes


Differences may have no effect or may increase or
decrease susceptibility to disease.