Transcript Synthesis and Release of Protein

Synthesis and Release of
Protein
Mr G Davidson
Variety of Protein
• Proteins are important molecules in
biology.
• They contain the elements Carbon,
Hydrogen, Oxygen and Nitrogen.
• They often contain Sulphur and
Phosphorous.
Tuesday, 07 July 2015
G Davidson
Slide 2
Variety of Protein
• Proteins are built from chains of amino acids,
held together by peptide bonds forming
polypeptides.
• If the polypeptides form parallel strands,
fibrous proteins are formed, and if they
become tangled up to form a spherical shape,
globular proteins are formed.
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G Davidson
Slide 3
Variety of Protein
• Proteins form many different parts of an
organism and have many functions.
• e.g. -enzymes, antibodies, structural,
hormones,
etc.
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G Davidson
Slide 4
Structure of DNA
• Cell proteins are built according to
inherited information held in the nucleus,
the information is packaged as
chromosomes.
• The chromosomes are made up of chains of
molecules, called genes.
• A gene is a unit of heredity and is
composed of a complex substance called
Deoxyribonucleic acid.
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G Davidson
Slide 5
Structure of DNA
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G Davidson
Slide 6
Structure of DNA
Phosphate
Deoxyribose
sugar
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G Davidson
Slide 7
Structure of DNA
• The DNA molecule can be described
as a double helix.
• It is made up of two strands of subunits called nucleotides.
• Each nucleotide has 3 parts:
– deoxyribose sugar
– a base
– phosphate
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G Davidson
P
Ribose
sugar
Base
Slide 8
Structure of DNA
• There are four
different nucleotides,
because there are
four different bases.
• The four bases are:
–
–
–
–
Cytosine
Guanine
Adenine
Thymine
P
Ribose
Cytosine
P
Ribose
Guanine
P
Ribose
Adenine
P
Ribose
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G Davidson
Thymine
Slide 9
Structure of DNA
• The molecule is held together in two
different ways.
• A strand is connected by strong bonds
between the sugar and phosphate.
• The strands are held together by weak
hydrogen bonds connecting cytosine to
guanine and adenine to thymine.
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G Davidson
Slide 10
DNA Replication
•
•
During cell division, the genes must be
able to replicate in order that each new
cell gets a full chromosome compliment.
In order for replication to occur, the
following must be present in the nucleus
of the cell:
1.
2.
3.
4.
a supply of nucleotides (4 types)
ATP
a DNA molecule to copy
appropriate enzymes
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G Davidson
Slide 11
DNA Replication
•
•
•
Replication begins with the uncoiling of
the DNA helix.
Once this has happened, the weak
hydrogen bonds joining the two strands
break, causing the DNA molecule to
‘unzip’.
Once the bases are exposed, free
nucleotides find their complimentary
bases, forming two new DNA molecules,
identical to the original molecule.
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G Davidson
Slide 12
DNA Replication
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G Davidson
Slide 13
Protein Synthesis
• The sequence of bases along a strand
of DNA is anything but random.
• The order of bases is called the
genetic code.
• The code is actually a ‘recipe’ for
protein production.
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G Davidson
Slide 14
Protein Synthesis
• Proteins are chains of amino acids of which
there are twenty in nature , so it follows
that the DNA code should be able to
specify at least 20 different items.
• To do this, the bases of DNA are grouped
in threes, these are called triplets of
bases, each containing a triplet code for a
specific amino acid.
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G Davidson
Slide 15
Protein Synthesis
• DNA occurs in the nucleus of a cell, and
protein synthesis on the ribosomes in the
cytoplasm, therefore something must
happen which transfers information from
one place to another.
• Protein synthesis occurs in two stages:
-transcription
-translation
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G Davidson
Slide 16
Transcription
• The information contained in the DNA code
has to be collected and taken out of the
nucleus and this is done by another nucleic
acid called Ribonucleic Acid (RNA).
• It is similar to DNA except:
1. it is a single strand
2. it has a ribose rather than a deoxyribose sugar
3. the base Thymine is changed to the base Uracil
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G Davidson
Slide 17
Transcription
• There are two types of RNA
1. messenger RNA
2. transfer RNA
(mRNA)
(tRNA)
• During protein synthesis, the appropriate
region of DNA temporarily opens up to
expose the bases to produce a strand of
mRNA which then leaves the nucleus
through the pores.
• The mRNA template is made of triplet
bases called codons.
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G Davidson
Slide 18
Translation
• Once the mRNA leaves the nucleus, it
becomes attached to a ribosome.
• In the cytoplasm, there are still
tRNA molecules containing only 3
bases called an anticodon, which
corresponds to a specific amino acid.
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G Davidson
Slide 19
Translation
• The codons of the mRNA pair up with
the anticodons of the tRNA which is
carrying an amino acid.
• The amino acids are then joined
together by peptide bonds to form
proteins.
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G Davidson
Slide 20
Protein Synthesis
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G Davidson
Slide 21
Protein Secretion
• Many of the enzymes and other proteins
made by the cell will have to be secreted
by the cell since they may be used in
remote parts of the organism.
• These proteins are processed by the Golgi
body where carbohydrates are added to
form glycoproteins.
• These are then pinched off to produce
vesicles which are then transported to the
plasma membrane where they are secreted.
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G Davidson
Slide 22
Protein Secretion
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G Davidson
Slide 23