Download Unit 5: Genetics

Unit 5: Genetics
Learning Goal 4: Describe how
DNA is used by cells to produce
proteins.
RNA (Ribonucleic Acid)
 RNA
vs. DNA
 Both
consist of long
chains of nucleotides.
 Three main differences:
 RNA
sugar is ribose.
 RNA is generally singlestranded.
 RNA contains uracil in
place of thymine.
Types of RNA
Types of RNA
 Messenger

Carries copies of instructions for assembling amino
acids into proteins to ribosomes.
 Ribosomal

RNA (rRNA)
A form of RNA that makes up ribosomes.

Ribosomes are also made up of several dozen proteins.
 Transfer

RNA (mRNA)
RNA (tRNA)
Transfer each amino acid to the ribosomes as it is
specified by coded messages in mRNA.
Transcription
 The
process of forming RNA
molecules by copying part of the
nucleotide sequence of DNA into a
complementary sequence in RNA.
Transcription



Requires RNA polymerase to bind to the
DNA and separate the DNA strands.
RNA polymerase then uses one strand of
DNA to use as a template.
“Promoters” are areas on a DNA
molecule that an RNA polymerase enzyme
will attach.


These “promoters” have specific base pairs.
Similar signals in DNA cause transcription
to stop.
RNA editing
•
Introns


Exons


Areas of the DNA
molecule that are not
involved in coding for
proteins.
DNA sequences that
code for proteins.
Before mRNA is
complete the introns
must be cut out and
the remaining exons
spliced together.
The Genetic Code

Four different bases.





A= Adenine
U= Uracil
C= Cytosine
G= Guanine
Read by Codons



Three consecutive
nucleotides that specify a
single amino acid that is to be
added to the polypeptide.
64 possible codons.
Start and Stop codons
Codons = Amino Acids
Translation
Translation
1.
2.
3.
mRNA is transcribed in the nucleus and
released into the cytoplasm where it
attaches to a ribosome.
tRNA carries each amino acid to the
ribosome where they attach to one
another according to the genetic code
forming a polypeptide (protein chain).
The process continues until the ribosome
reaches one of the three stop codons.
The result is a complete polypeptide.
Translations
Genes and Proteins
 Genes
contain nothing more than
instructions for assembling proteins.
 Many proteins are enzymes, which
catalyze and regulate chemical reactions.
 Causing
certain things to be produced such
as pigment.
 Proteins
are specifically designed to build
or operate a component of a living cell.