Download DNA – Deoxyribose Nucleic Acid

DNA – Deoxyribose Nucleic Acid
1. DNA is composed of a chain
of nucleotides, each made up of
a sugar group, a phosphate group,
and a nitrogenous base.
2. The phosphate groups of one
nucleotide bind to the sugar group
of the next nucleotide to build a
sugar-phosphate backbone.
3. The nitrogenous bases of DNA
include the pyrimidines Thymine
and Cytosine, and the Purines
Adenine and Guanine.
DNA – Deoxyribose Nucleic Acid
The basic structure of the DNA
is that of two chains of nucleotides
attached to each other in form of a
ladder. This ladder is then twisted
into a spiral, forming a double helix.
DNA – Deoxyribose Nucleic Acid
1. Note that the sugar-phosphate are on the outside of the double helix
2. The nucleotides are very specific to each other, with Adenine and Thymine always binding to each
other, and Guanine and Cytosine always binding to each other.
3. Also note that the sugar-phosphate chains run in opposite direction. This will later become important
in DNA replication
DNA replication
DNA replication Depends on specific base pairing
The DNA untwists, and each
chain is replicated
DNA replication
DNA can only be replicated in only one direction, but remember
that the chains of the DNA went in different directions
DNA polymerase, the enzyme responsible for replicating DNA,
can only add nucleotides to the 3’ (three prime) end of the strand
This basic characteristic of DNA polymerase results in continuous
and segmented replication of the DNA
DNA Replication – Continuous vs. Segmented Replication
DNA Replication – Continuous vs. Segmented Replication
DNA Replication – Continuous vs. Segmented Replication
DNA Replication – Continuous vs. Segmented Replication
Errors in DNA replication?
Mutations can be in form of deletions, additions, and/or change of nucleotide types.
Errors are usually very few – a type of DNA polymerase is involved in proof-reading
and repair of mistakes. Final errors are usually about
one in a billion.
DNA polymerases and DNA ligases are also involved in repairing DNA damage
from harmful radiation (e.g. UV) and/or toxic chemicals in the environment.
Not all mutations that remain un-checked will have an effect on the protein product.
Over evolutionary time, mutations are however a major source genetic variation.
If it were not for mutations, none of the different life forms we see on earth today
would exist.
RNA – Ribose Nucleic Acid
Like DNA, RNA is also a made up of a chain of nucleotides.
Unlike DNA however, the sugar group is a ribose instead of a deoxyribose.
RNA forms single strands instead of the double strands formed by DNA
In the RNA, the nitrogenous base Thymine normally found in the DNA
is replaced by Uracil.
RNA – Ribose Nucleic Acid
Cells have three types of RNA: messenger RNA, transfer RNA, and ribosomal RNA
The different forms of RNA are involved in the transcription and translation of genetic information
Transcription
Transcription
Transcription
Translation
Once the genetic message has been
transcribed onto the mRNA, the tRNA
has the ability to use anticodons to
translate the information into form
of amino acid sequences.
Note that the transcription occurs in
the nucleus, but the translation occurs
in the cytoplasm.
The proteins produced then go on to
carry out all the functions of the cell.
Translation
Translation
Translation
Translation
Regulation of Gene Expression
1. Cells regulate rate of transcription.
2. Cells regulate rate of translation.
3. Cells regulate protein activity by modifying the proteins.
4. Cells regulate protein activity through degradation.