Unit 11: genetics & genetic engineering
DNA
DNA stands for deoxyribonucleic acid. It is a chemical made up of two long
molecules, arranged in a spiral. We refer to this as the double-helix structure.
DNA carries genetic information. It is the blueprint of biological guidelines
that a living organism must follow to exist and remain functional. It has all
the instructions that a living organism needs to grow, reproduce, and
function.
Each DNA molecule consists of the following.
Two backbone chains of deoxyribose sugars and phosphate groups.
These backbones are described as antiparallel as they each run in
opposite directions.
Pairs of nitrogenous bases joining the backbones together. The base
pairs join to each other by hydrogen bonds (H bonds). A purine base
always joins with a pyrimidine base, so the ‘rungs of the ladder’ are
always the same size. A join, by two H bonds, with T; G joins, by three
H bonds, with C. This type of specific base pairing is called
complementary base pairing
Sugar phosphate
backbone
Base pair
adenine
Nitrogenous
base
Thymine
Guanine
cytosine
mRna
The primary function of mRNA is to act as an intermediary between the
genetic information in DNA and the amino acid sequence of proteins. mRNA
contains codons that are complementary to the sequence of nucleotides on
the template DNA and direct the formation of amino acids through the action
of ribosomes and tRNA. mRNA also contains multiple regulatory regions which
will determine the timing and rate of translation. additionally, it ensures that
,Unit 11: genetics & genetic engineering
translation proceeds in an orderly fashion because it contains sites for the
docking of ribosomes, tRNA furthermore as various helper proteins
Structurally, mRNA is a linear, single-stranded molecule. A mature mRNA
consists of a coding region, untranslated regions (UTR), 5′ cap, and a 3′ poly-A
tail. The coding region of mRNA contains a series of codons, which are
complementary to the protein-coding genes in the genome. In RNA, the
pentose sugar is ribose
5’ 3’
untranslated Coding untranslated 3’ poly
region region region (A) tail
Initiation Polyadenylation
codon signal
7- methyl GTP “cap”
at 5’-end
tRNA
Transfer RNAs are coded by several genes, and are usually short molecules,
between 70-90 nucleotides (5 nm) in length. The two most important parts of
a tRNA are its anticodon and the terminal 3’ hydroxyl group, which can form
an ester linkage with an amino acid.
Transfer RNAs have a sugar-phosphate backbone like all other cellular nucleic
acids and the orientation of the ribose sugar gives rise to directionality in
the molecule. One end of the RNA has a reactive phosphate group attached
to the fifth carbon atom of ribose while the other end has a free hydroxyl
group on the third carbon atom. This gives rise to the 5’ and 3’ ends of the
RNA since all the other phosphate and hydroxyl groups are involved in
phosphodiester bonds within the nucleic acid.
, Unit 11: genetics & genetic engineering
Amino acid 3’
attachment site OH
Acceptor stem P 5’
T loop
D loop
Variable loop
Anticodon stem
Anticodon loop Wobble
position
anticodon
tRna
rRNA
The rRNA ensures the proper alignment of the mRNA, tRNA, and the
ribosomes; the rRNA of the ribosome also has an enzymatic activity (peptidyl
transferase) and catalyses the formation of the peptide bonds between two
aligned amino acids during protein synthesis.
In rRNA, each ribosome is made of RNA and protein which together form
nucleoproteins. The RNA is the catalyst in ribosomes, enabling protein
assembly.
Structurally Ribosomal RNA is transcribed in the nucleus, at specific
structures called nucleoli. These are dense, spherical shapes that form
around genetic loci coding for rRNA. Nucleoli are also crucial for the eventual
biogenesis of ribosomes, through the sequestration of ribosomal proteins.
The primary structure of rRNA sequences can vary across organisms, base-
pairing within these sequences commonly forms stem-loop configurations.
The length and position of these rRNA stem-loops allow them to create three-
dimensional rRNA structures that are similar across species. The structure of
a ribosome is also determined by the three-dimensional shape of its rRNA
core. rRNA is mainly composed of cellular RNA and is the most
dominant RNA within the cells of all living beings. rRNA is a longer, stable
RNA molecule composing 60% of the mass of the ribosome.
rRNAs combine with proteins in the cytoplasm to form ribosomes, which act
as the site of protein synthesis and has the enzymes needed for the process.
DNA
DNA stands for deoxyribonucleic acid. It is a chemical made up of two long
molecules, arranged in a spiral. We refer to this as the double-helix structure.
DNA carries genetic information. It is the blueprint of biological guidelines
that a living organism must follow to exist and remain functional. It has all
the instructions that a living organism needs to grow, reproduce, and
function.
Each DNA molecule consists of the following.
Two backbone chains of deoxyribose sugars and phosphate groups.
These backbones are described as antiparallel as they each run in
opposite directions.
Pairs of nitrogenous bases joining the backbones together. The base
pairs join to each other by hydrogen bonds (H bonds). A purine base
always joins with a pyrimidine base, so the ‘rungs of the ladder’ are
always the same size. A join, by two H bonds, with T; G joins, by three
H bonds, with C. This type of specific base pairing is called
complementary base pairing
Sugar phosphate
backbone
Base pair
adenine
Nitrogenous
base
Thymine
Guanine
cytosine
mRna
The primary function of mRNA is to act as an intermediary between the
genetic information in DNA and the amino acid sequence of proteins. mRNA
contains codons that are complementary to the sequence of nucleotides on
the template DNA and direct the formation of amino acids through the action
of ribosomes and tRNA. mRNA also contains multiple regulatory regions which
will determine the timing and rate of translation. additionally, it ensures that
,Unit 11: genetics & genetic engineering
translation proceeds in an orderly fashion because it contains sites for the
docking of ribosomes, tRNA furthermore as various helper proteins
Structurally, mRNA is a linear, single-stranded molecule. A mature mRNA
consists of a coding region, untranslated regions (UTR), 5′ cap, and a 3′ poly-A
tail. The coding region of mRNA contains a series of codons, which are
complementary to the protein-coding genes in the genome. In RNA, the
pentose sugar is ribose
5’ 3’
untranslated Coding untranslated 3’ poly
region region region (A) tail
Initiation Polyadenylation
codon signal
7- methyl GTP “cap”
at 5’-end
tRNA
Transfer RNAs are coded by several genes, and are usually short molecules,
between 70-90 nucleotides (5 nm) in length. The two most important parts of
a tRNA are its anticodon and the terminal 3’ hydroxyl group, which can form
an ester linkage with an amino acid.
Transfer RNAs have a sugar-phosphate backbone like all other cellular nucleic
acids and the orientation of the ribose sugar gives rise to directionality in
the molecule. One end of the RNA has a reactive phosphate group attached
to the fifth carbon atom of ribose while the other end has a free hydroxyl
group on the third carbon atom. This gives rise to the 5’ and 3’ ends of the
RNA since all the other phosphate and hydroxyl groups are involved in
phosphodiester bonds within the nucleic acid.
, Unit 11: genetics & genetic engineering
Amino acid 3’
attachment site OH
Acceptor stem P 5’
T loop
D loop
Variable loop
Anticodon stem
Anticodon loop Wobble
position
anticodon
tRna
rRNA
The rRNA ensures the proper alignment of the mRNA, tRNA, and the
ribosomes; the rRNA of the ribosome also has an enzymatic activity (peptidyl
transferase) and catalyses the formation of the peptide bonds between two
aligned amino acids during protein synthesis.
In rRNA, each ribosome is made of RNA and protein which together form
nucleoproteins. The RNA is the catalyst in ribosomes, enabling protein
assembly.
Structurally Ribosomal RNA is transcribed in the nucleus, at specific
structures called nucleoli. These are dense, spherical shapes that form
around genetic loci coding for rRNA. Nucleoli are also crucial for the eventual
biogenesis of ribosomes, through the sequestration of ribosomal proteins.
The primary structure of rRNA sequences can vary across organisms, base-
pairing within these sequences commonly forms stem-loop configurations.
The length and position of these rRNA stem-loops allow them to create three-
dimensional rRNA structures that are similar across species. The structure of
a ribosome is also determined by the three-dimensional shape of its rRNA
core. rRNA is mainly composed of cellular RNA and is the most
dominant RNA within the cells of all living beings. rRNA is a longer, stable
RNA molecule composing 60% of the mass of the ribosome.
rRNAs combine with proteins in the cytoplasm to form ribosomes, which act
as the site of protein synthesis and has the enzymes needed for the process.
