This document discusses RNA synthesis or transcription. It begins by describing RNA and its role in carrying genetic information from DNA to ribosomes for protein synthesis. It then explains how RNA differs from DNA in being single-stranded, linear, and containing uracil instead of thymine. The document goes on to define transcription as the process of copying a gene segment from DNA into messenger RNA (mRNA) in the nucleus, which then transports the information to the cytoplasm to direct protein synthesis at ribosomes. In addition, it mentions two other types of RNA: transfer RNA (tRNA) carries amino acids to ribosomes, and ribosomal RNA (rRNA) makes up ribosomes.

1. RNA Synthesis or “Transcription”
By
Prachee Rajput

2. RNA (Ribonucleic acid)
• RNA is the nucleic acid
that acts as a
messenger between
DNA and the ribosomes
and carries out the
process by which
proteins are made from
amino acids

3. How RNA is Different
from DNA
•Single strand
•Linear not helical
•Contains uracil instead of
thymine
•Copy of 1 gene, not entire DNA
strand (100’s of genes)
•Formed in nucleus prior to
protein synthesis
•Initially in the nucleus BUT then
migrates to cytoplasm via a
nuclear pore and eventually
attaches to a ribosome

4. Transcription
• The process by which a
gene segment of DNA is
copied into a
complementary strand of
RNA
• The type of RNA formed in
this way is called messenger
RNA or mRNA
• Occurs so that the
information to make a
protein can be taken from
the nucleus to the ribosome
where protein synthesis
occurs

5. There are two other types of RNA:
• Transfer RNA (tRNA):
carries amino acids (the
building blocks of
proteins) to the
ribosome where they
can be bonded together
• Ribosomal RNA (rRNA) :
small organelle (the
ribosome) is made of
this kind of rRNA and
proteins. The ribosome
supplies the site where
the reaction to link
amino acids together
occurs.

6. Lets take a closer look at the steps to
make mRNA or transcription:
1) The enzyme RNA
polymerase attaches
to the DNA strand and
unzips it at the gene to
be copied
- “unzipping” means that
the H-bonds between
nitrogenous bases are
broken

7. 2) RNA nucleotides base
pair with the exposed
bases of the gene
being copied
- since 2 sides of the DNA
strand are exposed,
the side being copied
is called the “sense”
side, while the other
uncopied side is called
the “missense” side.

8. 3) Sugar-phosphate
bonds form between
RNA nucleotides
4) Hydrogen bonds break
and mRNA is free to
leave the nucleus
(through a pore) and
attach to ribosome in
the cytoplasm (protein
used in cell) or on RER
(proteins used outside
cell)

9. • Finally, the H-
bonds reform
between the DNA
strands and the
strands rezip.
• http://www.youtube.com/watch?v=ztPkv7wc3yU&featur

10. A sequence…
• Can refer to either the
order the nitrogenous
bases come in on a DNA
strand or mRNA strand
OR the order of the
amino acids in a
polypeptide chain.

11. The sequence of nitrogenous bases on
an mRNA strand is read in a specific
way…
• Each group of 3
nucleotides codes for
one amino acid
• This group of 3
nucleotides is called a
codon
• There are 20 different
amino acids that the
bases code for

12. • Since there are 64
possible
combinations of 3
nucleotides, each
amino acid is coded
for by more than one
codon!
• AUG is the “start”
codon as it shows the
ribosome where to
start protein
synthesis
• There are 3 “stop”
codons that signal the
end of protein
synthesis.

13. Closer look at tRNA
• This molecule “reads” the
genetic code on the mRNA
molecule and supplies the
correct amino acids
• One end holds the amino
acid, the other contains the
“anticodon” that matches
up with the codon on the
mRNA strand

14. Anticodon…
• Each tRNA molecule
contains 3 nucleotides
on one end
• These nucleotides base
pair with a codon on
mRNA, ensuring that
the appropriate amino
acid is added to the
polypeptide chain