- DNA does not synthesize proteins by itself Portions of DNA sequence are transcribed into RNA
- Nucleotide sequence of the appropriate segment of DNA is copied
- The process of making RNA from gene (the functional segment of
to be transcribed to RNA
DNA) is called transcription because it is still written in the same
- The resulting RNA is translated into proteins
language of nucleotides (only a section of DNA, the gene is
- This is a fundamental principle, termed the central dogma which
transcribed, not the whole genome)
states that the flow of info is only in one direction, from DNA, to
- RNA is a linear polymer of 4 different nucleotide subunits (adenine,
RNA, to protein; or from RNA to protein
uracil, cytosine, and guanine)
- 2/3 of the genes are transcribed into protein
- RNA differs from DNA in 2 aspects:
- tRNA and rRNA are not translated into proteins
- The nucleotides are ribonucleotides because their sugar is ribose
- some RNA gets deleted immediately after translation
sugar
- In eukaryotes transcription takes place inside the nucleus and
- Instead of the base thymine, there is uracil, and it bonds in the same
translation takes place outside the nucleus
manner as A-T
- In prokaryote both take place at the same time in same region
- There are major differences in overall structures of DNA and RNA
- After translation, not all polypeptides are functional
- RNA is single stranded
- Even if they are functional and form an amino acid, they might be
- This allows RNA to fold into a variety of shapes
turned off
- The ability of RNA to fold into a complex 3D shape allows it to carry
From DNA to RNA out various functions such as structural, regulatory, and catalytic
roles
- Identical copies of many RNA can be transcribed from the same
- tRNA are about 80 nucleotides long
gene to make many of the same protein
- Allows cell to rapidly make large amounts of proteins
- Transcription and translation can take place at different rates to
allow cells to make vast amounts of some proteins and small
amounts of other
- DNA double helix is opened and only one of the strands is used as
the template
- The template strand is called the nonsense strand but the non
template strand is called the sense strand and the coding strand
- The nonsense/template strand is the one copied to be translated
into RNA
- Transcription happens from 5’ to 3’
- The ribonucleotides come as rNTPs and then are phosphorylated
- The RNA strand does not stay bound to the DNA template; the
strand instantly falls off as primase makes it
, Transcription produces RNA that is complementary to one strand of DNA Cells produces various types of RNA
- RNA is made by transcription - mRNA are the RNAs that direct the synthesis of proteins
- Transcription begins by unwinding a section of DNA to expose the - in eukaryotes, mRNA carry info from a single gene that codes for a
bases single protein
- One strand of the DNA acts as a template - in bacteria, more than one gene is used to transcribe a mRNA which
- Ribonucleotides are added in the same fashion as nucleotides, if it is therefore carries info for more than 1 protein
a good match, RNA polymerase covalently bonds the ribonucleotide - however, some final products of genes are RNA itself
to the DNA base - these RNAs are tRNA, rRNA, miRNA and other noncoding RNAs
- It is complimentary to the DNA template - they are responsible for several roles such as serving as regulatory,
- Unlike DNA daughter strands, RNA does not stay hydrogen bonded structural, and catalytic components of the cells
to the template strand - rRNAs form the structural and catalytic core of the ribosomes which
- As soon as the RNA is separated, DNA double helix binds again translate mRNAs into proteins
- Due to this and the fact that only one strand is used as a template, - tRNAs act as adaptors that select specific amino acids and hold
RNA is single stranded them in a place on a ribosome for their incorporation into protein
- RNA is also shorter because only a small section of DNA is - miRNA act as key regulators of eukaryotic gene expression
transcribed - gene expression refers to the process by which info in a DNA
- DNA molecules can be up to 250 million nucleotide pair long, but sequence is translated into a product that has some effect on a cell
RNA is no more than 1000 nucleotides long or organism
- RNA polymerase catalyzes the formation of the phosphodiester - gene expression includes both translation and transcription
bond and forms the sugar phosphate backbone of the RNA chain
signals in DNA tell RNA polymerase where to start and finish
- The polymerization takes place in 5’ to 3’ direction
transcription
- Ribonucleoside triphosphates provide the energy needed for the
reaction to take place - In bacteria, initiation of transcription takes place when RNA
- The immediate release of the RNA molecule allows many RNA to be polymerase collides with a DNA molecule and stick firmly to the
synthesized form the same gene in a very short time; synthesis can double helix and then slides rapidly along its length
begin before the other RNA is made - When it finally encounters a sequence region called the promoter, it
- it takes approx. 50 seconds for a 1500 nucleotide to be transcribed latches more tightly
- more than 1000 transcripts can be synthesized in an hour - Then the RNA polymerase unwinds the double helix to expose the
- RNA polymerase uses ribonucleoside for phosphates as substrates, base
so it does catalyzation of ribonucleotides - Two ribonucleoside triphosphates are joined together by
- RNA transcription can begin without a primer because it does not polymerase to begin synthesis of the RNA chain
need to be very accurate as it is not used as a permanent storage - Chain elongation takes place until polymerase encounters the
form of genetic info terminator
- RNA polymerase makes 1 mistake every 10^4 nucleotides - The terminator sequence is transcribed in the 3’ end of the RNA
transcribed chain polymerised; the terminator sequence is transcribed into the
RNA transcript too
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