Polymers of nucleotides
Nucleotides are joined in a condensation polymerisation reaction to form polynucleotides.
Water is released and a covalent bond (phosphodiester bond) forms joining the nucleotides together.
LongCoiledDouble-stranded nucleic acidIt forms a double helix.The two strands of DNA are antiparallel. One runs in the 5' to 3' direction, while the other runs in the opposite direction.
How are DNA nucleotides built
Nucleotides are made up of - Deoxyribose sugar - Phosphate - One of four nitrogenous bases (adenine, cytosine, guanine and thymine). The two strands of DNA are joined by complementary base pairing between the nitrogenous bases.
ShortUsually single-stranded Nucleic acid
RNA contains nucleotides that are made up of -Ribose sugar-A phosphate - one of four nitrogenous bases (adenine, cytosine, guanine and uracil).
DNA stores hereditary informationCarrys the instructions that code for the production of mainly proteins but also functional RNA moleculesIt is stored in a specific sequence of nucleotides.
A gene is a region of DNA that codes for a protein or a functional RNA molecule
The role of RNA
To express the information contained in the nucleotide sequence of a gene to synthesise proteins
A single-stranded nucleic acid that carries a copy of the genetic sequence in DNA, specifying the amino acid sequence for a particular protein.
Makes up part of a ribosome. Ribosomes are the sites where the information in the mRNA is translated into a chain of amino acids.
Carry specific amino acids to ribosomes in order to form polypeptide chains
The geneic code
the genetic code is the set of rules about how the instructions carried in nucleic acids are translated to synthesise proteins and functional RNA molecules.
How is the genetic code stored
In DNA this information is stored as a three-letter code of nucleotides known as a triplet.
What are codons?
When these triplets are transcribed into mature mRNA, they are then known as codons.
The genetic code is universal and degenerate. There are 64 possible codons of three nucleotides (e.g. UAC) for the 20 amino acids.
Eukaryotic genes have a number of structural features in common:
- Stop and start instructions —These indicate where transcription starts and stops. Stop codons do not code for amino acids.
- Promoter region—This is the site at which the RNA polymerase attaches to the gene to begin transcription (sometimes called the TATA box).
- Exons—These are the DNA regions that are coding segments.
- Introns—These are the DNA regions that are non-coding segments
What is gene expression?
Gene expression is the process in which the information stored in a gene is used to synthesise a functional gene product (protein or RNA). Gene expression is regulated so that it occurs if and when the particular protein or RNA is required by the cell.
What are the Eukaryote protein synthesis stages?
Protein synthesis in eukaryotes occurs in three stages:
- RNA processing
Eukaryote protein synthesis - Transcription3 steps & 2 points
Transcription occurs in the nucleus and involves RNA polymerase transcribing the DNA into a primary RNA transcript. - During RNA processing in eukaryotes, a 5' cap is added to the 5' end of the primary RNA transcript and a poly-A tail is added to the 3' end. The cap and tail make the mRNA more stable and prevent it from degrading. -Next, the primary RNA transcript is spliced to remove the introns, and someti mes some exons, resulting in mature mRNA. -The mature mRNA then exits the nucleus.
Eukaryote protein synthesis - Translation3 steps
Translation occurs on a ribosome.The codons on mRNA are translated into a sequence of amino acidsThese are delivered by their specifc tRNA molecules, to form a polypeptide chain.
When can Eukaryote gene expresion be regulated
Gene expression in eukaryotes can be regulated at any of the three stages: transcription, RNA processing and translation.
When can Prokaryote gene expresion be regulated
Gene regulation in prokaryotes occurs during transcription.
When are Constitutive genes expressed
Constitutive genes are expressed continually.
Transcription of other genes can be induced or repressed as needed by transcription factors, which is a form of gene regulation.
Regulatory genes code for the production of transcription factors.
Transcription factorsTheir working method
Transcription factors are proteins that control gene expression at the transcription stage. They induce or repress the expression of specifc genes by binding to DNA sequences close to the promoter region of a gene or to the RNA polymerase.
Structural genes code for proteins and RNAs that are not involved in gene regulation; for example, enzymes.
E coli example of transcription regulation
The 'lac operon' in E. coli provides an example of a unit of DNA for which transcription can be induced or repressed—or in other words, regulated. - The regulatory gene lacI constitutively expresses a transcription factor called the lac repressor. - The lac repressor binds to the operator of the lac operon, inhibiting transcription, unless lactose is present. - In the presence of lactose, the lactose binds to the lac repressor, inhibiting it from binding to the lac operon, and enabling the RNA polymerase to bind to the lac operon and begin transcription.
Contrast structure of genetic info between prokaryotes and eukaryotes
There are many diferences in the structure of the genetic information of prokaryotes and eukaryotes, - Prokaryotes have much less DNA but more genes per number of bases than eukaryotes. - Because eukaryotes have much more DNA, they have to package it more tightly. - These structural diferences afect the way in which genetic information is transcribed, translated and expressed.
Similarities of genetic info in prokaryotes and eukaryotes.
The same code of nitrogenous bases (A, T, C, G and U) translates into amino acids and proteins in much the same way in prokaryotes and eukaryotes