DNA, Genes And Proetein Synthesis Flashcards
DNA In Prokaryotic Cells?
(E.g. bacteria), the DNA molecules are shorter,
They form a circle,
They are not associated with protein molecules,
They do not have chromosomes,
The DNA is condensed to fit in the cell by supercoiling.
DNA In Eukaryotic Cells?
Eukaryotic cells include animal and plant cells.
The DNA molecules are longer and have to be wound up around histones (proteins) so they fit in nucleus,
They form a line (linear) and exist as chromosomes,
They occur in association with proteins called histones to form structures called chromosomes,
The mitochondria and chloroplasts of eukaryotic cells also contain DNA which, like the DNA of prokaryotic cells, is short, circular and not associated with proteins,
DNA is in the nucleus.
What Is mRNA?
Messenger ribonucleic acid.
This mRNA transfers the DNA code from the nucleus to the cytoplasm.
mRNA is small enough to leave the nucleus through pores in the nuclear envelope and enters the cytoplasm, where the coded information that it contains is used to determine the sequence of amino acids in the proteins which are synthesised there (in cytoplasm).
The mRNA and tRNA both use uracil instead of thymine.
mRNA is a long strand that is arranged in a single helix.
The base sequence of mRNA is determined by the sequence of bases on a DNA strand through a process called transcription.
It has codons (three bases in a triplet that make 1 amino acid).
What Is A Codon?
The sequence of three bases on mRNA that codes for a single amino acid.
What Is A Genome?
Genome is the complete set of jeans in a cell, including those in mitochondria and chloroplasts.
What Is A Proteome?
The full range of proteins produced by the gene on.
This is sometimes called the complete proteome, in which case the term proteome refers to the proteins produced by a given type of cell and a certain set of conditions.
What Is RNA?
Ribonucleic acid is a polymer made up of repeating mononucleotides sub-units.
It forms a single-strand in which each nucleotide is made up of:
- the pentose sugar, ribose,
- one of the organic bases; adenine, guanine, cytosine, and uracil,
- a phosphate group.
There are two types of RNA that are important in protein synthesis: mRNA and tRNA.
What Is tRNA?
Made up of around 80 nucleotides.
It is a single-stranded chain folded into a clover leaf shape, with one end of the chain extending beyond the other. This is the part of the tRNA molecule to which an amino acid can easily attached (amino acid binding site). There are many types of tRNA, each of which binds to a specific amino acid.
At the opposite end of the tRNA molecule is a sequence of three other organic bases, known as the anticodon. Given that the genetic code is degenerate, there must be as many tRNA molecules as there are coding triplets.
The mRNA and tRNA both use uracil instead of thymine.
tRNA is involved in translation. It carried the amino acids used to make proteins to ribosomes.
It is a single polynucleotide strand.
Hydrogen bonds between the specific base pairs hold the molecule together in its shapes
Basic Process (Overview) Of Protein Synthesis?
- DNA provides the instructions in the form of a long sequence of bases,
- Transcription,
- The pre-mENA is spliced,
- Translation.
Protein synthesis - transcription?
Transcription is the process of making pre-mRNA using part of the DNA as a template.
- An enzyme called RNA polymerase attaches on a region of DNA strands at the beginning of a gene. In eukaryotes, DNA helicase separates the hydrogen bonds between the two strands of DNA. This allows the DNA to uncoil. This exposes the nucleotide bases in that region. This region is called the transcription unit (a template).
- RNA polymerase lines up free nucleotides alongside the exposed bases on the template strand. The free bases are complementary and attached to template strand by phosphodiester bonds by RNA polymerase. This means the pre-mRNA ends up being complementary (except the T is resolved by a U in RNA, A-T for DNA. A-U for RNA).
- As the RNA polymerase adds the nucleotides one at a time to build the pre-mRNA, the DNA strand rejoins behind it. The hydrogen bonds are reformed behind and the DNA recoils into a double helix. As a result, only about 12 base pairs on the DNA exposed at any one time.
- When is the RNA polymerase reaches a ‘STOP’ triplet code, it detaches. The pre-mRNA is then compete and ready for the next step: splicing.
- In eukaryotes, the pre-mRNA moves out of the nucleus through a nuclear pore and attaches to the ribosome in the cytoplasm, where splicing takes place.
Transcription makes different products for eukaryotes and prokaryotes?
Eukaryotes- the introns and exons are both copied into mRNA during transcription. mRNA containing exons and intron is called pre-mRNA. Then splicing takes place to form mRNA. This takes place in the nucleus.
Prokaryotes - mRNA is produced directly from the DNA - without splicing having to take place. There is no need for splicing because there are no introns In prokaryotic DNA.
Protein synthesis - splicing?
DNA of a gene in eukaryotic cells is made up of nucleotide triplets called codons. These codons split into exons that code for proteins and sections called introns that do not code for anything.
These introns would prevent the synthesis of a polypeptide. Introns are removed by splicing. As most prokaryotic cells do not have introns, splicing of their DNA is unnecessary.
Splicing occurs in the nucleus.
Once splicing has occurred, the result is mRNA.
mRNA molecules are too large to diffuse out of the nucleus and so, once they have been spliced, diffuse out of nucleur pores.
Outside the nucleus, the mRNA is attracted to the ribosomes to which it becomes attached ready for the next stage of the process: translation.
Protein synthesis - tanslation?
There are about 60 different tRNAs.
Omce mRNA passes out of the nuclear pores, it determines the synthesis of a polypeptide.
Translation occurs in both prokaryotes and eukaryotes.
Translation occurs in ribosomes in the cytoplasm.
- A ribosome becomes attached to the starting codon (usually AUG) at one end of the mRNA molecule.
- The tRNA molecule with a complimentary anticodon would then move to the ribosome and binds with the codon on the mRNA. The tRNA carries a specific amino acid complimentary to its own anti-codon.
- A second tRNA molecule with a complimentary anticodon to the next codon on the mRNA pairs with the ribosome. This tRNA sits next to the first tRNA. The amino acid is left behind on the mRNA whilst the tRNA molecules move away.
- The ribosome moves along the mRNA, bringing together the two tRNA molecule one at a time, pairing them up with the corresponding to codons on the mRNA.
- The two amino acid’s on the tRNA are joined by peptide bonds using ATP and an enzyme. The ATP is hydrolysed to provide the required energy.
- The ribosome moves on to the third codon on in the sequence on the mRNA, thereby linking the amino acid is on the second and third tRNA molecules.
- The process continues in this way, with up to 15 amino acids being added each second, until the polypeptide chain is built up.
- Up to 50 ribosomes can pass immediately behind the first, so that many identical polypeptides can be assembled simultaneously.
- The synthesis of a polypeptide continues until the ribosome reaches a stop codon. At this point, the ribosome, mRNA and tRNA molecule all separate and the polypeptide chain is complete.
Polypeptide Structure?
The single polypeptide chain (amino acid sequence) is the primary structure.
The polypeptide is coiled or folded, producing a secondary structure. Alpha helies fold into beta sheets.
The secondary structure is folded, producing the tertiary structure. This is a 3-D fold.
Different polypeptide chains, along with any non-protein groups, are linked to form a quaternary structure. This is not for every protein.
Start And Stop Codons?
Start: AUG (in mRNA, not DNA),
Stop: UGA, UAA, UAG (in mRNA, not DNA).
