DNA

What is Transcription? What is Translation? What is a gene ?

- The process of making messenger RNA from a DNA template -Formation of a protein at the ribosomes by assembling amino acids into a particular sequence according to the coded instructions carried from DNA to the ribosomes by mRNA A length of DNA that codes for a polypeptide or for a length of RNA that is involved in regulating gene expression

DNA replication - Steps

-Replication starts at a specific sequence on the DNA molecule. -An enzyme unwinds using a gyrase enzyme and unzips DNA, using DNA helicase enzyme breaking the hydrogen bonds that join the base pairs, and forming two separate strands. -Free nucleotides are hydrogen bonded onto the exposed bases according to the base pairing rules using DNA polymerase - Covalent bonds (phosphodiester bonds) are formed between the phosphate of one nucleotide and the sugar of the next to seal the backbone . Hydrogen bonds form between base pairs. - On the leading strand DNA is built in the 5' to 3' direction continuously - On the lagging strand DNA is built in fragments in the 3' to 5' direction

Transcription

- The DNA unzips and unwinds -The hydrogen bonds are broken - The enzyme RNA polymerase catalyses the formation of temporary hydrogen bonds between RNA nucleotides and their complementary unpaired DNA bases. -A length of RNA that is complementary to the template strand of the gene is produced. It is therefore a copy of the other DNA strand - the coding strand -The mRNA diffuses out of the nucleus through a nuclear pore into the cytoplasm.

What is mRNA?

Messenger RNA (mRNA) mRNA carries the "message" that codes for a particular protein from the nucleus (where DNA is) to the cytoplasm (where proteins are synthesised). It is single stranded and just long enough to contain one gene only.

The nature of the genetic code

Mutations happen during replication - The genetic code is near universal because almost all living organisms have the same triplet code of DNA bases for the same amino acid - The genetic code is degenerate because for every amino acid except two there is more than one base triplet that will code for this amino acid -This may reduce the effect of point mutation as a change in one base of the triplet code can still code for the same amino acid -The genetic code is non overlapping. It is read from a fixed point in group in groups of 3 . If a base is added/ deleted then it causes a frame shift mutation as every base triplet after that is affected therefore every amino acid coded will be changed.

What are the components of nucleotides?

Nucleotides - A molecule consisting of ... Nucleotides have three parts to them: -A phosphate group, which is negatively charged. - A pentose sugar, which has 5 carbon atoms in it. In RNA the sugar is ribose. In DNA the sugar is deoxyribose. -A nitrogenous base. There are five different bases (you don't need to know their structures). The bases are usually known by there first letters only, you don't need to learn the full names. The base thymine is found in DNA only and the base uracil is found in RNA only. The Bases: Adenine (A), Thymine (T), Cytosine (C), Guanine (G) and Uracil (U)-- A and G are double ring structures

What do nucleotides do?

Nucleotides become phosphorylated nucleotides when they contain more than one phosphate group e.g ADP ( adenosine diphosphate) and ATP ( adenosine triphosphate). ATP is an energy rich product of most energy biochemical pathways and is used to drive energy requiring metabolic pathways. They also help regulate metabolic pathways .

Nucleotide polymerisation

Nucleotides polymerise by forming bonds between the carbon of the sugar and an oxygen atom of the phosphate. The bases do not take part in the polymerisation, so the chain is held together by a sugar-phosphate backbone with the bases extending off it. This means that the nucleotides can join together in any order along the chain. Many nucleotides form a polynucleotide. A polynucleotide has a free phosphate group at one end and a free OH group at the other end.

What is RNA?

RNA RNA is a nucleic acid like DNA, but with 4 differences: RNA has the sugar ribose instead of deoxyribose RNA has the base uracil instead of thymine RNA is usually single stranded RNA is usually shorter than DNA

What are purines and pyrimidines ?

DNA consists of just 4 types of DNA . In each nucleotide the phosphate and sugar groups are the same but the organic nitrogenous bases are different. It may either be A purine(adenine or guanine) --> 2 rings A pyrimidines( Thymine or cytosine) --> 1 ring A&T makes 2 bonds G&C makes 3 bonds Click to zoom

What is a base triplet? What is a codon? What is a anti codon?

A triplet of bases on a DNA molecules is called a base triplet A triplet of bases on length of mRNA is called a codon A triplet of bases on a tRNA molecule complementary to the mRNA codon is called an anti codon

Function of DNA

DNA is the genetic material, and genes are made of DNA. DNA therefore has two essential functions: replication and expression. Replication means that the DNA, with all its genes, must be copied every time a cell divides. Expression means that the genes on DNA must control characteristics. A gene is a section of DNA that codes for a particular protein. Characteristics are controlled by genes through the proteins they code for, like this: Expression can be split into two parts: transcription (making RNA) and translation (making proteins).

What is DNA polymerase? What is DNA helicase? What is semi conservative replication?] What is dispersive replication?

DNA polymerase - the enzyme that catalyses the formation of DNA from activated deoxyribose nucleotides using single stranded DNA as a template. Helicase - enzyme that catalyses the breaking of hydrogen bonds between nitrogenous pairs of bases in DNA Semi conservative replication- how DNA replicates resulting in 2 new molecules each of which contains 1 old strand and 1 new strand

What is DNA What is a polynucleotide? What is a double helix ?

DNA stands for deoxyribonucleic acid and RNA for ribonucleic acid. They are polymers (long chain molecules) made from nucleotides. Large molecule containing many nucleotides Shape of DNA molecule due to coiling of the two sugar phosphate backbone strands into a right handed spiral configuration. .

Translation

Ribosome catalyses the synthesis of polypeptide - Transfer RNA molecules bring the amino acids and find their place when the anti-codon binds by temporary hydrogen bonds to the complementary codon on the mRNA molecule. - As the ribosome moves along the length of mRNA it reads the code and when two amino acids are adjacent to each other a peptide bond forms between them. -Energy in the form of ATP is needed for polypeptide synthesis - The amino acid sequence for the polypeptide is determined by the sequence of triplets of nucleotide bases on the length of DNA -After the polypeptide has been assembled the mRNA break down and the component molecules can be recycled into new lengths of mRNA.

What is the structure of DNA?

Structure of DNA: The main features of the three-dimensional structure of DNA are: DNA is double-stranded, so there are two polynucleotide stands alongside each other. The two strands are wound round each other to form a double helix. The two strands are joined together by hydrogen bonds between the bases. The bases therefore form base pairs, which are like rungs of a ladder. The base pairs are specific. A only binds to T (and T with A), and C only binds to G (and G with C). These are called complementary base pairs. This means that whatever the sequence of bases along one strand, the sequence of bases on the other strand must be complementary to it.

What is an anti parallel sugar phosphate backbone

The opposite strands of the direction of the two strands refers to the directions that the third and fifth carbon molecules are facing in on the 5 carbon deoxyribose suagr. The 5'end of the molecule is where the phosphate group is attached to the fifth carbon of the deoxyribose sugar. The 3'end is where the phosphate group is attached to 3rd carbon atom of the deoxyribose sugar. the rungs of the ladder are the complementary base pairs joined by hydrogen bonds.

What is tRNA

Transfer RNA (tRNA) tRNA matches amino acids to their codon. tRNA is only about 80 nucleotides long, and it folds up by complementary base pairing to form a clover-leaf structure. At one end of the molecule there is an amino acid binding site. On the middle loop there is a triplet nucleotide sequence called the anticodon. There are 64 different tRNA molecules, each with a different anticodon sequence complementary to the 64 different codons on mRNA.

How do polynucleotides form from nucleotides ? How is a nucleotide similar to the structure of ATP?

Two nucleotides join a condensation reaction. This creates a phosphodiester bond between the OH group on the phosphate group of the nucleotide. Similarities: - Same base, Pentose sugar, Contains at least on phosphate . Differences: - 3 phosphate gorups whereas DNA contains one phosphate group , Ribose sugar used in ATP whereas Deoxyribose sugar used in DNA