Definition of DNA and structure
Deoxyribosenucleic acid, the materal of which genes are made. A double helix, consisting of sugar-pospate back bone with proturding bases that link to bases on the other strand. DNA is stored in the nucleus of every cell and is cotained in chromosomes.
The enzyme that transcribes oneof the two DNA strands to form a complementary strand of RNA
Ribonucleic Acid. A single stranded molecule similar to DNA, but with a base Uracil instead of Thymine and the sugar is ribose isnstead of deoxyribose. Transfers genetic information from the DNA to Cytoplasm for Protein Synthesis.
Messenger RNA. Single stranded RNA complementary in base sequence to DNA. Carries genetic infomation
from DNA to ribosome. Its base sequence determines the sequence of a polypeptide chain.
Small organelle in the cytoplasm that is the site of protein synthesis. Made up of rRNA and protein tRNA.
Transfer RNA. Short RNA molecules that bind with specific amino acids and bring them to complementary RNA codons to form a polypeptide chain at the ribosome.
The production of a complementary mRNA strand from the template DNA strand.
Process of Transcription ( _ Steps)
- 1. In the nucleus, DNA is unwound by RNA polymerase enzyme exposing two strands of DNA.
- 2. One strand (template DNA) acts as a template for mRNA to be made complementary to.
- 3. mRNA is synthesised by RNA polymeraseL it is made complementary to template DNA strand according to the following base pair rules: A to U and C to G.
- 4. A particular sequence of DNA bases/triplet signals the START of the the protein AUG. While other sequences signal the end/STOP of protein VAG, VGA.
- 5. Once the complete sequence is copied the mRNA molecule detaches and moves out the nucleus into the cytoplasm.
mRNA leaves the nucleus through this opening.
The formation of protein (or polypeptide chain) starting with a mRNA strands which code fo specific amino acids.
Section of DNA not translated/not coding for an amino acid. It is removed after transcription.
A segement of DNA coding for a specific amino acid.
Processing ( _ steps)
- 1. After transcription the introns are spliced out by a splicesosome.
- 2. The exons are 'glued' together by ligase.
- 3. 'Mature' mRNA then goes to the ribosome where translation occurs.
Three consecutive bases of mRNA that code for a specifc amino acid.
Group of three bases of a tRNA which is complementary to and therefore can combine to, the codon of a mRNA.
Molecules which join together to form proteins- there are 30 different amino acids which are used to make protein.
A chain of amino acids linked togehter by peptide bonds. One or several polypeptide chains form a protein.
The link between amino acids in a protein.
Translation Process (7 Steps)
- 1. The mRNA attachers to a slot at the ribosome.
- 2. The ribosome moves along the mRNA moecule reading the base sequences/codons
- 3. As each codon is read a tRNA with a complementary base sequence on its anticodon attaches to the codon.
- 4. Each tRNA carries a specific amino acid.
- 5. Adjacent amino acids added by tRNAs are joined together by peptide bonds forming a polypeptide chain.
- 6. tRNA molecule is then released to pick up another amino acid.
- 7. When the ribosome reaches a particular mRNA sequence/STOP codon, the tranlsation stops and the polypeptide chain is released.
The fact that most of the amino acids are coded for by a number of different codons.
The process of making two exact copies of the original DNA.
Why does DNA need to replicate itself?
When a cell divides for growth and repair, each new cell must have a full set of genes in order to function correctly. Genes are made of DNA so it is necessary to replicate DNA before the cell divides.
DNA replication where each 'daughter' molecule consists of half new, half old material.
Enzyme tha unwinds the DNA double helix during DNA replication.
The point where the DNA is split into two strands in replication
The enzyme that joins new nucleotides (following base-pair rules) to the template DNA strand during replication. Nucleotides are added in the 5' to 3' direction.
The strand of DNA formed with few/no interruptions during replication. It is synthesised in the direction toward the replicationn fork 5'to3'
The strand of DNA formed by joined Okazaki fragments during DNA replication. Synthese in the direction away from the replication fork (5'to3')
The enzyme the joins Okazaki fragments together during replication.
DNA replication steps
- DNA Helicase unwinds DNA
- DNA polymerase adds nucleotides following base pair rules in the 5'to 3' direction. In the leading strand this is uninterrupted. In the lagging strand this is done in shorter fragments called okazaki fragments which is joined by DNA ligase.
- The product of DNA replication are two exact copies of the target DNA.
DNA is not contained in a nucleus
In bacteria, the group of genes controlled by the same switch
Gene which makes a protein that controls the rate and which the product of another gene is made. e.g. produces repressor molecule.
The specific DNA sequence where RNA polymerase attaches, indicates where to start transcribing.
The sequence of DNA before the gene-coding sequences to whichi a repressor attaches to switch the operater off.
The molecule that binds to the operator site and blocks RNA polymerase and prevents transcription. It is produced by the regulator gene.
- Molecule that turns genes 'on'.
- Changes the repressor shape
- e.e lactose in lac operon.
Two structural genes made by lac operon
- Beta galactosidase
- Lactose permease