B1.2 What happens in cells? Flashcards
DNA
There is DNA in the nucleus of every one of your cells. Almost everyone’s DNA is unique, the only organisms that share identical DNA are identical twins and clones.
Chromosome
Every long molecule of DNA is a chromosome. Most people have 46 chromosomes in each one of their cells. However other organisms are different forexample chickens have 78 chromosomes. You inherit half your chromosomes from your mother and the other half from your father.
Gene
DNA is split up into sections. A gene is a section of DNA that codes for a characteristic, for example eye colour. The code that a gene contains causes specific proteins to be made. The particular protein made controls the cell’s function.
DNA appearance
DNA is made up of two strands which are joined together by bases. These strands are then twisted forming a shape known as a double helix
Nuclotides
DNA is made up of of small units called nucleotides, which are joined together, which means DNA is a polymer. Each nucleotide is made up of a phosphate, deoxyribose sugar, and a base.
Bases
There are four different types of nucleotides in DNA and each has a different base. The four bases are: adenine (A), thymine (T), cytosine (C), and guanine (G). To hold these two DNA strands together the bases need to form base pairings. The base pairings are always in the same formation as they are complementary to each other:
Adenine always bonds with thymine (A-T)
Cytosine always bonds with guanine (C-G)
Transcription
DNA is too big to move out of the nucleus so a copy of DNA called mRNA is made through the process transcription. The DNA around a gene unzips so that both strands are separated. One DNA strand acts as a template. Complementary bases attach to the strand being copied, for example cytosine joins to guanine. There is no thymine in mRNA so a base called urisil binds to adenine. This forms a strand of mRNA. Once completed, the mRNA strand detaches itself from the DNA template and the DNA zips back up.
Translation
The mRNA strand now can exit the nucleus and travels to sub cellular structures in the cytoplasm called ribosomes. This is where protein will be made in the process of translation. The mRNA attaches to a ribosome. Here the nucleotide sequence is interpreted and the new protein is made. The ribosome reads the mRNA in group of three called condons. Each condon codes for a specific amino acid. The ribosome then continues to read the mRNA in groups of three, adding more and more amino acids creating a long chain. This is a protein.
Why is the sequence of amino acids important?
The sequence of amino acids is important for protein function as it determines how the protein folds as each protein has a specific shape.
Enzymes
Enzymes are biological catalysts - which means that they are able to speed up a reaction without being used up of themselves. Once a reaction has finished they can be used to catalyse the same type of reaction again. Enzymes are involved in many reactions in your body: they can build up larger molecules from smaller ones (for example in protein synthesis) and can break down larger molecules into smaller ones (in digestion)
Why are enzymes highly specific?
Enzymes are highly specific as they can only bind to one type of substrate. The substrate must fit exactly in the enzyme or else it won’t bind. When the substate binds to the enzyme an enzyme substrate complex is formed. The reactions then happen quickly and the product is released from the enzyme and is then ready to catalyse another reaction.
Active site
The active site is an important part of the enzyme where molecules bind to the enzyme.
Substrate
The molecule that binds to the enzyme
