3. Enzymes & Protein Synthesis Flashcards
What is the lock and key theory?
A substrate is complementary to the enzyme’s active site.
The substrates form temporary bonds with the amino acids in the active site to form an enzyme-substrate complex.
After the reaction has been carried out the products are released and the enzyme is unchanged
What is the induced-fit theory?
The enzyme’s active site will change to slightly to fit more closely around the substrate. Only specific substrate’s will induce this change in shape however
How do enzymes lower the activation energy?
Charged sites on the substrate and active site interact and the oppositely charged groups distort the substrate to assist in bond making or bond breaking.
Why is it important for the activation energy to be lowered?
The normal energy required for the reaction to start would damage the cell and it also speeds up the rate at which reactions happen.
What happens in a catabolic reaction?
Larger substrates are broken down
What happens in an anabolic reaction?
Product is built up
What is the effect of enzyme concentration on the rate of a reaction assuming substrate is always in excess?
The initial rate will be directly proportional to the enzyme concentration as there are a greater number of active sites to form enzyme substrate complexes.
What effect does substrate concentration have on the rate of reaction?
Initially substrate conc. produces more successful enzyme-substrate collisions so rate increases.
As the conc continues to be increased the enzymes become a limiting factor as all active sites are full so there is no overall effect on the rate
What is the structure of a DNA nucleotide?
phosphate group, deoxyribose sugar and an organic base e.g A, T, C, G
What type of bond holds adjacent nucleotides together?
phosphodiester
How many hydrogen bonds does the AT pairing form?
2
How many hydrogen bonds does the CG pairing form?
3
What type of reaction joins mononucleotides together to form a polynucleotide?
condensation reaction
What term is used to describe the pairs of bases?
complementary
Where does transcription take place?
Nucleus
Describe the process of transcription.
- Hydrogen bonds break and the double helix unwinds
- Free RNA nucleotides line up against their complementary base on the template strand
- Once a stop code is reached the mRNA molecule detaches from the DNA and leaves the nucleus into the cytoplasm
What is the structure of an RNA nucleotide?
Phosphate group, ribose sugar, organic base e.g. A, U, C, G
Which organic base is replaced by uracil in RNA?
Thymine
Which enzyme is involved in transcription?
RNA polymerase
Describe the process of translation.
- mRNA molecule binds to a ribosome where the process takes palce
- tRNA molecule carrying an amino acid binding site pairs with the codon on the mRNA that is complementary to its anticodon
- The amino acids are brought close together so join in condensation reactions to form peptide bonds
What are two differences between an mRNA and a tRNA molecule?
- tRNA has an amino acid binding site and mRNA does not
2. mRNA is a single strand where as tRNA is folded and held in place by hydrogen bonds
