Nucuelic Acids And Protien Synthesis Flashcards
What do nucleotides consist of?
Five carbon sugar
And nitrogen containing organic base
An inorganic phosphate group
Characteristics of a nucleotide
Links through covalent bonding
Contain two different pentoses- ribose and deoxyribose
Four different bases occur in DNA and RNA- split into two groups:
Purines- adenine, guanine
Pyrimidines- cytosine, thymine and uracil
What is ATP (adenosine triphosphate)
A phosphorylated nucleotide, consisting of adenine and ribose, joined to 3 phosphate groups.
Adenine joined to ribose in this way forms adenosine
RNA (ribonuclease acid)
Single-stranded polynucleotide contain the bases adenine, cytosine, guanine and uracil
DNA (deoxyribonucleic acid)
Double-stranded polynucleotide that consists of two complimentary strands held together with hydrogen bonding (helix structure)
Bases are adenine, cytosine thymine, guanine
A+T
C+G
To polynucleotide strands are antiparallel because they run in opposite directions
How does DNA replicate?
Semiconservative replication- learn the experimental evidence
Semiconservative DNA replication
Two strands of DNA separate (H bonds break)
Each strand of DNA acts as a temp late for the synthesis of a new, complimentary strand alongside it
Complimentary bases to those in the DNA join together to form a complimentary strand of RNA
Semiconservative replication takes place during the S-phase of the cell cycle
The enzymes DNA helicase and DNA polymerase or involved in the process
What is the role of DNA helicase and DNA polymerase
DNA helicase-separate the two strands of DNA by breaking the hydrogen bonds between the base pairs
DNA polymerase- joins the nuclear tides together to form the new DNA
The genetic code
Genetic information- sequences of bases code for amino acids and amino acid’s code for polypeptides
Each part of the DNA molecule that codes for a particular polypeptide is a gene
Sequence of three bases- codon (64 possible codons)
Genetic code is said to be degenerate as it is possible for several different codons to specify the same amino acid
Two stages of protein synthesis
Transcription- in which a molecule of messenger RNA synthesised
Translation- The sequence of bases on the mRNA molecule is used to specify in the order in which amino acid’s are joined together to form a polypeptide
Process of protein synthesis
During transcription one strand is used as a template for the synthesis of a complimentary Strand of mRNA- done with the enzyme polymerase
mRNA leaves the nucleus and attaches to a ribosome in the cytoplasm- this is the site of protein synthesis (translated into appropriate chain of amino acids)
Protein synthesis involves transfer RNA- each molecule of tRNA has a region with three exposed bases (anticodon)
Anticodon and codon are complementary so the tRNA brings the correct amino acid to the ribosome
The ribosome moves along the mRNA, as it does, the tRNA molecules bring the correct amino acids as specified by the by the sequence of codons on mRNA
This creates a polypeptide chain and the process continues until a stop codon is reached
Mutation
A change in the nucleotide sequence in DNA- can result in a change in amino acid sequence in the polypeptide coded for by the affected gene
Sickle-cell anaemia
This mutation causes the formation of a type of haemoglobin known as haemoglobin S and results in sickle-cell anaemia
One of the codons for the beta chain of haemoglobin is altered from CTT to CAT
Results in the substitution of the amino acid valine to glutamic acid
