Nucleic Acids And Protein Synthesis Flashcards
Nucleotides & polynucleotides
Molecule consisting of a nitrogen containing base, a pentose sugar and a phosphate group
A chain of nucleotides joined together by phosphodiester bonds
Phosphodiester bond
Bond joining two nucleotides together, 2 ester bonds, one from the shared phosphate group to each of the sugars either side of it
Visual : -o-
Complementary base pairing
Hydrogen bonding of A with T (or U in RNA) and of G with C in nucleic acids
AT have double H- bonds GC have triple
Purines & Pyrimidines
Purines are two rings wide, A and G are purines
Pyrimidines are one ring wide, T,U and C are Pyrimidines
Purines and Pyrimidines always pair together so backbone of DNA is always 3 rings wide
DNA Polymerase
Enzyme that copies DNA, runs along the separated DNA strands lining up one complementary nucleotide at a time ready to be joined by DNA Ligase
DNA Ligase
Enzyme that catalyses the joining together of two nucleotides with covalent phosphodiester bonds during DNA replication
Leading strand & Lagging strand
During DNA replication, the parent strand that runs in the 3’ to 5’ direction is copied to produce the leading strand.
The parent strand that runs in the 5’ to 3’ direction copied to produce lagging strand, coping opposite to direction of unwinding so it needs to keep jumping backwards resulting in short fragment called Okazaki fragments
Semi-conservative replication
Method by which DNA molecule is copied to make 2 identical molecules each containing one strand from original molecule and one newly synthesized strand
Gene
Length of DNA coding for a particular polypeptide or protein
Transcription
Copying the genetic information in a molecule of DNA into a complementary strand of mRNA.
A single strand of the DNA is used as a template (called template/ transcribed strand ).
Enzyme responsible: RNA polymerase
Translation
Stage in protein synthesis where a sequence or nucleotides in a molecule of mRNA is converted (or translated) into a corresponding sequence of amino acids in a polypeptide chain.
It takes place in ribosomes
Codon
Sequence of three bases on a mRNA molecule that codes for a specific amino acid /for a stop signal
Anticodon
Sequence of three unpaired bases on a tRNA molecule that binds with codon on mRNA
Gene mutation
Change in base sequence in part of a DNA molecule
Chromosome mutation
A random and unpredictable change in the structure or number of chromosomes in a cell
Frame shift mutation
A type of gene mutation caused by insertion of deletion of one or more nucleotides, resulting in incorrect reading of genetic code due to shift in the reading frame.
DNA/RNA general structure
- macromolecules known as nucleic acids
– monomers are nucleotides
-DNA/RNA are polynucleotides
- Nitrogen containing bases: Adenine, Thymine, Cytosine. In RNA T is replaced by Uracil.
- Pentose sugar: only 2 types: Ribose & Deoxyribose
3.Phosphate group : gives nucleic acids in their acidic nature.
DNA structure
- 2 polynucleotide chains, coiled —–> double helix
-chains run opposite directions, called antiparallel - sugar phosphate backbone
-bases bonded by H -bonding and holds chains tgt
-complete turn every 10 base pairs
Modification
-Called mRNA processing
-before leaving the nucleus the mRNA is slightly changed
- before modification is called the primary transcript
Protein synthesis
-has 2 stages
1. Transcription: writing of the information of the gene in the nucleus- and mRNA copy is made
2.Translation : at ribosome mRNA is used to form a polypeptide
Th triplet code
-3 bases on the DNA code for one amino acid
-the sequence is always read in one direction on one strand of DNA
-is degenerate meaning that each amino acid is coded for by more than one triplet (bc there is more than necessary only have 20 amino acids but 64 combinations)
Transcription
-mRNA is built up by complementary base pairing using the DNA as a template (u instead of t)
-DNA’s triplets are converted into mRNA CODONS
Steps:
- Helicase unwinds the DNA
2.RNA polymerase binds to the DNA at the beginning of the gene to be copied - single stranded RNA copy of the template stand is made stopping when it reaches the terminator sequence.
4.last 3 nucleotides on mRNA code for STOP - H bonds holding DNA and mRNA break and release mRNA
