U2T3 - Keywords Flashcards
DNA as the genetic code
Purine bases
Larger, double ring structure. Adenine + guanine.
Pyrimidine bases
Smaller, single ring structure. Thymine (Uracil in RNA) + cytosine.
mRNA
Messenger RNA. Single chain twisted into helix, length + base sequence varies. Formed in nucleus by copying part of DNA (1 gene). Formed during transcription. Carries code for gene from nucleus to ribosomes in cytoplasm. Short life, involved in protein synthesis.
tRNA
Transfer RNA. Small molecule, single strand of RNA in clover leaf shape. 20 types, each carry diff AA. Anticodon at mid point, complementary to codon on mRNA. Requires ATP to attach to AA. Transport AAs within cytoplasm for protein synthesis + ensures each mRNA codes for particular AA, aligning codons + AAs.
rRNA
Ribosomal RNA. Large complex structure made in nucleolus. Forms over half mass of ribosomes.
Anticodon
Sequence of 3 bases in middle of tRNA, determines which AA attaches by lining up against appropriate codon on mRNA in protein synthesis. Brings AA’s to correct position on mRNA during translation.
Gene
Length of DNA which gives instructions for making 1 polypeptide.
Sense/Coding/Template Strand
Strand of DNA where code is stored in molecular structure. The strand which is copied by mRNA during transcription.
Triplet Code
20 diff AAs used to make proteins. Triplet code of 3 bases per AA produces 64 combinations 2 would give only 16). Each AA coded for by a codon.
Codon
Sequence of 3 DNA bases which code for an amino acid.
Degenerate Code
Multiple triplets of bases can code for same AA. First 2 bases are most important in determining which AA is coded for so mutation which substitutes 1 base for another may not alter the AA.
Non-Overlapping Code
Code read in discrete groups of 3 bases, no overlap in coding sequences.
Universal Code
DNA base triplets code for same AA in all organisms, allowing for development of gene technology so genes from one organism can be inserted into another species.
Gene Mutation
Involves change in sequence of DNA bases of gene + may lead to change in AA sequence of polypeptide. May alter the way protein functions + so disrupt metabolic pathways (CF)
Transcription
Copying DNA base sequence in mRNA in nucleus.
Translation
mRNA info translated into AA sequence in cytoplasm.
Intron
Non-coding DNA sequences. Some may regulate gene expression.
Ribosome
Small, free in cytoplasm/attached to ER. Contains large + small sub-unit, made of protein + rRNA. Has 2 binding sites for tRNA molecules. A (aminoacyl) + P (peptidyl) In translation, ‘A’ site binds aminoacyl-tRNA as directed by codon. ‘A’ site only works once first aminoacyl-tRNA has attached to P site. ‘P’ site codon occupied by peptidyl-tRNA which carries already synthesised AAs. ‘E’ site occupied by empty tRNA as about to exit ribosome
Peptidyl-tRNA
tRNA with multiple AA’s attached as long chain.
Epigenetics
Study of heritable modifications in the genome. Change in phenotype, rather than genotype as doesn’t change sequence, just extra bits added onto DNA. Can enhance or stop expression of gene.
CpG Island
CpG sequences grouped. If critical num islands methylated, DNA switched off + transcription can’t happen.
Genetic Code
The way DNA codes for specific amino acids in specific positions in a polypeptide.
Central Dogma of Molecular Biology
DNA replication cycle -> Transcription to RNA -> Translation to protein. However, retroviruses have reverse transcriptase to reverse transcription.
Epigenetic Modifications
Edits/extra bits added to genes which don’t change DNA sequence.