3.4.1 DNA, genes and chromosomes Flashcards
What are the four bases found in DNA?
Adenine, Thymine, Cytosine, Guanine
What is the meaning of a triplet code?
Three bases ( A Codon) codes for an amino acid
What is the meaning of non-overlapping code?
Each amino acid is independent - codons read one after the other
What is the meaning of degenerate code?
Multiple codon codes for the same amino acid
What is the meaning of universal code?
ATCG are used to code for DNA in all species
What are homologous chromosomes
A pair of chromosomes that are equal in length, have same position of centromere + same genes (sometimes different alleles caused by mutation)
What are histone proteins?
DNA wrap around histone proteins which curls up and condenses to form chromosomes
Why are histone proteins not found in prokaryotes?
DNA are in form of circular / loops in prokaryotes
What are exons?
Genes - section of DNA that codes for a protein / functional RNA
What is the locus?
Position of a gene in a chromosome
What could be a consequence of mutation
Result in stop codon - non-functional DNA - stop remaining codon from being made
What are introns?
Non-coding DNA - gaps between genes
What is the genome of a cell?
The complete set of genes in a cell
What is the proteome of a cell?
The full name of proteins a cell is able to produce
What is transcription?
Where DNA is copied into a molecule of mRNA
What is translation?
Where mRNA joins with ribosomes and the sequence of bases is used to synthesise a protein
What is protein synthesis?
Production of from a cell’s genes
What happens in the process of transcription?
- RNA Polymerase (enzyme) attaches to DNA double helix, unzips it (hydrogen bonds between bases broken with DNA helices attached to the RNA polymerase)
- Complementary pre-mRNA is formed as free bases attach to exposed complementary bases. RNA Polymerase then catalyses the formation of phosodiester bonds in newly formed pre-mRNA
- RNA Polymerase moves down the DNA strand and assembles pre-mRNA strand. Hydrogen bonds reform between uncoiled strands of DNA and coils back into double helix
- RNA Polymerase reaches stop codon. Production of mRNA ends and RNA polymerase detaches from the DNA
- Pre-mRNA will be spliced into mRNA. Introns are removed by forming a spliceosome and be cut off, the exons join together. mRNA then move out of the nucleus though nuclear pores into the cytoplasm
What happens in the process of translation?
- mRNA attaches itself to a ribosome and amino acids are activated - combined with tRNA
- ATP is hydrolysed in the process of joining amino acid with tRNA
- tRNA molecule has an anticodon that’s complementary to codon on mRNA
- tRNA with the start codon will attach to the mRNA and start the process of translation, mRNA is located in between subunits of ribosomes
- Ribosome moves along mRNA, one codon at a time, more tRNA attach on mRNA
- Peptide bonds are formed between amino acids brought by tRNA, catalysed by enzymes found in ribosomes
- As ribosomes move along, tRNA that are no longer between ribosomes are released back into the rest of the cytoplasm and will activate more amino acids
- Process of translation continues until there’s a stop signal
- Polypeptide chain then moves away from the ribosome as translation is complete
- mRNA strand could be translated by thousands of ribosomes, producing a lot of proteins
What is the structure and function of mRNA?
Made during transcription
Carries genetic code from DNA to ribosome for protein synthesis
A single polypeptide strand
Chain of codons
What is the structure and function of tRNA?
Carries amino acids to mRNA during translation
A single polypeptide chain that is folded into clover shape
Amino acids binding site at the top
Anti-codon loop at the bottom
