DNA, genes and protein synthesis Flashcards
DNA in eukaryotic cells
-Linear DNA molecules that exist as chromosomes
-DNA molecule is really long so it has to be wound up so it can fit into the nucleus
-DNA molec8le is wound around proteins called histones
-Histone proteins also help to support DNA
-DNA and protein is then coiled up tightly to make a compact chromosome.
-Mitochondria and chloroplast also contains DNA (similar to prokaryotic cells, short and circular and not associated with histones1a)
DNA in prokaryotic cells
-Shorter and circular
-Prokaryotes also carry DNA as chromosomes
-DNA isn’t wound around histones- condenses to fit in the cell by supercoiling.
What is a gene?
-A sequence of DNA bases that codes for either a polypeptide or functional RN.
-Sequence of amino acids in a polypeptide forms the primary structure of a protein.
-Different polypeptides have a different number and order of amino acids. Its the order of bases in a gene that determines the order of amino acids in a particular polypeptide
-Each amino acid is coded for by a sequence of three bases in a gene called triplet
-To make a polypeptide, DNA is first copied into messenger RNA (mRNA), first stage of protein synthesis
-Genes that don’t code for a polypeptide, code for functional RNA instead
-Functional RNA is RNA molecules other than mRNA, perform special tasks during protein synthesis e.g tRNA and ribosomal RNA which forms part of ribosomes.
What is a cell’s genome?
complete set of genes in the cell
What is a cell’s proteome?
full range of proteins that the cell is able to produce
What is an intron and why are they removed during protein synthesis?
A section of a gene that don’t code for amino acids.
they are removed so they don’t affect the amino acid order.
What are non coding repeats?
The sequence that repeat and dont code for amino acids
What is an exon
A sequence of a gene that codes for amino acids
What is a locus?
fixed position
what are alleles?
genes can exist more than one form
-order of bases in each allele is slightly different so they code for slightly different versions of the same polypeptide such as the gene that determines the blood type.
Describe how mRNA is formed by transcription in eukaryotes.
1)Hydrogen bonds between the two DNA strands in the gene are broken by a DNA helicase, separating the strands
2)DNA molecule uncoils, exposing the bases
3)One of the strands is then acts as a template to make an mRNA copy
4)Free RNA nucleotides align by complementary base pairing to the exposed bases on template
5)Uracil base pairs with adenine and it is used in place of thymine
6)RNA polymerase joins adjacent RNA nucleotides by phosphodiester bonds between the adjacent nucleotides.
7)This forms pre-mRNA which is then spliced to form mRNA. This is done by a protein called splicesome which splice out introns from the pre-mRNA.
8)mRNA then leaves the nucleus for translation
Describe how a polypeptide is formed by translation of mRNA
1)mRNA attaches to a ribosome in the cytoplasm
2)tRNA anticodons bind to complementary mRNA codons by complementary base pairing.
3)Each tRNA carries a specific amino acid
4)Amino acids join together by peptide bonds with the use of ATP
5)tRNA released after amino acid join together to polypeptide
6)Ribosome moves along the mRNA to form the polypeptide until the stop signal on the mRNA molecule.
7)Polypeptide chain moves away from the ribosome and translation is complete.
What is mRNA
-Made during transcription
-Carries the genetic code from the DNA to the ribosomes where it is used to make a protein during translation
-Single polynucleotide strand
-Groups of three adjacent bases called codons
What is tRNA and the structure
-Carries amino acids that are used to make proteins to the ribosomes
-Single polynucleotide strand thats folded into a clover shape.
-Hydrogen bonds between specific base pairs hold the molecule in this shape.
-Every tRNA has a specific sequence of three bases at one end called an anticodon and have an amino acid binding side at the other end
