4A - DNA, RNA, Protein Synthesis Flashcards
(12 cards)
how is nuclear eukaryotic DNA stored?
although DNA structure is same for all organisms, eukaryotic and prokaryotic cells store it differently.
- eukaryotic cells store DNA as linear molecules, which exist as chromosomes
> thread like strucs each
consist of one long DNA
molecule
- - DNA molecules are long so are wound so fits in nucleus
- theyre wound round proteins called histones; also support
- DNA (and protein) is coiled very tightly
= compact chromosome
the mitochondria and chloroplasts have own DNA
> similar to prokaryotic DNA as circular and shorter than
nuclear DNA molecules (also not associated with histones)
hows DNA stored in prokaryotes
they also carry DNA as chromosomes , but molecules are shorter and circular
-> DNA isnt coiled round histones
- it condenses to fit in cell by supercoiling (becomes coiled, then bunches up too)
what are genes in DNA
- the a.a. sequence in polypeptides form the primary struc of a protein
- diff polypeptides have diff number and order of a.a.s
» its order of bases in a gene that determines a.a. order in a polypeptide
>
»each aa is coded for by a sequence of three bases in a gene (triplet)
..
to make polypeptides, DNA is copied into mRNA in protein synthesis
- genes that dont code for a polypeptide
- code for functional RNA
–> RNA molecules other than mRNA ; perform special tasks in protein synthesis like tRNA, ribosomal RNA (form ribosome parts)
whats a genome and proteome
genome is the complete set of genes in the cell
proteome is the full range of proteins a cell’s able to produce
what happens to the DNA in eukaryotic cells that dont code for polypeptides ,in protein synthesis
genes that do code for polypeptides contain sections that dont code for aas
- these DNA sections are introns ; there can be several in a gene
- the parts of a gene that do code for aas are exons
-
- introns are removed in protein synthesis so dont affect amino acid order
- prokaryotic DNA = no introns
..
eukaryotic DNA also contain regions of multiple repeats outisde genes
» DNA sequences that repeat over and over (CCTTCCTTCCTT)
» these areas dont code for aas either, so called non-coding repeats
what are alleles
genes exist in diff forms called alleles
- the order of bases in each allele is slightly diff,
coding for slight diff versions of same polypeptide
– eg. a gene determining blood type exists as 1 of 3 alleles (O,A,B)
whats a homologous pair of chromosomes? and a locus?
humans have 23 pairs of chromosomes = 46 total
- two number 1s, etc
the pairs of matching chromosomes (eg 1s) are homologous pairs
in a homologous pair, both chromosomes are
- same size and have same genes
- but may have diff alleles
» alleles coding for same characteristic will be found at same fixed position (locus)
on each chromosome in a homologous pair
whats the difference between t and m RNA
RNA is a single polynucleotide strand and it contains uracil (U) as a base instead of thymine
- U always pairs with adenine in protein synthesis
messenger RNA (mRNA) - made during transcription - carries genetic code from DNA to the ribosomes - where its used to protein in translation - - mRNA is a single polynucleotide strand - in mRNA groups of 3 adjacent bases are called codons/triplets
..
transfer RNA (tRNA)
- invloved in translation; carries aas used to make proteins to ribosomes
-
- is a single polynucleotide strand , folded into clover shape
- H bonds between specific base pairs hold the molecule in this shape
»all tRNA have a specfic sequence of 3 bases at one end (anticodon)
» have an aa binding site at other end
DNA triplet, mRNA codon
whats the first protein synthesis stage - transcription
in transcription, an mRNA copy of a gene is made from DNA
» in eukaryotic cells, transcription takes place in nucleus; prokaryotes=cytoplasm
- transcription starts when RNA polymerase attaches to DNA double-helix at beginning of a gene
- in eukaryotes the H bonds between the two DNA strands ina gene
- are broken by DNA helicase attached to DNA polymerase
- separating strands and DNA uncoils , exposing some bases - one of strands is a template to make an mRNA copy.
- lines up free RNA nucleotides alongside exposed babes on template strand - the free bases are attracted to exposed bases
- specific complimentary base pairing means mRNA strand ends up
- being a complimentary copy of DNA template strand (U replaces T) - once RNA nucleotides have paired with specific bases on DNA , theyre joined by RNA polymerase (forming mRNA molecule)
- RNA polymerase moves along DNA , separating the strands and assembling mRNA strand
- the H bonds between uncoiled strands of DNA reform once RNA polymerase has passed by
- strands coil back into double helix - when RNA polymerase reaches a particular DNA sequence called stop signal
- it stops making mRNA and detaches
- then moves out nucleus through nuclear pore and attaches to ribosome in cytoplasm
what are the transcription products in eukaryotes and prokaryotes
eukaryotes
- introns and exons are both copied into mRNA
- mRNA containing both of these are pre mRNA
- introns are then removed and exons join ; in nucleus (splicing) forming mRNA strands
- then leaves nucleus
prokaryotes
- mRNA is produced directly from DNA without splicing (no introns)
what’s translation
in ribosomes.
aas are joined together to form a polypeptide chain, following the sequence of codons from mRNA
- mRNA attaches to ribosome; tRNA carries aas to it
- atp provides the energy for bond between aa and mRNA to form - tRNA with an anticodon complimentary to first codon on mRNA
- attaches itself to mRNA by specific base pairing
- second tRNA attaches to next codon in same way - two aas attached to tRNA molecules are joined by peptide bond
- first tRNA moves away , leaving aa - a third tRNA binds to next codon on mRNA; its aa binds to the first two and second tRNA goes away
process continues producing a polypeptide chain (chain of linked aa) until stop signal on mRNA
- polypeptide moves away from ribosome
how is genetic code non overlapping, degenerate and universal
genetic code is a code in your genes that tells your body how to make proteins
» sequence of base triplets (codons) in mRNa wch code for specific aas.
- in genetic code, each codon is read in sequence , separate from triplet before and after it
codons dont share their bases; code is NON OVERLAPPING - genetic code is degenerate; more possible combos of codons (64) than aas (20)
- so some aas are coded for by more than one codon
-
- some triplets tell cells when to stop and start protein production
- (start and stop signals/codons) theyre found at start and end of mRNA - is also universal; same specific codons code for same aas in all living things
