DNA and protein synthesis Flashcards
describe the structure of DNA
-building blocks are nucleotides (phosphate, 5-carbon sugar, and nitrogen base)
-4 types of nitrogen bases: adenine, thymine, cytosine, and guanine
-double helix
-deoxyribose sugar and phosphates are bonded together to make up the sides
-strands run antiparallel
-5’ end = an attached free phosphate
-3’ end = an attached -OH group
which base matches with which? what percentage do they make up in human cells?
-a and t (31%)
-c and g (19%)
what happens in DNA replication?
-two DNA strands held together by hydrogen bonds are separated
-each old strand (side) acts as a template for teh new strand (semiconservative)
-DNA helicase unwinds DNA
-new nucleotides are complementary base-paired
-addition of new strand is completed by DNA polymerase (synthesizes in 5’ –> 3’ direction)
-any gaps/breaks are fixed by DNA ligase
-at each origin of replication a fork forms, and a buble forms around it (where replication occurs)
how are DNA and RNA’s structures similar?
-both nucleic acids
-both made of nucleotides
-both have a sugar-phosphate backbone
-both have 4 base types
how are DNA and RNA’s structures different?
-DNA is a double helix that’s strands run antiparallel, made of deoxyribose sugar, has bases of ATCG
-RNA is a single stand, made of ribose sugar, and has bases of AUCG
mRNA function
-made in nucleus where DNA serves as a template for mRNA during transcription
-carries genetic info from DNA (nucleus) to ribosomes (cytoplasm) for translation and protein synthesis
tRNA function
-produced in nucleus
-transfers amino acids present in cytoplasm to ribosomes
-each of the 20 amino acids has its own tRNA moleucle
-at the ribosome translation joins amino acid brought by tRNA to form polypeptide chain
rRNA function
-produced in nucleolus where portion of DNA serves as template for formation
-joins with proteins made in the cytoplasm to form ribosome subunits
-subunits leave nuclues and come together in cytoplasm where protein syntehsis will happen
-each subunit is a unique mix of proteins and rRNA
-ribosomes can exist in cytoplas as clusters or free standing, often attached to ER
what are the two parts of protein synthesis?
-transcription: portion of DNA serves as mRNA template
-translation: sequence of mRNA bases determines sequence of amino acids folded together to create protein
describe transcriptoin
mRNA is formed by:
-RNA polymerase binding to a promoter
-opening up DNA helix just in front of it
-complementary base pairing RNA nucleotides
mRNA is then processed in the nucleus by:
-adding a cap of altered guanine nucleotide
-adding a poly-A tail to the 3’ end
-splicing the extrons together after removing the introns
what is a promoter
-special nucleotide sequence making beginning of gene
-what RNA polymerase binds to when mRNA is being formed in transcription
what are introns?
-segments of mRNA that do not code for a protein and are removed in splicing
what are extrons?
-segments of mRNA that do code for a protein and are spliced together after introns are removed
what happens to the created/processed mRNA molecule after transcription?
-it passes from nucleus (formation and processing spot) to the cytoplasm so it can be translated into amino acids and eventually a protein
why are all genes not expressed in every cell?
-not every cell needs to express every gene
-most cells have a specialized fucntion that only requires certain genes to be expressed
what is the process of repressor?
-a regulatory gene outside the operon code for a repressor
-repressor binds to operator
-transcription of the gene for that specific gene cannot take place bc it makes it so RNA polymerase cannot bind to the promoter
ex. lac operon normally binds to operator which lies next to promoter, when repressor is attache dto the operator, transcriptoin of the lactose0metabolizing genses does not take place bc RNA polymerase cannot bind to the promoter, if lactose is present than the shape of the repressor changes after lactose binds to it and it is no longer able to bind to the promoter, so the RNA polymerase can.
what are the three steps of translation?
-initiation
-elongation
-termination
describe the initation phase of translation
-mRNA binds to small ribosomal subunit of ribosome
-large subunit joins to small
describe the elongation phase of translation
-peptide (chain) lengthens one amino acid at a time
describe the termination phase of translation
-one of three stop codons is reached (UAA, UAG, or UGA)
-release factor binds to it and causes ribosomal subunits and mRNA to dissociate
-complete polypeptide is released
how does chromatin condensation regulate genes?
-keeps genes turned on or off
-the more tightly chromatin is condensed the less genes are expressed
-heterochramatic = darkly stained portionsof chromatin representing tight compaction
-once they become less tightly compacted they are euchromatin, active genes
-these still need further modification before they can be transcribed (no histones can be present)
how does DNA transcription regulate genes?
-DNA binding proteins that help RNA polymerase and dramatically speed up translation bind to a promoter
-several needed for transcription form complex that helps full part DNA and position RNA polymerase
how does mRNA processing regulate genes?
-removal of intron and splicing of extrons
-alternative mRNA processing- primary mRNA can produce different protein accoridng to which extrons are spliced together to create mature mRNA
how does mRNA tranlation regulate genes?
-cytoplasm contians proteins controlling whether translation takes place
-ex. IF-2 inhiibts start of protein synthesis when phosphoylated by kinase protein
-environmental factors can delay translation
-ex. red blood cells do not produce hemoglobin unless heme, iron containing group is available
-also hormones and poly-A tails determine ow long mRNA remains active for translation
