chapter seventeen part one Flashcards
telomeres
special nucleotide sequences that have multiple repetitions of 1 short nucleotide sequence
- at end of linear DNA
what is aging associated with?
the loss/shortening of telomeres
what are telomeres regenerated with?
telomerase
where is telomerase active?
embryonic development/gametes, single-celled eukaryotes, some cancers
- not active in somatic cells
why do single-celled eukaryotes need telomerase?
their species can’t continue without it
Beadle/Tatum experiment/study
- Neurospora crossa - haploid species
- studied protein-coding genes for nutritional activity
- X-rayed to cause mutations, looked for mutants among survivors
- supported one gene-one enzyme theory
gene expression
process by which DNA directs synthesis of proteins or RNAs
what does reverse transcription use?
reverse transcriptase
- how retroviruses like HIV spread
language for DNA and RNA
nucleotides
language for proteins
amino acids
where does transcription and translation occur in prokaryotes?
tcr: cytosol
tsl: cytosol
where does transcription and translation occur in eukaryotes?
tcr: nucleus
tsl: cytosol
1 gene to 1 protein/enzyme/polypeptide hypothesis
better: RNA molecule
- gene can code for set of polypeptides or RNA molecules
2 steps of protein synthesis/gene expression
transcription and translation
transcription
synthesis of RNA from DNA
steps of RNA synthesis in transcription
- RNA polymerase cuts open DNA at promoter
- DNA read from 3’ to 5’, RNA assembled from 5’ to 3’
- stops at termination sequence
- RNA breaks free, DNA reseals
RNA polymerase
- pries 2 DNA strands apart
- joins RNA nucleotides complementary to DNA
- 10-20 DNA nucleotides exposed at once
what are sometimes needed to initiate transcription?
transcription factors
transcription initiation complex
transcription factors and RNA polymerase
promoter
TATA box
what is required in transcription that is also required in DNA synthesis?
template, nucleotides, RNA polymerase that starts de novo (helices activity), ssDNA binding proteins
what is not required in transcription that is required in DNA synthesis?
ligase, topoisomerase, sliding clamp protein
how many strands of DNA are transcribed
1
3 types of RNA
mRNA, tRNA, rRNA
mRNA
- dictates A.A. sequence (protein recipe/blueprint)
- carries genetic message from dNA to protein-synthesizing machines
tRNA
- transfers A.A. to ribosome for assembly
- A.A. on one end of structure, other end is nucleotide triplet complementary to codon on mRNA
rRNA
- combines w/ proteins to make ribosome workbench for translation
- transcribed in nucleolus
mRNA processing
- both end of primary pre-mRNA transcript altered, interior parts cut out/spliced
- eukaryotic only
5’ cap
- added to 5’ end after transcription of first 20-40 nucleotides
- contains methylated guanine
poly-A tail
- enzyme adds 50-250 more adenine nucleotides to 3’ end after RNA transcribed
introns
intervening sequences, cut out/removed by spliceosome
- noncoding
exons
spliced together to form mRNA by spliceosome
- eventually expressed
purpose of 5’ cap and poly-A tail
- facilitate export of mature mRNA from nucleus
- protect mRNA from degradation from enzymes
- helps ribosomes attach to 5’ end of mRNA once it reaches cytoplasm
