ch 9 Flashcards
Gene Expression
Protein Synthesis
list the differences between DNA and RNA
DNA
- double-stranded
- uses thymine
- has deoxyribose sugar ring
- located in the nucleus in Eukaryotes
- Contains information for making proteins
- longer
- 1 kind
RNA
- single stranded
- uses uracil
- has ribose sugar ring
- Moves from the nucleus to cytoplasm
- Uses information to make proteins
- shorter
- at least 3 kinds
Transcription
nucleotides in DNA info “transcribed” into nucleotides in mRNA, tRNA, and rRNA
describe Enzyme RNA polymerase
Enzyme RNA polymerase
- Binds to DNA at promoter (beginning) sequence site.
- Splits double helix by breaking hydrogen bonds between nitrogen bases
- Transcribes nucleotide sequences to mRNA substituting uracil for thymine.
- Stops at terminator sequence site (DNA helix hydrogen bonds reform)
In Eukaryotes, enzymes cut introns out of RNA and reconnect exons before mRNA leaves nucleus
Translation
nucleotides in mRNA are “translated” into amino acids in protein
Codon
sequence of 3 nucleotides; codes for 1 Amino acid
Codons nearly universal
almost all organisms use the same codons for the same amino acids…which means we all came from a common ancestor.
Translation steps:
- mMRA binds to smaller ribosomal unit – its start codon is at “P” site
- tRNA carrying its specific amino acid binds to start codon at the “P” site with its complementary anti-codon end
- Large ribosomal unit attaches to form fully functional ribosome
- next tRNA carrying its specific amino acid binds to next codon at “A” with its complementary anti-codon end
- a peptide bond is formed between the new and older amino acids
- tRNA at “P” detaches, leaving amino acid attached to amino acid attached to tRNA at “A” site
- mRNA and the attached tRNA at “A” and its attached amino acids move to “P” (shifts 1 codon length over - codon that was at “A” site now at “P” - a new empty one is at “A”)
- next tRNA carrying its specific amino acid binds to next codon at “A”….etc.
- Process continues until stop codon reached - when everything is released
Operon
cluster genes on DNA that code for proteins with related functions plus regulatory regions: promoter, operator
Promoter
region “upstream” of genes is the landing site for RNA polymerase
Operator
region of between promoter area of operon and coding genes.
where does RNA polymerase bind?
RNA polymerase binds to promoter region.
what happens if a repressor molecule is bound to the operator?
If repressor molecule is bound to operator the transcription of coding genes to mRNA is blocked and cannot proceed.
how is a repressor released?
Repressor released when inducer molecule binds to it.
Gene regulation in Eukaryotes:
Genes with related functions are scattered among chromosomes.
why can’t RNA polymerase bind to transcription site?
give an example
RNA polymerase cannot bind to transcription site without the presence of a cluster of proteins called transcription factors. Other proteins called the initiation complex bind to an enhancer site, which can be distant from gene transcription area and then it touches the transcription factors and RNA polymerase is released to transcribe.
Example: Estrogen hormone (controls secondary sex characteristics)
- Estrogen passes into cell and binds to receptor protein on nuclear envelope creating hormone-receptor complex
- Receptor complex binds to acceptor protein
- Acceptor protein binds to enhancer site which turns on transcription process for proteins related to secondary sex characteristics
Point mutations
change just one or a couple nucleotides
Substitution
one nucleotide substituted for another.
Insertions or deletions
one or more nucleotides added or deleted affecting all codons in sequence after point (frame shift)
Mutagens
environmental agents that may induce mutations
Carcinogen
cancer causing mutagen
Cancer
unrestricted cell growth.
Tumor
cancer cell growth area
Benign
does not invade surrounding tissues
