Unit 11 part 1 Flashcards
The Flow of Genetic Material
- DNA is inherited by an organism and due to the synthesis of proteins, this leads to expression of specific traits
- The information content of genes is in the specific sequences of nucleotides
- Proteins are the links between genotype and phenotype
gene expression
the process by which DNA directs protein syntehsis
- includes transcription and translation
RNA is the bridge between
genes and the proteins for which they code
Transcription
synthesis of RNA using information in DNA
* Transcription produces messenger RNA (mRNA)
Translation
synthesis of a polypeptide, using information in the mRNA
* Ribosomes are the sites of translation
- In prokaryotes: (gene expression)
translation of mRNA can begin before transcription has finished
in eukaryotic cell (gene expression)
nuclear envelope separates trnascription from translation
Eukaryotic RNA transcripts are modified through
rna processing to yield the finished mRNA
- a primary transcript is the initial RNA transcript from any gene prior to processing
central dogma
the concept that cells are government by a cellular chain of command
DNA -> RNA -> Protein
Flow of information from gene to protein:
- triplet code
triplet code
non overlapping, three nucleotide words
words of a gene
- transcribed into complementary non overlapping, three nucleotide words of mRNA
- WORDS IN MRNA ARE TRANSLATED INTO AMINO ACIDS, FORMING A POLYPEPTIDE
template strand:
- Provides a template for the sequence of complementary nucleotides in an mRNA transcript
- Non template strand:
- Nucleotides of this strand are identical to the codons, except U in RNA in place of T in the DNA
During translation, the mRNA triplets,
called codons, are read in the 5′ → 3′ direction
- each codon specifies the amino acid to be added ina. growing polypeptide
- from gene (DNA sequence) to protein (polypeptide sequence)
- Of the 64 triplets
- 61 code for amino acids
- 3 triplets are stop signals to end translation
redundant meaning
the genetic code is redundant
- more than one codon may specify a particular amino acid
an amino acid may have more than one code
the genetic code is non ambigious
- no codon specifies more than one amino acid
Wobble Hypothesis
Flexible pairing at the third base of a codon allows some tRNAs to bind to more than one codon
Cracking the Code
- Codons must be read in the correct reading frame to produce the specified polypeptide
Universal Genetic Code
- The genetic code is nearly universal:
- Shared by the simplest bacteria and the most complex animals
- Genes can be transcribed and translated after being introduced to a new species
Transcription
- Transcription is the first stage of gene expression
- DNA directed RNA synthesis
three stages of transcription
- initiation
- elongation
- termination
rna synetheis is catalyzed by
polymerase (not DNA polymerase)
RNA polymerase:
- Catalyzes RNA synthesis
- Opens DNA strands and joins RNA nucleotides together in 5’ – 3’ direction
- Does not need any primer
- Follows same base-pairing rules as DNA,
except that uracil substitutes for thymine - Produces RNA that is complementary to the DNA template strand
Promoter
DNA sequence where RNA polymerase attaches
* Transcriptional start point
* Usually extend several dozen nucleotides upstream of the start point
* A TATA box is crucial in forming the initiation complex in eukaryotes
transcription unit
the stretch of DNA that is transcribed
in bacteria the sequence signalling the end of trsnacription is called
terminator
- Transcription factors:
- Mediate the binding of RNA polymerase and the initiation
of transcription
- Transcription initiation complex:
- The completed assembly of transcription factors and RNA polymerase II bound to a promoter
As RNA polymerase moves along DNA,
it untwists the double helix, 10-20 bases at a time
* Transcription progresses at a rate of 40 nucleotides per second in eukaryotes
- Nucleotides are added to the
3′ end of the growing RNA molecule
termination- bacteria
the polymerase stops transcription at the end of the terminator
* mRNA can be translated without further modification
in eukaryotes- termination
RNA polymerase transcribes the polyadenylation (polyA) signal sequence;
* RNA transcript is released 10–35 nucleotides past this polyadenylation sequence
(bunch of AAAA in a row)
RNA processing
- enzymes in the eukaryotic nucleus modify pre-mRNA
- transcripts are then transported to the cytoplasm
- during RNA processing, both ends of the primary transcript are altered
Splicing
- Sections of mRNA(introns) are removed, and remaining sections (exons) are spliced together
- Each end of a pre-mRNA molecule is modified:
- 5’ ends recieve 5’ cap
- 3’ end gets poly-A-tail (AAAA)
modifications to the mRNA do what
- help export to cytoplasm
- protect mRNA from hydrotic enzymes
- help ribosomes attach to 5’ end
introns
non- coding regions
extrons
coding regions, expressed and usually translated into amino acid sequences (importnant ones)
