Unit 6 - topic 3 Flashcards
proteins
polypeptides made up of amino acids
amino acids are linked by
peptide bonds
gene expression
- process by which DNA directs the synthesis of proteins
- includes two stages: transcription and translation
- occurs in all organisms
transcription
- synthesis of RNA using information from DNA
- allows for the “message” of DNA to be transcribed
- occurs in nucleus
translation
- synthesis of a polypeptide using information from RNA
- a nucleotide sequence becomes an amino acid sequence
- occurs at the ribosome
messenger RNA
synthesized during transcription using a DNA template
mRNA carries information from DNA (nucleus) to
ribosomes in cytoplasm
transfer RNA molecules are important in the process of
- translation
- each tRNA can carry a specific amino acid
tRNA can attach to mRNA via
- their anticodon
- a complementary codon to mRNA
- allow information to be translated into a peptide sequence
ribosomal RNA
- rRNA helps form ribosomes
- helps link amino acids together
DNA contains the
sequence of nucleotides that codes for proteins
sequence is read in groups of three called the triplet code
during transcription
only one DNA strand is being transcribed
known as the template strand (aka the noncoding strand, minus strand, or antisense strand)
mRNA molecules formed are
antiparallel and complementary to the DNA nucleotides
base pairing
A-U and C-G
mRNA nucleotide triplets are called
codons
codons code for
amino acids
amino acid chart
64 different codon combinations
61 code for amino acids
3 are stop codons
universal to all life
redundancy
more than one codon codes for each amino acid
reading frame
codons on the mRNA must be read in the correct groupings during translation to synthesize the correct proteins
three steps in transcription
- initiation
- elongation
- termination
initiation
- RNA polymerase molecules attach to a promoter region of DNA
- do not need a primer to attach
promoter regions are
upstream of desired gene to transcribe
initiation eukaryotes
- promoter region is called TATA box
- transcription factors help RNA polymerase bind
initiation prokaryotes
RNA polymerase can bind directly to promoter
elongation
- RNA polymerase opens the DNA and reads the triplet code of the template strand
moves in the 3’ to 5’ direction
mRNA transcript elongates 5’ to 3’ - RNA polymerase moves downstream
only opens small sections of DNA at a time
pairs complementary RNA nucleotides
growing mRNA strand peels away from the DNA template strand
DNA double helix then reforms - a single gene can be transcribed simultaneously by several RNA polymerase molecules
helps increase the amount of mRNA synthesized
increases protein production
termination prokaryotes
- transcription proceeds through a termination sequence
- causes a termination signal
- RNA polymerase detaches
- mRNA transcript is released and proceeds to translation
- mRNA does NOT need modifications
termination eukaryotes
- RNA polymerase transcribes a sequence of DNA called the polyadenylation signal sequence
- codes for a polyadenylation signal (AAUAAA)
- releases the pre-mRNA from the DNA
- must undergo modifications before translation
three modifications that must occur to eukaryotic pre-mRNA
- 5’ cap
- Poly-A tail
- RNA splicing
5’ cap (GTP)
5’ end of the pre-mRNA receives a modified guanine nucleotide “cap”
Poly-A-tail
3’ end of the pre-mRNA receives 50-250 adenine nucleotides
both the 5’ cap and the poly-A tail function to
- help mature mRNA leave nucleus
- help protect mRNA from degradation
- help ribosomes attach to the 5’ end of mRNA when it reaches the cytoplasm
RNA splicing
sections of the pre-mRNA, called introns, are removed and then exons are joined together
introns
intervening sequence, do not code for amino acids
exons
expressed sections, code for amino acids
alternative splicing
a single gene can code for more than one kind of polypeptide
once all modifications have occurred, pre-mRNA is now considered
mature mRNA and can leave the nucleus and proceed to the cytoplasm for translation at the ribosomes
