Proteins are _______________ made up of _____________ ________
polypeptides, amino acids
Which bonds connect amino acids?
peptide
... [Show More] bonds
gene expression
the process by which DNA
directs the synthesis of proteins
What two stages are used to synthesize proteins?
transcription and translation (occurs in all organisms)
Describe the basic sequence from DNA to protein.
DNA -> transcription -> RNA -> translation -> protein
transcription
the synthesis of
RNA using information from DNA. (Allows for the "message" of
the DNA to be transcribed)
Where does transcription occur?
nucleus
Translation
the synthesis of a
polypeptide using information
from mRNA
(A nucleotide sequence
becomes an amino acid
sequence)
Where does translation occur?
ribosomes
What are the three key RNA molecules in transcription and translation?
mRNA (messenger RNA), tRNA (transfer RNA), and rRNA (ribosomal RNA)
What is mRNA's basic role in transcription?
Messenger RNA is synthesized during
transcription using a DNA template.
mRNA carries information from the DNA (at the
nucleus) to the ribosomes in the cytoplasm.
What is tRNA's basic role in transcription?
Each tRNA can carry a
specific amino acid.
Can attach to mRNA via their
anticodon (a complementary codon
to mRNA).
Allow information to be
translated into a peptide
sequence
What is rRNA's basic role in transcription?
rRNA helps form ribosomes and
help link amino acids together.
______ contains the sequence of nucleotides that
codes for proteins
DNA
Triplet code
sequence of 3 nucleotides that
codes for amino acids
How many DNA strands are transcribed in transcription? What are the strand(s) called?
Only one DNA strand called the template strand is transcribed.
Other names for the template strand
noncoding strand, minus strand, or
antisense strand
mRNA molecules formed
are _______________ and
______________ to the DNA
nucleotides
antiparallel, complementary
RNA base pairing
A=U, C=G (no thymine, U is uracil)
Codons
mRNA nucleotide
triplets that code for amino acids
How many different codons combinations? How many code for amino acids? How many stop codons?
64 different codon combinations.
61 code for amino acids.
3 are stop codons.
Universal to all life.
What is the start codon and what amino acid does it code for?
AUG, Methionine
AD
Redundancy
more
than one codon code
for each amino acid
Reading frame
the codons on the mRNA must be
read in the correct groupings during translation to
synthesize the correct proteins
What are the three steps of transcription and translation (they have the same names in transcription and translation)?
1. Initiation
2. Elongation
3. Termination
Describe initiation of transcription
Transcription begins when RNA polymerase molecules
attach to a promoter region of DNA. Do not need a primer to attach. Promoter regions are upstream of the desired gene to transcribe.
Describe the difference of initiation in transcription in eukaryotes and prokaryotes.
Eukaryotes: Promoter region is called TATA box and transcription factors help RNA polymerase bind.
Prokaryotes: RNA polymerase can bind directly to promoter.
Describe the steps of elongation in transcription (it's the same process for eukaryotes and prokaryotes).
- RNA polymerase opens the DNA and reads the triplet code of the template strand.
RNA polymerase moves in the 3' to 5' direction and the mRNA transcript elongates 5' to 3'.
- As RNA polymerase moves downstream, it only opens small sections of DNA at a time.
It pairs complementary RNA nucleotides and the 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 which increases protein production).
Describe termination of transcription in prokaryotes.
Transcription proceeds through a termination
sequence (causes a termination signal).
RNA polymerase detaches and the mRNA transcript is released and proceeds to
translation.
mRNA does NOT need modifications in prokaryotes!
Describe termination of transcription in eukaryotes.
RNA polymerase transcribes a sequence of DNA called the polyadenylation signal sequence which codes for a polyadenylation signal (AAUAAA).
Releases the pre-mRNA from the DNA
Must undergo modifications before translation in eukaryotes!!
What are three modifications that must occur to
eukaryotic pre-mRNA before it is ready for translation?
1. 5' cap
2. Poly-A tail
3. RNA splicing
5' cap
the 5' end of the pre-mRNA receives a
modified guanine nucleotide "cap"
Poly-A tail
the 3' end of the pre-mRNA receives 50-250
adenine nucleotides [Show Less]