Chapter 17 Flashcards
What are proteins composed of?
Amino acids
Describe the general formula of an amino acid.
Amino and carboxyl group (COOH), hydrogen, R group
How many different amino acids are commonly present in proteins?
20
Describe the characteristics of the different amino acids.
Six are nonpolar, one polar, and two are basic. The nine essential amino acids share a common essential characteristic: our body can’t produce by itself and requires a thorough intake of food.
What is an essential amino acid?
These amino acids are not produced by the body but must be included in the diet
What are the nine essential amino acids?
Lysine, Histidine, Tryptophan, Phenylalanine, Valine, Methionine, Leucine, Isoleucine, and Arginine.
What is the primary structure level of a protein?
the sequence of amino acids held together by peptide bonds
What happens to the amino acid chain as the protein is being formed?
As amino acids bind together through polypeptide bonds, they form a protein chain. Once that chain is completed, or a stop codon is reached, the protein is released into the cell to go wherever it needs and the chain gets longer in length.
What is the relationship between polypeptides and proteins?
When connected together by a series of peptide bonds, amino acids form a polypeptide, another word for protein.
Describe the process of transcription.
It is the process by which the information in a strand of DNA is copied into a new molecule of messenger (mRNA). It goes through a three-step process: initiation, elongation, and termination.
Where does transcription take place?
Transcription takes place in the nucleus.
What is produced during transcription?
One strand of mRNA (messenger RNA)
What enzyme transcribes mRNA?
RNA polymerase
What are transcription factors?
Transcription factors start the binding of RNA polymerase and initiation of transcription.
RNA polymerase
the key enzyme involved in creating an equivalent RNA copy of a sequence of DNA.
Template strand of DNA
Strand of DNA that RNA polymerase reads and transcribes.
Non-template strand of DNA
Strand of DNA that RNA polymerase isn’t transcribing
Describe the direction of a template strand of DNA relative to the mRNA transcript.
It reads from 5’ to 3’
Describe the process of translation.
Translation is the making of a polypeptide, using information in the mRNA. It also has a three-step process: initiation, elongation, and termination
Where does translation occur?
In the cytoplasm
What is produced during translation?
A polypeptide
Transcription in prokaryotes
mRNA is produced by transcription and is immediately translated with additional processing
Transcription in eukaryotes
The nucleus provides a separate compartment for transcription. The original RNA transcript pre RNA is processed in various ways before leaving the nucleus as mRNA.
What is the “central dogma of molecular biology?”
DNA -> RNA -> Protein
How can four nucleotides code for twenty amino acids?
It needs to have a triple code to have enough to fill the strand. (aka 4^3)
What are codons?
Three nitrogenous bases put together to represent amino acids.
How many nucleotides are there per codon?
3
start codon
AUG (met); where translation starters
stop codons
UGA, UAA, UAG; where translation stops.
Why is the genetic code redundant but not ambiguous?
multiple codons code for some amino acids, but no codons code for more than one amino acid
How does a segment of mRNA code for the sequence of amino acids in a protein?
The anticodon is complementary to the codon in messenger RNA.
What is the minimum number of nucleotides needed on the RNA strand to produce a polypeptide 26 amino acids long?
The minimum number would be 78 because you’d have to multiply the amino acids by three to get the total minimum number of nucleotides.
Describe the reading frame for the genetic code and how does a frameshift affect the reading frame?
Codons must be read in the correct groupings (groups of three). If it isn’t correct, there could be a malfunction or not a function at all.
Promoter
The DNA sequence where RNA polymerase attaches. It signals the transcription start point and usually extend several dozen nucleotide pairs upstream of the start point
TATA box
A promoter that is crucial in forming the initiation complex in eukaryotes. It is a DNA sequence that indicates where a genetic sequence can be read and decoded. Signals to “bind here”
Transcription factors
mediate the binding of RNA polymerase and the initiation of transcription. It attaches to the strand and separates. Bind to DNA strand during initiation.
RNA polymerase
gets the DNA strands apart and hooks together the RNA nucleotides.
Initiation
the attachment of molecules and spread of RNA. RNA polymerase has to bind to a promoter region that is adjacent to a gene. The start production of strand attachment includes RNA polymerase and transcription factors. After RNA polymerase binds to the promoter, the DNA strands unwind, and the polymerase initiates RNA synthesis at the start point on the template strand.
Elongation
It is lengthening the mRNA strand. It adds nucleotides to the transcript to produce all the code. As RNA polymerase moves along the DNA, it untwists the double helix and elongates the RNA transcript at 5’ to 3’. In the wake of transcription, the DNA strands re-form a double helix. Nucleotides are added to the 3’ end of the growing RNA molecule.
Termination
Eventually, the RNA transcript is released, and the polymerase detaches from the DNA. In bacteria, the polymerase stops transcription at the end of the terminator and the mRNA can be translated without further modification.
5’ cap
are on the 5’ end that receives a modified guanine nucleotide
UTR’s
It is the region RNA is not translated and not part of the production of proteins.
Polyadenylation signal
Signal before pre-mRNA is cut and released. It is AAUAAA.
Poly-A tail
The 3’ end. 50-250 adenine nucleotides are added
Introns
noncoding stretches of nucleotides that are intervening sequences. This is what is cut out and integrated back to RNA
Exons
expressed regions translated to protein and spliced together after introns are cut out
What is mRNA splicing?
removes introns and joins exons, creating an mRNA molecule with a continuous coding sequence.
Describe the process of RNA splicing with spliceosomes.
Spliceosomes slice the RNA. It consists of a variety of proteins and several small nuclear ribonucleoproteins (snRNPs) that recognize the splice sites.
Why is splicing necessary?
It is necessary because, without it, mRNA can’t be translated into a protein.
What are the advantages of RNA splicing?
It produces a mature mRNA and it allows many different transcripts to be made from the same stretch of genes.
What is a ribozyme?
RNA molecules that function as enzymes.
How are ribozymes used in the body?
Splicing may also be carried out by ribozymes
Where does translation occur?
ribosome
What is a ribosome?
Ribosomes facilitate specific coupling of tRNA anticodons with mRNA codons in protein synthesis.
What are a ribosome’s components?
The two ribosomal subunits (large and small) are made of proteins and ribosomal RNA (rRNA).
What are the “sites” within a ribosome?
A ribosome has a P site, A site, and E site.
Describe how ribosomes and various forms of RNA cooperate to translate mRNA into protein.
a molecule of mRNA is moved through a ribosome, codons are translated into amino acids. The interpreters are tRNA molecules with a specific anticodon on the end and a corresponding amino acid on the other end. tRNA adds its growing amino acids to a polypeptide chain.
Describe how tRNA moves through a ribosome during protein synthesis.
moves through a ribosome with the help of an aminoacyl- tRNA synthetase. The active site fits only a certain combination of amino acids and tRNA.
Describe how this process is terminated.
the process is terminated by the use of base triplets that act as signals to stop translation. A release factor binds directly to the stop codon on the A site. The release factor causes addition of a water molecule instead of an amino acid to the polypeptide chain.
What enzyme attaches amino acids to tRNA?
synthetase
What part of tRNA is complementary to the codons of mRNA?
anticodons
termination in prokaryotes
RNA polymerase II transcribes a sequence in the DNA polyadenylation signal sequence then at point 30-35 nucleotides downstream from AAUAAA proteins associated with the growing RNA transcript out of three from the polymerase releasing the pre mRNA
termination in eukaryotes
the transcribed terminator functions as the termination signal causing the polymerase to detach from the DNA and release the transcript.
What is a protein?
A polypeptide formed from an amino acid chain.
6 functions of protein
- Enzymes: speed up chemical reactions
- Storage: store amino acids
- Defensive: protect against disease
- Transport: transport substances across cell membrane or around body
- Structural: support within the cell
- Contractile/motor proteins: movement
