Chapter 12.3-12.6 Flashcards
What sugar is in RNA?
Ribose
What sugar is in DNA?
Deoxyribose
What bases make up RNA?
Adenine, Guanine, Uracil, Cytosine
What bases make up DNA?
Adenine, Guanine, Thymine, Cytosine
How does the structure of RNA compare to that of DNA?
RNA is single stranded and isn’t in a helix, while DNA is double stranded with base paring and is in the shape of a helix.
What are the three major classes of RNA?
Messenger RNA (mRNA), Transfer RNA (tRNA), Ribosomal RNA (rRNA)
What does mRNA do?
It takes the message from the DNA in the nucleus to the ribosomes in the cytoplasm
What does tRNA do?
Transfers amino acids to the ribosomes
What does rRNA do?
Makes up the ribosomes (along with ribosomal proteins),where poly peptides are synthesized
Name the two major steps involved in synthesizing a protein?
Transcription and Translation
What happens during transcription?
DNA serves as a template for RNA formation. DNA is transcribed into another type of polynucleotide (RNA)
What happens during translation?
The mRNA transcript directs the sequence of amino acids in polypeptide
What kind of code is the genetic code?
A triplet code
Through what experiment did Marshall Nirenberg and J. Heinrich Matthei lay the groundwork for cracking the genetic code?
1) Found that a cellular enzyme could be used to construct synthetic RNA
2) Used synthetic RNA and found that it could be translated in a test tube that contains cytoplasmic contents of the cell
3) First synthetic RNA was composed of only uracil, foudn that the protein that resulted was UUU (Phenylalanine)
What are three important properties of the genetic code?
1) The genetic code is degernate, amino acids have more than one codon
2) The genetic code is unambiguous. Each triplet codon has only one meaning
3) The code has 1 start signal and 3 stop signals.
The universal nature of the genetic code provides further evidence for what?
That all living things share a common ancestor. This is why it is possible to transfer genes from one organism to another. However, scientists have found that genetic code used by mammalian mitochondria and chloroplasts are a bit different
What occurs during transcription?
A segment of DNA serves as a template for the production of an RNA molecue
What are the steps in the formation of mRNA?
1) Segment of DNA helix unwinds
2) Complementary RNA nucleotides pair with the DNA nucleotides on the strand of the opposite gene (known as the template strand, other strand is called the nontemplate strand)
3) RNA Polymerase joins the nucleotides together in the 5’–>3’ direction.
When does transcription begin?
When RNA polymerase attaches to a region of DNA called the promoter
What is the promoter?
Defines the start of transcription, the direction of transcription, and the strand to be transcribed
What process leads to the inhibition of transcription?
The binding of RNA polymerase to the promoter.
Complete this statement:: Elongation of the mRNA molecule continues until……
RNA polymerase comes to a DNA stop sequence. This stop sequence will cause RNA polymerase to stop transcribing the DNA and to release the mRNA molecule.
What is unedited mRNA called?
mRNA transcript
How are cells able to speed up the process of producing proteins?
This is because many mRNA polymerase molecules can be working to produce mRNA transcripts at the same time. This allows the cell to produce many copies of mRNA transcripts i a much shorter time
Right after the pre-mRNA is made, what does it recieve?
A cap and a poly A tail
What is the cap made up of/what does it do?
A modified guanine nucleotide that helps tell a ribosome where to attach when translation begins
What is the poly-A-tail made up of/what does it do?
A chain of 150-200 adenine nucleotides. Facilitates the transport of mRNA out of the nucleus and also inhibits degradation of mRNA by hydrolytic enzymes
What occurs when the pre m-RNA is edited?
The introns are removed by splisosomes and the extrons are pulled together.
Where are splisosomes found?
They are found in eukaryotic cells
Where are Ribozymes found?
They are found in prokaryotes, and they are enzymes that posses catalytic activity in the same manner as enzymes composed of protein.
What does the presence of introns allow the cell to do?
Pick and choose which exons will go into a particular mRNA
What is alternative mRNA spliciing?
The idea that mRNA can contain only some of the possible exons available from a DNA sequence
What are microRNAs? (miRNAs?)
Involved in regulating the translation of mRNAs. These molecules bond with mRNA through complementary base pairing and prevent translation from occuring
During meiosis, what does the presence of introns encourage?
It encourages crossing over during meiosis, and this promotes exon shuffling which plays a role in the evolution of new genes
Where does translation take place?
In the cytoplasm of eukaryotic cells
What happens during translation (general summary)
The sequence of codons in the mRNA at a ribosome directs the sequence of amino acids in a polypeptide
What is the role of tRNA?
(Transfer RNA)-transfers amino acids to the ribosomes
How does tRNA use it’s structure to accomplish it’s task?
tRNA is a single stranded nucelic acid that doubles back on itself to create regions where complementary bases are hydrogen honded to one another (The structure can be drawn as a flat cloverleaf)
What is an anticodon?
It is the group of three bases that is complementary to a specific mRNA codon
Why are there fewer tRNAs than codons?
What were Francis Crick’s observations with regards to the wobble hypothesis?
1) The first two positions in a tRNA anticodon pair obey the A-U/G-C configuration. The third position can be variable
2) Some tRNA molecules can recognize as many as four separate codons differing only in the third nucleotide
What does the wobble effect help ensure?
That despite changes in DNA base sequences, the correct sequence of amino acids will result in a protein
What do aminoacyl-tRNA synthases do?
They are enzymes that have a recognition site for the amino acid to be joined to a particular tRNA. This is an energy requiring process that uses ATP.
After the amino acid-tRNA complex is formed, where does it travel?
The ribosome
Describe the structure of the ribosome
Ribosomal RNA (rRNA) is produced from a DNA template in the nucelolus of a nucleus
- rRNA is packaged with a variety of proteins into two ribosomal subunits
- Subunits move into the cytoplasm and combine when translation begins
- Ribosomes can remain in the cytoplasm or become attached to endoplasmic reticulum
What is the function of a ribosome?
Protein synthesis
Ribosomes have a binding site for mRNA and 3 binding sites for tRNA. rRNA helps form polypeptides
