Molecular Genetics Part II

Flashcards on RNA, mRNA, tRNA, rRNA, ribosomes, translation, and transcription

one-gene/one-polypeptide hypothesis

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(Textbook)

a proposal that one gene codes for one polypeptide (or protein)

messenger RNA (mRNA)

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(Textbook)

RNA that contains the genetic information of a gene and carries it to the protein synthesis machinery; it provides the information that determines the amino acid sequence of a protein

genetic code

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(Textbook)

a set of rules for determining how genetic information in the form of a nucleotide sequence is conerted to an amino acid sequence of a protein; a code specifying the relationship between a nucleotide codon and an amino acid

tripley hypothesis

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(Textbook)

a proposal that the genetic code is read three nucleotide bases at a time

gene expression

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(Textbook)

the transfer of genetic information from DNA to RNA to protein

transcription

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(Textbook)

the synthesis of RNA from a DNA template

translation

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(Textbook)

the synthesis of protein from an mRNA template

RNA polymerase

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(Textbook)

the main enzyme that catalyzes the formation of RNA from a DNA template

promoter region

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(Textbook)

a sequence of nucleotides in DNA that indicates where the RNA polymerase complex should bind to initiate transcription

precursor mRNA (pre-mRNA)

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(Textbook)

mRNA that has not undergone processing

mature mRNA

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(Textbook)

mRNA that has undergone processing

5’ cap

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(Textbook)

modified form of a G nucleotide; added to the 5’ end of an mRNA

3’ poly-A tail

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(Textbook)

a series of A nucleotides added to the 3’ end of mRNA

splicing

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(Textbook)

in mRNA, a process of excising out the introns and combining in the exons

transfer RNA (tRNA)

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(Textbook)

an RNA molecule that links the codons on mRNA to the corresponding amino acid for protein synthesis

anticodon loop

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(Textbook)

a triplet of bases positioned at one end of a tRNA that recognizes and base-pairs with a codon on mRNA during protein synthesis

acceptor stem

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(Textbook)

the 3’ end of a tRNA molecule that is the site of a attachment for a particular amino acid, based on the anticodon

aminoacyl-tRNA synthetase

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(Textbook)

an enzyme responsible for attaching an amino acid to a tRNA

ribosome

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(Textbook)

a cell structure composed of proteins and rRNA that provides the site where protein synthesis occurs

ribosomal RNA (rRNA)

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(Textbook)

the RNA that is associated with proteins in the ribosome

polyribosome

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(Textbook)

a structure composed of multiple ribosomes along a strand of mRNA

start codon

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(Textbook)

a triplet of three bases that specifies the first amino acid of a protein

Reading frame

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(Textbook)

collectively, the codons of mRNA that are read to produce an amino acid sequence; it is set by the start codon

peptide bond

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(Textbook)

a covalent bond formed between two amino acids during protein synthesis

mutation

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(Textbook)

a permanent change in the nucleotide sequence of a cell’s DNA

single-gene mutation

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(Textbook)

a mutation that involves changes in the nucleotide sequence of one gene

chromosome mutation

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(Textbook)

a mutation that involves changes in chromosomes, and may involve many genes

Point mutation

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(Textbook)

a mutation involving a single base pair substitution, insertion, or deletion

frameshift mutation

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(Textbook)

a mutation caused by the addtion or deletion of a number of nucleotides not divisible by three, resulting in a change in the reading frame

Silent mutation

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(Textbook)

a mutation that does not change the amino acid sequence of a protein

missense mutation

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(Textbook)

a mutation that changes the amino acid sequence of a protein

nonsense mutation

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(Textbook)

a mutation that shortens a protein by introducing a stop codon

transposon

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(Textbook)

a short segment of DNA capable of moving within the genome of an organism; also called a jumping gene

mutagen

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(Textbook)

an event or substance that increases the rate of changes to the DNA sequence of an organism’s genome

Why can DNA not leave the nucleus?

it is too large

What is DNA?

* contains 4 nitrogen bases
* is the code for all proteins that are made in the cell

What are genes made of?

DNA

What is a gene?

the coded DNA instructions that controls the production of specific proteins

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eg. enzymes, structural proteins, & oxygen-carrying proteins

What does the DNA inherited by an organism dictate?

the synthesis of certain proteins

What are proteins?

the link between genotypes and phenotypes

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* proteins made will determine the traits that show up in the offsprings

What is gene expression?

the process by which DNA directs the synthesis of proteins

What are the two stages of gene expression?

1. Transcription
2. Translation

What are the buiding blocks of proteins?

amino acids

how many amino acids are there?

20

how many nucleotides are there?

four

What specifies each amino acid?

three nucleotides in a sequence

how many possible combinations of amino acids are there?

64

What is each triplet of nucleotides called?

a codon

what does each codon call for?

a specific amino acid

How is a protein made?

when many amino acids are linked together

Which codons do not code for any amino acids?

1. “Start” codon
2. “Stop” codon

What is a “Start” codon?

a specific sequence of nucleotides that indicates where the protein-building instructions begin

What is a “Stop” codon?

act as signals for the end of a protein chain

How many codons are in a gene?

a gene on a chromosome contains many.

* each gene is the code for a particular protein

What do genes do?

provide the instructions for making specific proteins

do genes build proteins directly?

no

What is the bridge between DNA and protein synthesis?

RNA

What are the differences between DNA and RNA?

1. RNA is a single strand. DNA is a double strand
2. the sugar in RNA is ribose. The sugar in DNA is dexyribose
3. In RNA, uracil pairs with adenine. In DNA, thymine pairs with adenine

where are proteins made?

in the ribosomes (in the cytoplasm)

What determines which proteins need to be made?

DNA

A gene on the DNA molecule is ________

copied

What is the copy from the DNA molecule called?

RNA

What does the copy of DNA do?

copy of the DNA instructions is sent out to the ribosomes, in the cytoplasm

What does RNA carry?

the message from the DNA (in the nucleus) to the ribosomes (in the cytoplasm)

what does RNA ‘tell’ the ribosomes to do?

which proteins to make and how to make them

What are the three different types of RNA?

1. mRNA
2. tRNA
3. rRNA

Messenger RNA travels from….

the nucleus to the cytoplasm (ribosomes) with the instructions for making proteins

which type of RNA is the messenger between the DNA in the nucleus and the ribosomes in the cytoplasm?

mRNA

How are instructions carried by mRNA?

in the form of codons

What is the first codon on mRNA called?

“Start” codon

What happeneds when mRNA attches to the ribosome?

The ‘start’ codon will tell the ribosome where the protein-building instructions begin

What is the rest of the amino acids composed of (not the beginning or end, the middle)

a sequence of nucleotides that dictates the sequence of amino acids for the particular protein that is being made

What is the last codon called?

the ‘stop’ codon

what does the ‘stop’ codon tell the ribosome?

to stop the production of the protein

What does each transfer RNA have?

an anticodon at one end and an amino acid binding site at the other end

The base composing the anticodon are ______________ to the mRNA codons

complementary

what does tRNA do?

reads the message carried by mRNA and gathers the amino acids for making the protein

What does tRNA transfer?

amino acids from the cytoplasmic pool of amino acids to a ribosome

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* one end of the tRNA attaches to one animo acid and carries it to the ribosome

What does the cell have in stock?

20 amino acids in the cytoplasm

Where is ribosomal RNA found?

in the ribosomes

What is the use of rRNA?

used to bind mRNA and the tRNA to the ribosome.

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* this allows all components required for the synthesis of the proteins to be held together

What is transcription?

the process of forming a strand of RNA from a strand of DNA

where does transcription occur?

in the nucleus

what must the cell do to make proteins?

make RNA to send to the cytoplasm to tell the ribosomes which proteins to make

Messenger RNA is what…

a faithful copy of a gene’s protein building instructions

what enzyme is used to catalyze transcription?

RNA polymerase

What is the purpose of transcription?

to copy one gene from the DNA molecule

How do you know where one gene ends and another begins?

1. promoter
2. terminator

what is a promoter?

a DNA sequence where RNA polymerase attaches and initiates transcription

What is a terminator?

the DNA sequence that signals the end of transcription

What are the steps of transcription?

1. RNA polymerase binds to a site on the DNA molecule called the promoter
2. RNA polymerase seperates the DNA strands
3. One strand of DNA is used as a template (antisense) while the other is used for coding (sense)
4. new nucleotides are inserted according to the base pairing rules. A + U , C + G
5. this continues until the terminator is reached
6. the RNA polymerase moves along the DNA molecule, hydrogen bonds between the two strands of DNA are reformed
7. a single stranded RNA molecule has been transcribed

Important note on Transcription:

the purpose of transcription is not to copy the entire length of the DNA molecule, but to copy only one single gene.

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* the mRNA transcript will be sent to the ribosome as the instructions for protein sythesis

what must first happen to the RNA before it goes to the cytoplasm?

must be modified before it is ready to serve its purpose

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* mRNA is a small section of DNA

What is mRNA composed of?

1. introns
2. exons

What are introns?

small sequences of nitrogen bases that are not involved in the making of the protein

What must happen to the introns?

must be cut out of the RNA before it goes to the ribosomes

what are exons?

sequences of nitrogen bases that are involved in the making of the protein

what happends when mRNA is formed?

* both the intronss and the exons are copied from the DNA
* introns are cut out while RNA is still inside the nucleus

what happens to the remaining exons?

they are spliced back together to form the final RNA

what must be added to the new RNA?

* a cap & tail
* Cap helps identify the front end from the back end
* cap and tail help the ribosomes identify the start of the instructions and the end of the instructions