Flashcards in DNA Deck (29)
What material contains all of the genes that are responsible for expression of all of the traits that appear in humans and other organisms?
What is the structure of DNA?
A very large molecule that consists of 2 strands of deoxyribonucleotides linked together- each deoxyribonucleotide consists of 3 parts - a deoxyribose sugar, a phosphate group and a nitrogenous base. The backbone of the polymer strand is composed of deoxyribose alternating with a phosphate. A base is attached to each deoxyribose. The shape of DNA is like a ladder. The sugar and phosphate groups form the uprights and the bases form the rungs. Hydrogen bonds link the complementary bases in the adjacent strand together. The two strands of deoxyribonucleotides are intertwined and coiled into a structure called a helix (in this case a double-stranded helix)
What holds the two strands of DNA together?
The hydrogen bonds between the complementary bases of each strand. Adenine forms two hydrogen bonds to every thymine in the opposite strand. Guanine forms 3 hydrogen bonds to every cytosine in the opposite strand. These bonds are relatively weak but they are plentiful.
What is DNA replication? When does it occur within mitosis?
An exact copy of the nuclear DNA is made. This occurs during interphase. It takes place prior to mitosis or meiosis to produce the pair of joined sister chromatids.
What is the 1st step in replication of the DNA strand?
The double helix must be unzipped.... the enzyme DNA helicase breaks the hydrogen bonds that link the complementary bases of the adjacent strands and the DNA strands stand on their own.
What is the second step of DNA replication?
On each strand starting from the top, free nucleotides (containing the complementary base) are lined up along the intact nucleotides and DNA polymerase catalyzes the linking of these free nucleotides and the intact nucleotides.
What is the third step of replication?
The free nucleotides are then progressively joined to one another (as the sugars join to the phosphates) until a new complementary strand is assembled alongside each previously existing strand.
The fourth step of replication ?
After the end of each strand is reached, there will be two identical DNA double helix strands. Each contain an original mother strand and a newly formed complementary daughter strand.
Why is replication said to be semi conservative?
Since each DNA double helix conserves one of the original strands, the replication process is said to be semiconservative.
What determines the amino acid sequence for all of the proteins in your body?
The code found in DNA
What is a gene?
The section of a DNA molecule that determines the sequence of amino acids in a single polypeptide chain of a protein. Genes are portions of DNA that code for a particular protein.
What is transcription ?
A copy of the DNA strand is transcripted onto a mRNA strand. In order for proteins to be synthesized (formed from the linkage of amino acids) the genetic code must be copied from the DNA in the nucleus and sent to the ribosomes.
What is the location for protein synthesis?
The ribosomes within the cytoplasm
What happens in transcription?
Transcription is very similar to replication in that the double DNA helix is first unzipped and unwound. But instead of DNA nucleotides being brought in to bind with DNA, RNA nucleotides are brought in by RNA polymerase. The new RNA nucleotides are linked together in a similar fashion to the formation of new DNA. The difference being that only a single strand of RNA is formed. In other words, only one side of the DNA double helix is encoded at one time. The new single stranded RNA is known as messenger RNA (mRNA). After its formation the mRNA separates from the DNA strand and moves out of the nucleus to take the "message" to the ribosomes.
Where does mRNA go after being transcribed?
It carries its code to the ribosomes for protein synthesis?
What is the significance of the order of the bases on the mRNA strand?
The order of these bases determines the order of amino acids used in the protein sequence.
How many amino acids are there in our bodies ?
20 amino acids
What is the significance of having 3 bases in the code?
Because there are 20 amino acids used in our bodies, the four bases must be arranged in combinations that allow for 20 unique codes. Three bases in combination provide 64 possible codes, which is more than enough for each amino acid to have at least one unique code. Here are some of the combinations and what they signify:
AAU and AAC = Asparagine
AAA and AAG = Lysine
CAU and CAC = Histidine
GCU, GCC, GCA, and GCG = Alanine
UAA, UGA and UAG = "stop"
AUG = Methionine "start"
What is a codon?
A codon is the three letter triplet that codes for a specific amino acid in the sequence. Each codon will code for a specific amino acid; no codon will ever code for more than one amino acid. This prevents error in the synthesis of proteins.
What is translation?
The mRNA codon is translated to make proteins.
What is the importance of tRNA?
Transfer RNA brings the correct amino acids in an orderly fashion into the ribosomes based on the sequencing of codons for specific amino acids in the translation process.
What is an anticodon?
Located on the tRNA, an anticodon is the complementary triplet to the codon of the mRNA strand. The anticodon will bring with it the specific amino acid requested in the codon.
What links the correct amino acid to its tRNA carrier ?
Each amino acid is linked to its tRNA carrier by a specific enzyme called tRNA synthetase
Ribosomes are made up of ______ and _______.
Proteins and rRNA (ribosomal RNA )
What is meant by the initiation process?
In translation, this is when the ribosome attaches to the mRNA strand.Where the larger unit fits together with the smaller unit, a groove is formed that mRNA is able to slide through.
What is the first codon that is always activated in translation ?
The first codon to be activated is always AUG which initiates the process of protein formation. The tRNA that matches the AUG code has an anticodon of UAC and carries with it the amino acid methionine.
What is elongation ? When does this process end?
The process of adding amino acids to the growing polypeptide chain is called elongation. This process ends when a "stop code is reached on the mRNA"
What happens in termination ?
A stop code is reached and the newly formed protein strand is released. The ribosome dissociates into its two subunits and is free to bind to the mRNA at a different site. The ribosome slides along the mRNA strand until it locates an initiation codon and begins the formation of another protein.