Chapter 3 - DNA structure and function Flashcards
describe the structure of DNA
DNA molecule is a double helix (two strands) which are joined together by weak hydrogen bonds between complimentary pairs of nitrogenous bases. The complimentary base pairing means that that adenine always pays with Thymine and cytosine always pairs with guanine. The two linear strands are opposite in direction to each other (anti-parallel).
what does a nucleotide consist of
a deoxyribose sugar, a phosphate group and a nitrogenous base.
what direction does DNA and RNA synthesis occur in
5’ to 3’ direction. 5’ end starts with a phosphate and the 3’ end finishes with a sugar
what are the differences between DNA and RNA
- In RNA, deoxyribose sugar is replaced with ribose sugar
- RNA has the nitrogenous base uracil while DNA contains thymine.
- RNA is single stranded
- DNA is a self-replicating molecule while RNA is synthesised from DNA (is a copy).
- DNA contains genetic code for the organism while RNA is a translator of the genetic code.
Why is DNA replication considered semi conservative
As one of the two strands is conserved from one generation to the next while the other strand is new
list the four main enzymes involved in DNA replication and their functions
- DNA polymerase: Synthesises new strands of DNA based on a template strand
- DNA helicase: enzyme that helps the two strands of DNA unwind and seperate by breaking the weak hydrogen bonds between corresponding nucleotides.
- DNA primase: Signals to polymerase where to start replication
- DNA ligase: enzyme used to catalyse the formation of phosphodiester bonds between two pieces of DNA. also joins together okazaki fragments
what is a genome
all the genetic material contained in an organism or cell
define DNA replication
The process a DNA molecule undergoes to make a complete and identical copy of itself, ready for cell division
what is an Okazaki fragment
a short fragment of DNA synthesised during DNA replication. Multiple fragments are joined together to make the lagging strand
coding DNA
The sections of DNA that code for a protein. Contain instructions that determine the order of the codons in the mRNA, which in turn determines the order of amino acids in a protein. Called exons
non coding DNA
All of the DNA sequences within a genome that are not found within mRNA coding exons. Include introns, have no known function. Are cut out before mRNA leaves the nucleus in pre-mRNA splicing
what are the steps of DNA replication
- DNA is unzipped by Helicase by breaking down weak hydrogen bonds between nucleotides
- Primase required to start replication.
- DNA polymerase binds to a single strand and builds a complementary strand (using free nucleotides in nucleus) 5’ to 3’ end
- ligase seals DNA fragments together
- DNA formed
what is transcription
(DNA –> mRNA) the synthesis of mRNA using the stored DNA code. DNA must be transcribed into mRNA while inside the nucleus as mRNA can fit through the nuclear pores
what is translation
(mRNA –> Amino acid) the synthesis of a polypeptide using the info in mRNA (a string of amino acids)
What are the steps of transcription
- RNA polymerase binds to a promoter region. It breaks the weak hydrogen bonds joining the complimentary nucleotides and unzips a portion of the double helix
- Moving along the template DNA strand in 3’ to 5’ direction, The RNA polymerase adds free-floating nucleotides to the growing mRNA sequence according to complementary base pair rules. In RNA uracil pairs with adenine. New strand of mRNA is synthesised in a 5’ to 3’ direction
- The DNA bases are in triplets, and the complimentary mRNA triplets produced a called codons. The process continues until there is a termination signal and the pre-mRNA is released
- Only the coding region (gene) of DNA is transcribed. Pre-mRNA consists of introns and exons. The introns are removed and the exons are joined to create mature mRNA. Mature mRNA then exits the nucleus via a nuclear pore
