Biological molecules: DNA, RNA and protein synthesis Flashcards
(42 cards)
what is meant by point mutation?
a mutation affecting a single nucleotide
why is DNA replication semi conservative?
each DNA molecule contains one strand of the original DNA molecule and one brand new.
what is a nucleic acid?
large molecules discovered in the cell nuclei. The two types are RNA and DNA
nucleic acids are made of many nucleotides. What are the three components of a nucleotide?
-pentose sugar
-phosphate group
-nitrogenous base
how are nucleotides linked?
they are linked by condensation reactions to form a polynucleotide. The phosphate group on carbon 5 of the pentose sugar creates a covalent bond with the carbon 3 on the adjacent pentose sugar. This is called a phosphodiester bond which can be broken by hydrolysis
what is the pentose sugar called in DNA and RNA?
in DNA, the pentose sugar is called deoxyribose(one fewer oxygen) and in RNA, the pentose sugar is called ribose.
name the nitrogenous bases in DNA and RNA
in DNA, the nitrogenous bases are thymine, guanine, adenine and cytosine. It is the same as in RNA but thymine is replaced with uracil.
what are pyrimidines and purines?
pyrimidines are the smaller bases which contain single ring carbon structures. These are thymine and cytosine. Purines contain double ring carbon structures, these are adenine and guanine.
describe the structure of DNA
double helix and is anti-parallel as each strand has a phosphate group on one end and the other is a hydroxyl group, these strands run in opposite directions. Sugar phosphate backbone.
how are the nitrogenous bases paired?
COMPLEMENTARY BASE PAIRING-adenine and thymine form two hydrogen bonds but cytosine and guanine form three hydrogen bonds
why does a purine always pair with a pyrimidine?
so the distance between the sugar phosphate backbones is constant all down the DNA molecule.
what are the differences between RNA and DNA (3 points)?
-DNA is found in chromosomes, RNA is found in cytoplasm
-DNA is long but RNA is short
-DNA is double stranded but RNA is single stranded
Describe the first step of DNA replication
DNA helices cases hydrogen bonds the break between the complementary base pairs causing the two polynucleotide chains to separate.
In DNA replication what occurs after the two polynucleotide chains seperate?
free nucleotides line up with their complementary bases. At this stage, the DNA are only held by hydrogen bonds, not phosphodiester bonds. The free nucleotides are called activated nucleotides and they contain 3 phosphate groups.
In DNA replication, what occurs after the activated nucleotides line up with the original strand?
DNA polymerase moves down the molecule and catalyses the formation of phosphodiester bonds between the activated nucleotides which is an example of a condensation reaction. When phosphodiester bonds form, the two extra phosphate groups leave, providing more energy for the reaction.
what is a DNA mutation?
when an incorrect base is inserted causing the DNA sequence to change.
what is the role of messenger RNA?
to send instructions for protein synthesis from the genetic information of DNA.
what is discontinuous and continuous DNA replication?
Discontinuous replication is the synthesis of the new strand of a DNA molecule as a series of small fragment (nucleotides) are joined. Continuous replication is seen by the other strand (leading strand) where the continuous addition of nucleotides take place.
In the 1950s, what was the other way of DNA replication mentioned apart from semi-conservative replication?
conservative replication: DNA molecules is formed with two new strands, no original DNA strands.
Describe the experiment that took place, to determine whether DNA replication was conservative or semi-conservative
-A sample of bacteria was used. The nitrogen atoms would all be nitrogen 14. DNA is extracted which is placed in a solution and spun in a centrifuge. DNA moves down to a band which scientists can detect (higher). The position of the DNA band depends on how heavy the DNA is.
-next scientists cultured the bacteria in a growth medium where they can be replicated many times. Most of the nitrogen atoms were nitrogen 15- the band formed for this is near the bottom (lower)of the centrifuge.
-then a sample of bacteria with nitrogen 15 was transferred to the bacteria of nitrogen 14. It is replicated once. Using a centrifuge, this band was in between the bands go nitrogen 14 and 15 showing that the replicated DNA contain half of original and half new.
when the DNA was replicated twice, there were two bands, why?
4 strands are produced- two represent nitrogen 14 and two represent nitrogen 15
what is a codon?
a sequence of three bases (triplet code) which codes for an amino acid
what is a gene?
a section of DNA that contains the complete sequence of bases(codons) to code for an entire protein.
what are the three key features of the genetic code?
-degenerate, as a single amino acids can be coded from multiple codons
-universal, as every living organism has it
-non overlapping as no base is read more than once
