APS138 Cell And Molecular Biology - Scholes Flashcards
How many chromosomes do humans have?
46 (23 pairs)
What is unique about nucleic acids?
They can direct their own replication
When was the chemical composition of DNA discovered?
Late 1800s.
Friedrich Miescher isolated DNA in 1874
In 1881 Albrecht Kossel isolated the nucleotide bases
Actual structure worked out in 1953
Rosalind Franklin’s X-ray crystallographic images of DNA enabled Watson to deduce…
- That DNA was helical
- The width of the helix
- The spacing of the nitrogenous bases
- Double helix made of 2 strands
DNA is a polymer of nucleotides, each consisting of:
- A nitrogenous base (A,T,C or G)
- A phosphate group
- A deoxyribose sugar
What does 5’ refer to?
The specific carbon of the sugar molecule which the P group is attached to
What does 3’ refer to?
The carbon in the sugar molecule with the -OH group
What are the purines? How many organic rings do they have?
Adenine and Guanine.
2 rings
What are the pyramidines? How many organic rings do they have?
Cytosine and Thymine (and Uracil). 1 single ring.
How many hydrogen bonds does A pair to T with?
C to G?
2 bonds A to T, 3 bonds C to G
What direction do the 2 DNA strands run in?
An antiparallel direction
What are the base pairs on the 2 DNA strands?
complementary
Each ‘daughter’ DNA molecule consists of one …… strand and one …… strand
Parental, New
What is the model of DNA replication?
Semi-conservative
Each nucleotide that is added to a growing strand of DNA is a…
Nucleoside triphosphate (e.g. dATP, dTTP etc.)
DNA polymerases add nucleotides only to he free …. end of a growing strand. Therefore a new DNA strand can only elongate in the ….. direction.
3’
5’ to 3’
How long can E. coli’s 4.6 million nucleotide pair genome take to be replicated?
~1 hour
In eukaryotes each double helical DNA molecule is packages into a…
Chromosome within the nucleus
DNA replication begins at sites called…
Origins of replication
How many origins of replication are there in the circular of E. coli?
Only 1
What is an origin of replication?
A short stretch of DNA with a particular sequence of bases. Parental strands separate at the origin forming a replication bubble with a fork at each end.
What types of enzymes catalyse the synthesis of new DNA at a replication fork?
DNA polymerases
Which proteins participate in the unwinding of parental DNA strands?
Topoisomerases (correct overwinding), helicases (untwist double helix), single strand binding proteins (stabilise single stranded DNA)
What is the initial nucleotide strand in DNA replication called?
An RNA primer
What does the enzyme primase do?
Starts an RNA chain from scratch, adding RNA nucleotides one at a times using the parental DNA template.
To elongate the new strand, called the …… strand, DNA polymerase must work in the direction ….. the replication fork
Lagging
Away from
The lagging strand is synthesised as a series of fragments called….
Okazaki fragments
What does DNA pol I do?
Replaces RNA primer with DNA nucleotides
Which enzyme joins together the Okazaki fragments?
DNA ligase
What are telomeres?
DNA at the end of eukaryotic DNA molecules, consisting of multiple repetitions of one short nucleotide sequence. Prevents the shortening of DNA molecules and postpones he erosion of genes near the ends of DNA molecules
What has it been proposed that the shortening of telomeres is connected to?
Ageing - telomeric DNA tends to be shorter in dividing somatic cells of older individuals
Which enzyme catalyses the lengthening of telomeres in germ cells?
Telomerase
What is the region of a bacterial cell in which “supercoiled” DNA is found?
Nucleoid
What proteins are responsible for the first level of packing in chromatin?
Histones
The nucleosome consists of DNA wound twice around a protein core composed of …..
2 molecules of each of the 4 main histone types
What do the histone tails of one nucleosome interact with?
The linker DNA and nucleosomes on either side. A fifth histone is involved
What is gene expression? How many stages are there?
The process by which DNA directs protein synthesis. There are 2 stages: transcription and translation
What does transcription produce?
messenger RNA (mRNA)
What is translation?
The production of a polypeptide using information in mRNA
Where does translation occur?
At ribosomes
What is the sugar found in RNA?
ribose
What is Thymine replaced by in RNA?
Uracil
How many strands does RNA usually have?
One
What does the fact that prokaryotes lack nuclei mean for transcription and translation?
They can occur simultaneously (translation of mRNA can begin before transcription has finished) - ribosomes attach to the leading strand of an mRNA molecule while transcription is still in progress
What does the transcription of a protein coding gene result in in eukaryotes?
pre-mRNA
Modified through processing to yield finished mRNA