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Biology -biological molecules > Nucleic acids > Flashcards

Nucleic acids Flashcards

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1
Q

what does DNA?

A

Deoxyribonucleic acid

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2
Q

what does RNA stand for?

A

ribonucleic acids

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3
Q

what are DNA and RNA both needed for?

A

to build proteins

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4
Q

what’s the difference between the function of DNA and RNA?

A

DNA-
to hold or store genetic information
- the molecule that contains the instructions for the growth and development of all organisms

RNA-
to transfer the genetic code found in DNA out of the nucleus and carry it to the ribosomes in the cytoplasm
(ribosomes are where proteins are produced)

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5
Q

What are DNA and RNA both made up of?

A

nucleotides

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6
Q

what are DNA nucleotides made up of?

A

-a deoxyribose sugar with hydrogen at the 2’ position

-a phosphate group

-4 nitrogenous bases-
adenine(A)
cytosine(C)
guanine(G)
thymine(T)

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7
Q

what are RNA nucleotides made up of?

A

-a ribose sugar with a hydroxyl (OH) group at the 2’ position

-a phosphate group

-4 nitrogenous bases
adenine(A)
cytosine(C)
guanine(G)
uracil(U)

the presence of the 2’ hydroxyl group makes RNA more susceptible to hydrolysis
- this is why DNA is the storage molecule and RNA is the transport molecule with a shorter molecular lifespan

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8
Q

what are the two structural forms that the nitrogenous bases occur in?

A

Purines - adenine, guanine
they have a double ring structure

Pyrimidines- cytosine, thymine, uracil
they have a single ring structure

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9
Q

how do nucleotides become polynucleotides?

A

Separate nucleotides are joined via condensation reactions
- these condensation reactions occur between the phosphate group of one nucleotide and the pentose sugar of the next nucleotide

a condensation reaction between two nucleotides forms a phosphodiester bond
- between phosphate group and two ester bonds
(phosphate with double bond oxygen attached- oxygen- carbon)

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10
Q

what is the sugar- phosphate backbone?

A

the chain of alternating phosphate groups and pentose sugars produced as a result of many phosphodiester bonds?

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11
Q

DNA-
description of polynucleotide strands

A

DNA made up of two polynucleotide stranded lying side by side running in opposite directions
-the strands are ANTI PARALLEL

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12
Q

what is each DNA polynucleotide strand made up of?

A

Made up of alternating deoxyribose sugars and phosphate groups bonded together to form the sugar-phosphate backbone
bonds= phosphodiester bonds - covalent bonds

— the phosphodiester bonds link the 5- carbon of one deoxyribose sugar molecule to the phosphate group from the same nucleotide, which is itself linked by another phosphodiester bond to the 3-carbon of the deoxyribose sugar molecule of the next nucleotide in the strand

each DNA polynucleotide strand is said to have a 3’ end and a 5’ end
(these numbers relate to which carbon on the pentose sugar could be bonded with another nucleotide)

as the strands run in opposite directions (they are anti parallel), one is know as the 5’ to 3’ strand and the other is known as the 3’ to 5’ strand

the nitrogenous bases of each nucleotide project out from the back home towards the interior of the double stranded DNA molecule

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13
Q

where does hydrogen bonding come into play in DNA ?

A

the two antiparallel DNA polynucleotide strands are held together by hydrogen bonds between the nitrogenous bases

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14
Q

which base pairs are bonded by hydrogen bonding in DNA?

A

(purine) Adenine
+
(pyrimidine) Thymine
=2 hydrogen bonds

(purine) Guanine
+
(pyrimidine) Cytosine
= 3 hydrogen bonds

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15
Q

what is DNA described as?

A

double helix

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16
Q

how many polypeptide chains ins ENA made up of?

A

one- single stranded

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17
Q

what is each RNA polynucleotide strand made up of?

A

Alternating ribose sugars and phosphate groups linked together

18
Q

what is the length of RNA compared to DNA?

A

relatively short

19
Q

what happened in 1953 with the research on DNA?

A

Watson and Crick confirmed the double helix structure of DNA using Rosalind Franklins X-ray data

20
Q

why does a parent cell before it’s division need to copy the DNA contained within it?

A

so that the two new daughter cells produced will both receive the full copies of the parental DNA

21
Q

in what process is DNA copied via?

A

semi- conservative replication

22
Q

why is the process of DNA replication called semi-conservative?

A

In each new DNA molecule produced,
one of the polynucleotide DNA strands
(half of the new DNA molecule)
is from the original DNA molecule being copied

the other polynucleotide DNA strand
(the other half of the new DNA molecule)
has to be newly created by the cell

therefore the new DNA molecule has conserved half of the original DNA and then used this to create a new strand

23
Q

when does DNA replication occur?

A

it occurs in preparation for mitosis, when a parent cell divides to produce two genetically identical daughter cells
- each daughter cell contains the same number of chromosomes as the parent cell, the number of DNA molecules in a parent cell must be doubled before mitosis takes place

DNA replication occurs during the S phase of the cell cycle
(during interphase- when cell not dividing)

24
Q

when does DNA replication occur?

A

it occurs in preparation for mitosis, when a parent cell divides to produce two genetically identical daughter cells
- each daughter cell contains the same number of chromosomes as the parent cell, the number of DNA molecules in a parent cell must be doubled before mitosis takes place

DNA replication occurs during the S phase of the cell cycle
(during interphase- when cell not dividing)

25
Q

what is the process of semi conservative replication?

A
  • the enzyme helicase unwinds the DNA double helix by breaking the hydrogen bonds between the base pairs on the two antiparallel polynucleotide DNA strands to form two single polynucleotide DNA strands

each of thyou se single polynucleotide DNA strands acts as a template for the formation of a new strand made from free nucleotides that are attracted to the exposed DNA bases by base pairing

the new nucleotides are joined together by DNA polymerase which catalyses condensation reactions to form a new strand

the original strand and the new strand joined together through hydrogen bonding between base pairs to form the new DNA molecuke

26
Q

What type of nucleotides are found in the nucleus?

A

free nucleotides
- contain three phosphate groups

nucleoside triphosphates
‘activated nucleotides’

the extra phosphates activate the nucleotides, enabling them to take part in DNA replication

27
Q

how does DNA polymerase synthesise new DNA strands from the two template strands?

A

It catalyses condensation reactions between the deoxyribose sugar and phosphate groups of adjacent nucleotides within the new strand
- creating the sugar- phosphate backbone of the new DNA strands

DNA polymerase cleaves (breaks off) the two extra phosphates and uses the energy releases to recreate the phosphodiester bonds
(between adjacent nucleotides)

Hydrogen bonds then form between the complementary base pairs of the template and new DNA strands

28
Q

what does the 3’ end and 5’ end mean?

A

these numbers relate to which carbon on the pentose sugar could be bonded with another nucleotide

29
Q

in which way does DNA polymerase build the new strands?

A

It can only build it in one direction
5’ to 3’

As DNA is unwound from the 3’ towards the 5’ end, DNA polymerase will attach to the 3’ end of the original strand and move towards the replication fork
(the point at which the DNA molecule is splitting into two template strands)

this means that DNA polymerase enzyme can synthesise the leading strand continuously

30
Q

what is the leading strand?

A

the template strand the DNA polymerase attaches to

31
Q

what is the lagging strand?

A

the other template strand created during DNA replication

32
Q

How does DNA polymerase work on the lagging strand?

A

DNA polymerase moves away from the replication fork
5’ end to the 3’ end

this means the DNA polymerase enzyme can only synthesise the lagging DNA strand in short segments
(okazaki fragments)

33
Q

how do the short segments of DNA created by DNA polymerase on the lagging strand get joined together?

A

A second enzyme known as DNA ligase
hounds the lagging strand segments together to form a continuous complimentary DNA strand

It does this by catalysing the formation of phosphodiester bonds between the segments to create a continuous sugar-phosphate backbone

34
Q

in which way can nucleotides be added?

A

5’—>3’

35
Q

who were watson and crick?

A

two scientists who worked together to confirm the double- helix structure of DNA in 1953

36
Q

what did watson and crick come up with?

A

watson and crick also came up with a model by which DNA might be replicated:

this theory was called semi conservative DNA replication
the theory is based upon the specific hydrogen bonding between pairs of nitrogenous bases
( A+T and C+G)
being used during replication to conserve the genetic sequence

37
Q

what did watson and crick come up with?

A

watson and crick also came up with a model by which DNA might be replicated:

this theory was called semi conservative DNA replication
the theory is based upon the specific hydrogen bonding between pairs of nitrogenous bases
( A+T and C+G)
being used during replication to conserve the genetic sequence

38
Q

who proved watson and cricks theory to be correct?

A

Me seldom and Stahl

39
Q

what did meselson and stahl use to prove watson and cricks theory?

A

they used bacteria and two nitrogen isostopes,
a heavy form (15N)
and the normal, lighter form (14N)

40
Q

Meselsons and Stahls experiment explained

A

Bacteria are brown in a broth containing the heavy (15N) nitrogen isotope
•DNA contains nitrogen in its bases
as the bacteria replicated, they used nitrogen from the north to make new DNA nucleotides

After some time, the culture of bacteria had DNA containing only heavy (15N) nitrogen

a sample of DNA from the 15N culture of bacteria was extracted and spun in a centrifuge
- this showed that the DNA contains the heavy nitrogen settled near the bottom of the centrifuge tube

the bacteria containing only 15N was then taken out of the 15N broth and added to a broth containing only the lighter 14N nitrogen
the bacteria were left for enough time for one round of DNA replication to occur before their DNA was extracted and spun in a centrifuge

41
Q

Meselsons and Stahls experiment results

A

If conservative replication had occured, the original template DNA molecules would only contain the heavier nitrogen and would settle at the bottom of the tube, whilst the new DNA molecules would contain the lighter nitrogen and would settle at the top of the tube

If semi- conservative replication had occured, all the DNA molecules would now contain both the heavy 15N and light 14N nitrogen and would therefore settle in the middle of the tube
(one strand of each DNA molecule would be from the original DNA containing the heavier nitrogen and the other (new) strand would be made using only the lighter nitrogen)

Meselson and Stahl confirmed that the bacterial DNS had undergone semi- conservative replication
-The DNA from this second round of centrifugation settled in the middle of the tube, showing that each DNA molecule contained a mixture of the heavier and lighter nitrogen isotopes
- If more rounds of replication were allowed to take place,
the ratio of 15N:14N would go 1:1 after the first round of replication, to 3:1 after the second and 7:1 after the third

Biology -biological molecules (9 decks)

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