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A-level Biology > Module 2.3 > Flashcards

Module 2.3 Flashcards

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1
Q

DNA is built from molecules called nucelotides.

A

Structure of nuecleotide is found in DNA ,
-Dont need to know structure but check sheet .

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2
Q

But nucleotide consists of three parts and we do need to know these …

A

check sheet

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3
Q

What is in the center of the strucutre?

A

Contains a five-carbon sugar molecule.
-Sugars with 5 carbon atoms are called pentose sugars .

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4
Q

What is attached to the sugar ?

A

We find a nitrogen-containing molecule called a BASE .
-Sometimes referred to as nitrogenous ses as they contain NITROGEN .

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5
Q

What is attached to the other side of the sugar molecule ?

A

We find a negatively charged phosphate group .
-meaning nucleotides contain the elements carbon , hydrogen, nitrogen and phosphorous .

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6
Q

represent nucleotides using a simpalr model

A

-need to learn this structure , so check the sheet

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7
Q

-nucleotides are used to make both the molecules DNa +RNA

A

-The nucleotids in DNA + RNA all share the same general structure.
-But tere is specific differences

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8
Q

First difference between DNA + RNA

A

-In DNA , the pentose sugar is clled deoxyribose .
-Whereas in RNA , the pentose sugar is called ribose .
-Deoxyribose has one fewer oxygen atoms than ribose .

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9
Q

second difference between DNA + RNA

A

(check sheet )
-In DNA nucleotides , we find four different bases
-If you look at the bases you will see two have a DOUBLE RING strucutre . Adenine +guanine
-Scienists call these PURINES .

-The other two bases - thymine nd cytosine have a single ring strucutre
-scienitsts call these pyrimidines .

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10
Q

Third difference between DNA and RNA

A

Just like DNA , RNA also contains denine guanine and cytosine .
-Howeveer , RNA DOES NOT containthymine .
-Instead it contains URACIL .
NEED TO KNOW THIS AS THIS IS VERY IMPROTANT .

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11
Q

General strucutre of a nucleotide (check sheet)

A

-Can see the hydroxyl group on carbon 3 of the pentose sugar.
-That is because it plays a really important role.

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12
Q

What is the important role ?

A

-If we take two nucleotides (check next page )
-Then we cn form a ond between them -PHOSPHATE GROUP of one nuecleoitde + hydorcyl group onc arbon 3 of the pentose sugar on the othe rnucleotide ,
(check sheet to see bond )

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13
Q

What is the bond called ?

A

PHOSPHODIESTER BOND - NEED TO KNOW THIS !!!!!!!!

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14
Q

-wHAT HAPPENS WHEN THE PHOSPHODIESTER BOND IS FORMED ?

A

-Water is released so is an example of a condensation reaction .
-+THIS moelcule we formed is a dinucleotide .
-can break the phosphoidester ond by adding water .
-THIS IS A hydrolysis reaction

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15
Q

-We can continue to add nucleotides by forming phosphodiester bonds .

A

Have formed a polymer of nucleotides and scientists call is a polynucleotide BOTH DNA RNA are examples of polynucleotide.

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16
Q

Structure of dna

A

Dna consists of two polynucleotide stands .
-we have the sugar phosphate backbone on the outside with bases on the center .
-the two poly ue Lodi fox’s stands are held together by hydrogen bonds , which form between the bases on opposite strands .

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17
Q

KEY : based on one strand are complementary to the bases on the other strand .

A

Guanine on one strand always pairs with cytosine on the opposite strand . Adensine slways pairs with thymine .

-this complementary base pairing is central to how Dna functions .

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18
Q

In the last video , we saw both adenine and guanine are purines because of their DOUBLE RING structure .

A

iWhereas thymine and cytosine are pyrimidines because they have a single ring .
-what this means is that purine on one strand always pairs with pyrimidine on the oppsoite strand .

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19
Q

This means that the distance between the sugar phosphate backbone is constant , all down the DNA molecule.

A

-the two polynucleotide strands in Dna are anti parallel . Meaning they run in opposite directions .

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20
Q

-looking at the left hand side , we can see that the top of the phosphate group is attached to carbon 5 of the deoxyribose sugar .

A

At the bottom , we have the carbon 3 hydroxyl at the top .
At the bottom , we have the carbon 5 attached to the phosphate.

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21
Q

The different base pairs form a different number of hydrogen bonds .

A

Adensine and cytosine form three hydrogen bonds , whereas Adenine and thymine form two hydrogen bonds .

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22
Q

Because of the complementary base pairing , the properties of guanine and cytosine are always the same as eachother .

A

The proportions of Adensine and thymine are also the same as eachotehr .
-this means we can calculate the proportions of the different nucleotide

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23
Q

Check sheet for example question

A

…

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24
Q

The two polynucleotide strands in dna , twist around eachother and form a double helix

A

We can see that the sugar phosphate backbones on the outside and base pairs in the center .

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25
Q

Structure of rna
RNA is also a polynucleotide but rna is different in a number of ways :

A

RECAP :
RNA contains the Penrose sugar ribose rather than the deoxyribose found in DNA .
RNA does not contain the base thymine , instead , RNA has the base uracil .

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26
Q

One difference between DNA and RNA

A

Dna is found in chromosomes of the nucleus whereas RNA is found in the cytoplasm .
RNA plays a key role in protein synthesis .

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27
Q

Second difference between DNA and RNa

A

DNA is an extremely long molecule .
-Often containing many millions of nucleotides .
-in contrast , RNA molecules are much shorter , making RNA molecules only contain a few hundred nucleotides

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28
Q

Third diffeeence between DNA and RNA

A

Lastly , Dna is a double stranded molecule , consisting of two polynucleotide starts twisted into a double helix .
Whereas rna molecules consist of only one polynucleotide strand .

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29
Q

Dna replication -everytime a cell undergoes divison , all of the DNA is copied .

A

The process is called DNA replication .

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30
Q

Stage one of DNA replication

A

The enzyme DNA helicase attached to the DNA molecule .
-DNA helicase causes the hydrogen bonds between the complementary bases to break .

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31
Q

Stage two of dna replication

A

This causes the two polynucleotide strands to separate from each other .

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32
Q

Stage theee of dna replication

A

Now , free nucleotides line up with their complementary bases on the DNA strands .
At this stage , the free nucleotides are only held in place by HYDROGEN BONS between the complementary bases .
-they are not bonded to eachother by phosphodiester bonds .

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33
Q

Notice something different about free nucleotides ?

A

Thee are called activated nucleotides .
-SHEIN a normal activated nucleotide inactivated nucleotide has three phosphate groups . Where a normal nucleotide contains

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34
Q

Going to the previous diagram , as you can see activated nucleotides are lined up , held in place by hydrogen bonds between the complementary base pairs .

A

…

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35
Q

Stage four of dna replication

A

At this stage , a second enzyme kow attached . Enzyme is called DNA polymerase .
DNA polymerase or down the molecule and catalyses the formation between the formation of a phosphodiester bond between the activated nueclpetodes . This is an example of a condensation reaction .

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36
Q

Key : when phosphodiester bonds forms , the activated nucleotides lose , their extra two phosphate groups .

A

As those two phosphate groups leave this provides energy for the reaction .

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37
Q

Now got , two copies of our four double standard molecule .

A

However , each of the DNA molecules contain one strand from the original DNA molecule and one stand which is brand new .

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38
Q

-this type of Dna replication is called semi consecrate replication

A

Important dna is coped accurately

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39
Q

But sometimes , an incorrect bade is inserted into the growing polynucleotide strand

A

This means that the sequence has changed .
Scientists cal this mutation and these can be very harmful to the organisms .

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40
Q

Remember , mutations wre random and occur spontaneously

A

Heck fhe video girl it’s so illegible

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41
Q

What happens in semi conservative replication

A

In semi conservative replication , the Dna helix sepearate into two polynuecleotide strands .
-Each strand is then replicaed into a complementary NEW STRAND .

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42
Q

-SSo at the end ONE molecule of DNA has been copeid into two m olecules of DNA .
KEY about semi conservatie replication

A

Two copies contain one strand fromt he original DNA moleucle and one enw strand ( orginal is in white and new one is in red in the picture )

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43
Q

-When the strucuture of DNA , was discovered int he 19501s , scienitsts did not KNOW how dna is replicaed .
-Semiconservative replication was ONE possilit .

A

-Another possiilitt was CONSERVATIVE REPLCITION ; a DNA double helix i formed contaning TWO NEW STRANDS .
-The DNA moelcule contains none of the ORIGINAL DNA .
-SO scienistss had ot design an EXPERIEMNT .

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44
Q

so scienitsts had to design an experiemnt to show whether DNA replcited by cosnervaive or semi conservative repliciton .

A

….

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45
Q

experimentnal details and results .

A

-to udnerstand this experment , need to understand ONE IDEA .
-All of the bases of DNA CONTAIN THE ELEMENT NITORGEN .

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46
Q

Nitrogen exists as two main isotopes , what are they ?

A

Nitrogen -14+Nitorgen -15 .
-Nitrigen -14 is the most common isotope , With over 99% of nitrogen atoms being nitrogen-14 .
KEY ; ntirogen-15 is sligghtly HEAVIER than atoms of Nitrogen-14 .

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47
Q

Stage one of the experiment

A

scientists took a sample of BACTERIA .
-Under normal contions , almost all of the nitrogen atoms atoms in the DNA of these bacteria , will be nitrogen-14 (the lighter isotope ) .

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48
Q

stage two of the experiment

A

scieniets now took some of this bacteria and extracted the DNA .

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49
Q

Stage three of the experiment

A

they then placed the DNA in a solution and spun this at a very high speed in a centriguge .

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50
Q

stage four of the epxeriemnt

A

the DNA moved down the solution and formed a band the scientists could detect .

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51
Q

KEY of the experiment

A

thhe postion of the DNA band depends on how heavy the DNA IS .
-Because of the nitorgen atoms int he DNA were almost all nitorgen-14 .(high nitorgen )
-This forms a banf ear the TOP of the tube .

(I have repreented the DNA containing light nitorgen represented as FAINT LINES )

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52
Q

Stage five of the expweriment

A

scientists culture the bcteria in a growth medium .
-Which contains only nitrogen whicho ne .

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53
Q

stage six of the experiment

A

after the bacteria had reproduced many many times .
-Almost all the nitrogen atoms in the DNA was nitogen-15 (heavy nitogen ) .

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54
Q

stage seven of the experiment

A

when this dna was extracted and centriguged .
-it formed a band near the bottom of he tube .
(DNA containing heavy nitrogen represened as THICK LINES ) .

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55
Q

SUMMARISE
-When bacteria are grown in nitorgen -14 what does this mean ?

A

-Because their DNA was LIGHTER it formed a band near the top of the tube .
-But when nitrogen as their dna was HEAVIER it formed a BAND neAr the BOTTOM OF THE TUBE . -

56
Q

STAGE EIGHT OF THE EXperimetn

A

now scienitsts took a sample of the acteri which ahd been growing on nitorgen- (heavy nitrrogen

-scienitsts transferred these bacteria to nitorgen-14 .
-allowed them to replciate their dna oly ocne .

57
Q

stage nine of the experiment

A

the scientists extracted the DN nd spun it in a centriguge .
-What they found out was that this DNA porduced a band inebtween he two bands produced BEFORE
-This told the scienitsts that this DNA containied one strand containing N-14 and one with N-15 .

58
Q

WHY IS this finding really improtant

A

this si really improtnt ,as this means tht the DNA must have replciated SEMICONSERVATIVELY
REMEBER - ina semiconservtive repliction the DNA porduced contains one strand fromt he ORIGINAL DNA and one compeltely new strand .

4-In this case , the replicaated DNA , has one strand containig nitorgen-15 and one strand nitrogen-14.

59
Q

Stage ten of the experiment

A

At this point , the scienitsts allwoed the bacteria one more time of ntirogen-14 .
-Whent eh DNA ws extracted nd spun it produced a band t the BTTOM shown here .
-We still have the INTERMEDIAR BADN but we now have a band enr the TOP pof the tube .

60
Q

We can xplain this if we go ack to pur previosu diagram .
-After the second round of replication , we have four DNA molecules .

A

2 contains one strand of N-14 . and stand with N15 , can see here .
-This represents dgidg
-The two n-1 dna moelcules both contain two strand with oonly n-14 tjese repset the ond .

61
Q

EXAM –> could e sked to suggest what resuts would show if DNA replicte cosnervatively rather thean semi cosnervaively

A

remember , conservative rep ends upw ith one moelcuel df DNA continig wo ignal strans .
-ANd oen meolcule of DNA contianin two new stands .
-back to the experiment after one round replication , we would have one dna moelculecontaining only ntirogen -15 and one moelcule with only ntioreng -14.

62
Q

After two rounds of replciaiton we would sitll only have one moelcule only nitorgen-15 ut 3 dna moelcul continign n-14

A

…

63
Q

key WE HAVE no dna moelcules CONTAINING both n-14+2-15.

A

So with conservative rpelciaiton , we would get to see a bdongin pattern , shown here .

64
Q

-In cells , the DNA is arranged in a speciic way .

A

this is different between eukaryotes and prokaryotes like bacteria .

65
Q

one difference between prokaryotes and eukaryotes .

A

-DNA in prokryotes iss usually circular with no free ends .
HOWEVER ; in euakryotes the DNA mooleucle are linear (got two ines ) .

66
Q

second difference between prokaryotes and eukaryotes .

A

In prokaryotes , the DNA molecule are relatively short and compared ot the FN moelcules in eukryotic cells which re much logner .

67
Q

third difference between eukaryots

A

in eukaryotes , the dn moelcules re tightly wrapped around poteins called HISTONES . Forming compelx strucutres called chromsomes
-In contrast , the DNA in porakryote is not bound to histones .
So prokaryotes DNA does not exist as a chromsomes .
-Have been discussin DNA found int he Nuclleus of eukaryotes .

68
Q

where else can we find dna apart from the nueclues of eukarutes ?

A

-in mtochodnira and chloroplasts .
-This DNA is very simailr to the DNA found in prokarytoes .
(AKA relatively short circulr and not attached to histones .

69
Q

nucelus of eukaryotic cells –. the dark material in the nueclue is the DNA bound to histones . (not possile to any dsitict chromsomes ) - WHY ?

A

That is because , at this stage , the chromsomes have a relativley ioen strucutre .
-At this point , we refer to thDNA and histones a CHROMOATIN.

70
Q

Before a cell divides all of the chormsomoems are copied .
-These two copies remain unattached at point clled the centromere .

A

-Niw the rtwo dna moelcues are called chromatins left chromtin and right chroamtin .
(now refer to whole strucure as chromosmoes .

71
Q

the chromsomes CONDESNE (KA Dna and hsitones form densel packed loops and coilks

A

and chromsomes become visile .

72
Q

Homologous chromsomosomes

A

23 from mother
and 23 from tather
-scienists refer to thesr a homogous oaur
jey 2 chromsomes in a homogous pair have the same genses .

-The postion of a gene ona c hromsome is called ALOCUS for tha gene .

73
Q

WHta is a gene ?

A

gene is a section of DNA , hich encodes the amino acid sequece of a polypetide .

-Soemtimes , random mtuatins tak eplace and this eans cjamhed on ense can occur .
different versiosn .
-Scienitsts call thiese versions of a gene ALLELES .

74
Q

A humans inherits one of each of the homogous chromosmes in a pir one from mother and oen from fther .

A

meaning in a homogus pair , of chromosoems , alleles do not have ot be the same
could e aa bb ab ba .

75
Q
A
75
Q
A
75
Q
A
76
Q

KEY l a lot of the DNA WE FIND INA CHromsomse , do not code for polypetides , WHat are the reasons for this .

A

ONE REASON FOR THIS L i that beween the genes , we find larf amounts of amino acids of repeging base sequeneces .
-THese repeating sequenec sequeneces do ot code .

SECOND REASEON - even twithin the funcionl genses ,w e ind strethe of non-coding DNA , these are called introns .

77
Q

Certaub reguibs if chromsoomes re called GENES

A

…

78
Q

Genes play role in protein ynthesis

A

-as the nuecleotide sequenece of a gene eencodes .
-The primary , strucuture of a polypetide (AKA the sequence of aminoa cids ) .

79
Q

SUMMARY

A

-There are two main stage of protein synthesis the first stage is transcription and this takes in th NUCELUS .

80
Q

SUMMARY- PROTEIN SYNTHESIS

A

-During transcription , they have base sequence of a gene is copied onto a complementary base sequence of a molecule called messenger RNA (mRNA )

81
Q

SUMMARY of protein syntheiss (2)

A

the MRNA molecule then ma moves to the cytoplasm .

82
Q

SUMMARY of PORTEIN SYNTHESIS (3)

A

in the cytoplasm , the ifnormation encoded int he neucleotide seqeucne of the MRNA is used to join a specific order of aminoa cids , formign the polynucleotide . (scienitsts call this trnslation ) .

82
Q

TRANSLATION (1)

A

Part of a gene encoding a specific polypetide .
-Stage one of transcription , DNA helicase breaks the hydorgen bonds becaus eof the stwo strmds.

83
Q

TRANSLATION (2)

A

Now the complementary RNA nucleotides move into place and form hydrogen bonds witht hw bases ont he expodes nuecloeitfrs on one of the DNAstrands .

84
Q

Translation (3)

A

A t this point , the enzyme RNA polymerase joins the RNAnucleotides by forming phosphodiester bons /

84
Q

TRANSLATIOn (4)

A

The enzymes continue to move thier way long the DNA , until they each the end of the gene .

85
Q

translation (5)

A

now the produced stand of messenger RNA .
KEY ; if you looka t he messenegr RNA , you will see that the base sequence is the same as the top of the DNA STRAND .
-EXCEPT thymine has been replaced byu racidl .

86
Q

-we call ths DNA strand the sense strands

A

the Mrna is complementrary to the other DNA strand + we call this the antisense tempalte strand .

87
Q

translatino (6)

A

once the mrna has been syntehsised ,the RNA polymerase deaches from th DNA .
+The DNA foe back to tis normall oduble helix .

88
Q

translation (7)

A

At this sgtgae of the MRNA , moes out og he nuecues htorugh a nueclear por . Onc eint he cytoplams , mRNA CAN TAKE PART INTRANSLATION (MRNA SHORTER THAN IT REALLY IS INRL ) .

88
Q

human hve 23 chromosmes , other orgnisms have more or less .

A

-All the genes in a cell is called GENOME .

-In eukaryotoes , this include both the genes on the chromosomes and the genes in mitochondira and in chloroplasts .

89
Q

-As we’ve seen , the nuecleotide nucleotide sequence of a gene , determines the AMINO ACID seencw od POLYPEPTIDE / PROTEIN .

A

-All of the porteins produved bythe genome of n orgnism is clled the proteome .
-Only a frction of that gene will be those protiens willbe produced in nay particuaalr cell type .
-Cells can produce different rnge of proteins deoedning on what the cell is doing .

90
Q

Key mRNA nucleotide are read as series of triplets .

A

scienitst call these tripet GENETIC DOE .

91
Q

Key features of genetic code one

A

-MOst amino acids have more than one triplet ,
-e.g iplet .
e.gleaine –> 6 triplets nd a large number of maino acid has four .
-because of this scientusts call the geentic code a DEGENERATE CODE .

92
Q

key features of a geentic code 2

A

-the triplet code is non-overlpping
no base is read more than once .

93
Q

third key feature is genetic code

A

-The genetic code is universal .
-The same tripets encode the same aminoacids , in the vast majoring of orgnisms on planet EARTH .

94
Q

As said before ,t he mRNA nucletoide srethe mRNA nucleotide sequence is used to determine where tp dtart tradnslating the mRNA molecule .

A

-This is called a start triplet .
-The start triplet also ecncodes th amino acid methione .

95
Q

-3 triplets determine where translation stops . These are called STOP TRIPLETS .

A

…

95
Q

What happens in translation ?

A

-in trnalsation the nuecleotide sequence of mRNAENCE OF THE Mth mMRN is used to determined the amino acid sequence of a polypeptide .

96
Q

showing a sketch of the MRNA , each triplet in the mRNA is clled a CODON .

A

KEY ; in order for the mRNA to be read , and another type of RNA is invovled .
-GTThis is clled rna (tRNA)
-transfer RNA has two important parts .

97
Q

Imporrtant part one of tRNA

A

-t the top of the TRNA moleucle we have the bidning site for an amino acid .

98
Q

Important part of tRNA two is

A

-at the bottom we have triplet of bases called the anticodon .

99
Q

-The tRNA for the aminoacid methione .

A

-KEY ; the Trna anticodon is complementary to the mRN codon for that amino acid .

100
Q

-go back to our mRNA , one codon is AUG , this is the start CODON , but also the codon for methione .

A

-As you can see the , anticodon , ont he tRNA carrying mehtuoine .
–It is compleentarty to the mRNA codon , for methione and infct this is a complementay TRNA for the codons encoding every amino aicds .

101
Q

REMEMBER ; man amino acids , re encoded bys everal triplet and each of these will have a corresponding transfer RNA .

A

…

102
Q

Stage one of translation

A

-Once the MRNA moves from the neuclues to the cytoplas , the small subunits of a ribosome , binds iwth he mRNA at the start codon .
-Ribosomes contain a number of different porteins . They also contin a type of RN called IBSOOMAL RNA .

103
Q

Stage two of translations .

A

-Now the tRNA moecule with an anticodon , complementary to the start codon attached .
-This is held in place by HYDROGEN BODS between the complementry base pairs in the mRNA nd tRNA .

104
Q

Third stage of transltion

A

-Now a second tRN moelcule moves into place .
-THe ntidcodon on this tRNA is complemenary to the second dondon on the mRNA .
-IN THIS Mrna , THE SECOND CONDON IS CALLED gccg .
-lOOKING AT HE GENETIC CDOE this codnon encodes the amino acid alanine .

105
Q

four stages of translation

A

A peptide bond forms between two amino acids .
-This is catakysed by the enzyme petide ransferase .
-which is actually part of he risomes RNA moeucle .
-+The formation of the peptide bond reruies energy porvided by ATP .

106
Q

Five stage of translation

A

-now the ribosomes move to the next codon nd forms a peptide bodn to the next amino by enzymes int he cytoplasm .

107
Q

six stages of translation

A

-the first rna moleucle is rleeased .
-trna moelcules that have been released re attached to their amino acids by enzymes int he cytoplasm .

108
Q

seven stage trnalsation

A

-the ribodomes continues moving down the mRN forming the polypeptie .

109
Q

stage eight of translation

A

when the ribsoome comes to a stop codon , it detached the polypeptide chain and is rleased .

110
Q

key

A

rleeased .
-I should just point out that one the first ribsoome , has stored another ribsoome can attach to th other stat codona nd start traslating .
-we might see a wole line o ribosomes making htier ay along the mRNA >
-tHIS MEANS that a large of polpeptide moleucles can be produced rapildy .

111
Q

stage nine of translation

A

once the polypeptide chain hs crefully foledeit can then carry out its function in the ce;.

112
Q
A
113
Q
A
113
Q
A
114
Q

Where are covalent bonds formed by consolidation

A

Condensation reactions .

Nitrogenous base is linked with c1 of the sugar residue and phosphate groip linked to either c5 or c3

115
Q

Nucleotides consolidation

A

They become phosphorylase’s nucleotide when they contain more than one phosphide groip

116
Q

Nucleotide part two

A

They help to regulate many metabolic pathways xx

An may be components of many coenzymes

117
Q

Pjosphodester bond is

A

Covalent bond

118
Q

Equal sized rings on the fam ladde

A

Caused by a oriole alwahs pairing worj phrimode

Giving the molecule stability

119
Q

Consolidation semi convergence replocarion

A

Look at page 89 bruh

120
Q

What are the theee forms of rna

A

Messenger rna
Transfer rna tRNA
And ribosomal rna rrna

121
Q

Why is the generic code described as ehe rage

A

As most amino acids fhere is more than one base triplet xx

  • this may reduce the effect of loint mutations as a change in one base of the toilet could produce another base triplet thay codes for the same amino acid
122
Q

What do magnesium ions do for riniodomes

A

Magnesium ions jelly to bond the ribosome subunits togeyher

123
Q

What happens after the polypeptide change has been assembled consolidator

A

The mRNA breaks down and its component loelfilew can be recycled into new lengths of mRNA with different condom sequences. .

124
Q
A
124
Q
A
124
Q
A
124
Q
A
125
Q

Table lists fhe steps involved ind na extraction why is

  • sample blended w a mortar and pestle
  • detergent added
    Protease added
  • ethanol added
A
  • break down cell walls
  • break down fell memebranes
  • break down proteins associated with dna
  • to precipitate the sna

A-level Biology (21 decks)

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