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OCR AS-level Biology > 2.1.3 nucleotides & nucleic acids > Flashcards

2.1.3 nucleotides & nucleic acids Flashcards

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1
Q

What do nucleic acids contain

A

Carbon, hydrogen, oxygen, nitrogen and phosphorus

C H O N P

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2
Q

What is a nucleotide structure

A

they contain a pentose (5 carbon) sugar, phosphate group, nitrogenous base

The pentose sugar connect to the phosphate by a phosphodiester bond and the sugar connects to the nitrogenous base by a glycosidic bond

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3
Q

What are the four bases

A

purines: adenine and guanine ( A G)

Pyrimidines: thymine and cytosine ( T C)

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4
Q

Name the pentose sugars in DNA and RNA

A

DNA: deoxyribose

RNA: ribose

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5
Q

What are the anti-parallel sides

A

The 5’ end is where a phosphate is attached to carbon 5.

The 3’ and is where a hydroxyl group is attached to carbon 3

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6
Q

What is complimentary base pairing

A

Purines always pair with pyrimidines

Adenine joins with thymine & forms 2 hydrogen bonds

Cytosine joins with guanine and forms 3 hydrogen bonds

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7
Q

what is the job of the helicase enzymes

A

Unzips the two strands breaking the hydrogen bond

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8
Q

What name is given to the short strand of RNA or DNA that serves as a starting point for DNA synthesis

A

prima

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9
Q

Where is DNA found

A

DNA is found as a strand in bacteria. In eukaryotic cells it is found in the mitochondria, chloroplast and nucleus Strand in viruses

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10
Q

Where does DNA replication occur

A

It occurs in the nucleus of eukaryotic cells

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11
Q

When does DNA replication occur

A

It happens during interphase when a cell is growing, carrying out cell processes and replicating its DNA

DNA replication does not occur during cell division in mitosis all meiosis it occurs before

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12
Q

what does helicase do

A

Unzips the enzyme. Unzips the double helix strand of DNA

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13
Q

what does DNA polymerase do

A

Replicates DNA molecules to build a new strand of DNA

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14
Q

what does ligase do

A

glues DNA fragments together

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15
Q

what does primase do

A

Primers makes primers To indicate where DNA polymerase should go to perform its function

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16
Q

Describe DNA replication

A

it is semi Conservative. This is where DNA replication results in one old strand and one new strand present in each daughter DNA molecule

gyrase uncoils
helicase unzips and breaks hydrogen bonds
polymerase creates the phosphodiester bond
two strands of DNA are separated by the enzyme dna helicase
Each strand acts as a template for the formation of a new strand

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17
Q

Describe how polynucleotide strands are formed and broken down

A

condensation reactions between nucleotides form strong phosphodiester bonds (sugar-phosphate backbone). Hydrolysis reactions use a molecule of water to break these bonds. Enzymes catalyse these reactions

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18
Q

Describe the structure of DNA

A

molecule twists to form double helix of two deoxyribose polynucleotide strands, so there are two sugar phosphate backbones

Hydrogen bonds form between complimentary base pairs on strands that run antiparallel

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19
Q

Why is DNA replication described as semiconservative

A

strands from original DNA molecule act as templates. new dna molecule contains one old Strand and one new strand. Specific base pairing enables genetic material to be conserved accurately

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20
Q

explain the role of DNA helicase In semiconservative replication

A

It breaks hydrogen bonds between base pairs to form two single strands, each of which can act as a template

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21
Q

How is the new strand formed during semiconservative replication

A

Three nucleotides attach to exposed bases by complimentary base pairing

DNA polymerase joins adjacent nucleotides on new strand in a 5’ -> 3k’ Direction via condensation reactions to form phosphodiester bonds

Hydrogen bonds reform

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22
Q

Describe discontinuous and continuous replication

A

continuous: One strand is replicated in a continuous strand
discontinuous: formed by ozaki fragments being made as the dna unzips which then join together with ligase

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23
Q

How many amino acids make up the proteins in an organism

A

20 amino acids And the order of amino acids determines the protein

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24
Q

How many bases code for one amino acid

A

Three, this is known as a triplet/codon

25
Q

define degenerate (feature of the genetic code)

A

more than one triplet code for the same amino acid (64 possible triplets for 20 amino acids )

The leftover triplets mean that there are some amino acids which have more than one triplet as there are 20 amino acids and 64 different possible codons

26
Q

define non-overlapping (feature of the genetic code)

A

each triplet is only read once

Having a single code on that starts the sequence insures that there is no overlap. This means that the DNA sequence will always be read from the first base and not the second or third

27
Q

define universal (feature of the genetic code)

A

same bases and sequences used by all species

The same triplet of DNA bases codes for the same amino acid regardless of the organism

28
Q

Describe how DNA can be purified by precipitation

A

Add ethanol and a salt to aqueous solution. Nucleic acids precipitate out of solution. Centrifuge to obtain pallet of nucleic acid. Wash pellet with ethanol and centrifuge again

29
Q

What does transcription produce and where does it occur

A

it produces mRNA

Occurs in nucleus

30
Q

Outline the process of transcription

A

1 RNA polymerase binds to promoter region on a gene

2 section of DNA un coils into two strands with exposed bases. antisense strand acts as a template

3 free nucleotides are attracted to their complimentary bases

4 RNA polymerase Joins adjacent nucleotides to form phosphodiester bonds

31
Q

what happens after a strand of mRNA Is transcribed

A

RNA polymerase detaches at terminator region

hydrogen bonds reform and DNA rewinds

splicing removed introns from pre- mRNA in eukaryotic cells

mRNA Moves out of nucleus via nuclear pore and attaches to ribosome

32
Q

What does translation produce and where does it occur

A

it produces proteins

occurs in cytoplasm on ribosomes which are made of protein and rRNA

33
Q

Outline the process of translation

A
  1. ribosome moves along mRNA until ‘start’ codon

2 tRNA anti codon attaches to complimentary bases on mRNA

3 condensation reactions between amino acids on tRNA Form peptide bonds. This requires energy from ATP hydrolysis

4 process continues to form polypeptide chain until ‘stop’ codon is reached

34
Q

Describe the synthesis of a polypeptide (translation)

A

the tRNA Molecule brings a specific amino acid to the ribosome

The anti codon on the tRNA binds temporarily to the code and on the mRNA

two tRNA Molecules are adjacent to each other in the ribosome

The ribosome forms a peptide bond

The amino acid dissociates (breaks off) from tRNA , So you are left with tRNA Molecule without an amino acid

The now empty tRNA
Goes back into the cytoplasm and joins with another specific amino acid

35
Q

describe the structure of ATP (adenosine triphosphate) and ADP (adenosine diphosphate)

A

Nucleotide derivative of adenine

ATP has 3 inorganic phosphate groups

ADP has 2

36
Q

What is a mutation

A

an alteration to the DNA base sequence. Mutations often arise spontaneously during DNA replication

37
Q

Describe the properties of ATP

A

small: moves easily into, out of and within cells

water-soluble: energy requiring processes happen in aqueous environments

releases energy in small quantities: quantities are suitable to most cellular needs, so that energy is not wasted as heat

Easily re-generated: can be recharged with energy

38
Q

What are the differences between DNA and RNA in terms of their nucleotide bases

A

DNA: for nitrogenous bases-A, G, T, C

RNA: nitrogenous base URACIL Which is a pyrimidine replaces the pyrimidine base THYMINE

39
Q

What are the differences between DNA and RNA in terms of the number of polynucleotide strands

A

DNA: two antiparallel strands as they run in opposite directions

RNA: single-stranded and much shorter

40
Q

Where is RNA located in eukaryotic cells

A

Cytoplasm

41
Q

During which physiological process is ATP, which is needed for protein synthesis, made in cells

A

Cellular respiration

42
Q

ppq: which of these statements about DNA replication is incorrect

The DNA molecule unwinds
hydrogen bonds between the base pairs break
free RNA Nucleotides join to bases on the exposed DNA strands
both polypeptide strands act as a template
hydrogen bonds form between complimentary bases
three hydrogen bonds form between bases a & t
DNA polymerase links the new nucleotides
covalent bonds form between the phosphate of one nucleotide and the pentose sugar of the next nucleotide

A

incorrect:

free RNA Nucleotides join to bases on the exposed DNA strands

both polypeptide strands act as a template

3 hydrogen bonds form between bases a and T

43
Q

ppq: State the number of DNA nucleotide bases that code for a single amino acid

A

3

44
Q

ppq: there is a maximum of 64 different based combinations in DNA that could each code for an amino acid

How is this number of combinations calculated

A

4 X 4 x 4

4 to the power of 3

45
Q

ppq: 20 different amino acids are commonly used for protein synthesis. In theory, this would need only 20 different base combinations. Explain the uses of the 44 remaining combinations

A

several triplets code for one amino acid. Some are used as start/stop/termination. And mutation may not result in a change in amino acid

47
Q

ppq: Describe how a nucleotide by sequence in a gene is used to synthesise a polypeptide

A

transcription: DNA is copied/transcribed into mRNA. three nucleotides line up by complimentary base pairing to one template of the DNA strand catalysed by RNA polymerase
translation: mRNA Moves to ribosomes, tRNA Molecules bind to mRNA. anti codons match and bind to codons. specific amino acid attached to tRNA, Formation of peptide bond between amino acids

48
Q

ppq: complete the following paragraph by using the most appropriate terms

a gene is a section of____that codes for the production of a ____

The molecule that copies a gene and carries the information to a ____ is called RNA

A

A gene is a section of DNA that codes for the production of a POLYPEPTIDE (also accept protein)

The molecule that copies a gene and carries the information to a RIBOSOME is called RNA

49
Q

ppq: deoxyribose is a pentose sugar that is a component of the double-stranded DNA molecule. Describe the structural relationship between deoxyribose and the other components of the DNA molecule

A

part of nucleotide, bonded to base and phosphate. Phosphate joined to C5 and C3. Deoxyribose is part of the backbone of DNA and links with the second phosphate on adjacent nucleotide. Nucleotide is the monomer of DNA and DNA is formed from a chain of nucleotides

50
Q

ppq: Describe how the DNA molecule replicates

A

semiconservative replication: double helix un coils. Hydrogen bonds between the bases break. Each strand acts as the template for the formation of a new molecule. Free nucleotides align with exposed bases. Complimentary base pairing and hydrogen bonds reform. Sugar phosphate backbone forms DNA polymerases joins and each new molecule has one old and one new strand

51
Q

ppq: complete the following statement

A sequence of DNA nucleotides that codes for a protein is a ____

A

gene

52
Q

ppq: Suggest why DNA is not able to leave the nucleus

A

it is too big to fit through the pore in nuclear envelope

53
Q

ppq: explain why the mRNA Molecule is shorter than a DNA molecule

A

mRNA Only codes for one protein whereas DNA Codes for many proteins

54
Q

ppq: State the components of a DNA nucleotide

A

deoxyribose sugar, phosphate group and nitrogenous bases eg a t c g

55
Q

ppq: Suggest how changing the sequence of DNA nucleotides could affect the final product the DNA codes for

A

Different sequence of amino acids means that different proteins fold up differently and therefore the product can no longer function e.g. active site of an enzyme no longer complimentary to substrate

56
Q

ppq: Explain how the structure of DNA allows replication

A

Double-stranded: both strands act as template. Hydrogen bonds easily break between bases. Complimentary base pairing: Purines only able to bind to pyrimidines due to different sizes and three hydrogen bonds between C and G and two hydrogen bonds between a and T

57
Q

ppq: Complete the following passage

DNA is found in the nucleus. The molecule is twisted into a ___ in which each of the strands are ___. it has two ____ backbones attached to one another by complimentary bases. These bases pair in the centre of the molecule by means of ____ bonds

A

double helix

anti parallel

sugar phosphate

Hydrogen

58
Q

ppq: state the role of mRNA

A

Carries the genetic information out of the nucleus and transfers it to the ribosome for protein synthesis

59
Q

ppq: Explain why complimentary base pairing is important in DNA replication

A

DNA can be Replicated without error, reduces occurrence of mutation and allows the formation of hydrogen bonds

OCR AS-level Biology (12 decks)

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