Edexcel SNAB A Level Biology - Topic 2

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What are the monomers of proteins?

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Biology

12th

173 Terms

1

What are the monomers of proteins?

Amino acids

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2

Dipeptide

Two amino acids bonded together

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3

Polypeptide

A polymer (chain) of more than two amino acids bonded together

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4

What are proteins made of?

One or more polypeptides

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5

What is the general structure of amino acids?

A carboxyl group, an amine/amino group, a carbon-containing R group

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6

How many amino acids are there?

20

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7

What is the difference between amino acids?

Their R group

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8

How are amino acids linked?

Condensation reaction

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9

What is released in a condensation reaction?

Water molecule

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10

What type of bond is formed between amino acids?

Peptide bond

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11

What are the 4 structural levels of proteins?

Primary, Secondary, Tertiary, Quaternary

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12

What is the primary structure of a protein?

The sequence of amino acids in the polypeptide chain

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13

What is the secondary structure of a protein?

The 2D arrangement of the chain of amino acids. Alpha helix or Beta pleated sheet

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14

What determines the secondary structure of a protein?

Hydrogen bonds between amino acids

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15

What is the tertiary structure of a protein?

The 3D structure of a protein

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16

What determines the tertiary structure of a protein?

Hydrogen bonds, ionic bonds, disulphide bridges, hydrophobic and hydrophilic interactions

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17

What is the quaternary structure of a protein?

Some proteins are made of more than one polypeptide chains linked together. The quaternary structure is the way these polypeptide chains are assembled together

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18

What is the primary structure of proteins held together by?

Peptide bonds between amino acids

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19

Ionic bonds in proteins

Attractions between negative and positive charges on different parts of the molecule

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20

Disulphide bridge/bond in proteins

Covalent bond between sulphur atoms of two cysteine amino acids

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21

Hydrophobic interactions in proteins

When hydrophobic groups are close together, they tend to clump together

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22

Hydrophilic interactions in proteins

Hydrophilic groups get pushed to the outside

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23

What do hydrophilic/phobic interactions affect tertiary structure?

They affect how the protein folds up

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24

How does a proteins primary structure determine its 3D structure and properties

The amino acid sequence of a protein determines what bonds will form and how the protein folds into its 3D structure. The 3D structure determines its properties and function in the body

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Globular proteins

  • Round, compact proteins made up of multiple polypeptide chains.

  • Complex tertiary/quaternary structures.

  • Form colloids in water

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How are the chains structured in globular proteins?

Coiled up so that hydrophilic parts are on the outside and hydrophobic parts face inwards

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27

What are the two types of protein 3D structure?

Globular Fibrous

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28

How does the structure of globular proteins make it good for their function?

Makes them soluble, so they're easily transported in fluids

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Hydrogen bonds

Weak bonds between a slightly positively charged hydrogen atom in one molecule and a slightly negatively charged atom in another molecule

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Example of globular protein

Haemoglobin

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Haemoglobin strucutre

Globular protein made of 4 polypeptide chains. It has iron-contains haem groups that bind to oxygen

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What is the function of haemoglobin?

Carries oxygen around the body

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How is haemoglobin suited for its function?

Its soluble so can easily be transported in the blood

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Collagen structure

Fibrous protein made up of 3 polypeptides

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Fibrous proteins

  • Long, insoluble polypeptide chains, tightly coiled round each other to form a rope shape

  • Chains are held together by lots of bonds, making the proteins strong

  • Little tertiary/quaternary structure

  • Occasional cross linkages which forms microfibres for tensile strength

  • Insoluble

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How are fibrous proteins suited for their function?

They are strong so are often found in supportive tissue

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37

How is collagen suited for its function?

High tensile strength due to hydrogen and covalent bonds and forms the structure of bones, cartilage and connective tissue in animals

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38

What do enzymes do?

Catalyse metabolic reactions

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39

Intracellular enzymes

Catalyse reactions inside the cell

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40

Extracellular enzymes

Secreted by cells to catalyse reactions outside of cells

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41

Are enzymes proteins?

Yes

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42

Activate site of enzymes

Has a specific shape where the substrate molecules bind to

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43

What makes enzymes specific?

Their tertiary structure

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44

How do enzymes catalyse reactions?

They lower the activation energy needed for a reaction

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45

Enzyme-substrate complex

A complex formed when an enzyme binds to its substrate molecule(s).

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Activation energy

Energy needed to get a reaction started

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47

How does an enzyme substrate complex lower activation energy?

  • If 2 substrate molecules need to be joined, being attached to the enzyme holds them close together, reducing and repulsion between the molecules so they can bond more easily

  • In a breakdown reaction, fitting into the active site puts a strain on the bonds in the substrate so the molecule breaks up more easily

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Induced fit model

Change in the shape of an enzyme's active site that enhances the fit between the active site and its substrate(s)

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49

How do enzyme properties relate to their tertiary structure?

  • Enzymes are very specific and usually only catalyse one reaction because only one complementary substrate will fit into the active site

  • The enzyme's active site is determined by it's tertiary structure

  • Each enzyme has a different tertiary structure and so a different shaped active site

  • If the substrate doesn't match the active sit, the enzyme-substrate complex won't be formed and the reaction won't be catalysed

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50

What can the tertiary structure of an enzyme be altered by?

Changes in pH or temperature

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51

What is the primary structure of a protein determined by?

The sequence of nucleotides in the gene encoding for amino acids

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52

How does enzyme concentration affect enzyme activity?

The more enzyme molecules there are in a solution, the more active sites present and the more likely a substrate molecule is to collide with an active site and form an enzyme-substrate complex

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53

What is the limiting factor in enzyme catalysed reactions?

Substrate concentration

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54

What does DNA stand for?

Deoxyribosenucleic Acid

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55

What does RNA stand for?

Ribonucleic acid

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What are mono nucleotides made from?

  • Pentose sugar

  • Nitrogen-containing organic base

  • Phosphate group

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Pentose sugar

Sugar with 5 carbon atoms

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58

DNA and RNA are polymers of what?

Mononucleotides

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59

What is the pentose sugar in a DNA mononucleotide called?

Deoxyribose

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60

Each DNA mononucleotide has the same _____ and a ____/

  • Sugar

  • Phosphate group

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What varies between DNA/RNA mononucleotides?

Their base

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4 bases (DNA)

  • Adenine (A)

  • Thymine (T)

  • Cytosine (C)

  • Guanine (G)

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What is the pentose sugar in a RNA mononucleotide called?

Ribose

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64

Each RNA mononucleotide has the same _____ and a ____/

  • Sugar

  • Phosphate group

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4 bases (RNA)

  • Adenine (A)

  • Uracial (U)

  • Cytosine (C)

  • Guanine (G)

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Polynucleotide

A polymer consisting of many mononucleotide monomers in a chain

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What are polynucleotides joined by?

Condensation reaction between the phosphate of one mononucleotide and the sugar group of another

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How many polynucleotide strands is DNA made up of?

Two

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69

How many polynucleotide strands is RNA made up of?

One

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70

How do two DNA polynucleotide strands join together?

Hydrogen bonding between bases

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71

What are the DNA base pairs?

Adenine - Thymine (A-T)

Cytosine - Guanine (C-G)

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Complementary base pairing

Hydrogen bonding between particular pyrimidines and purines

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Pyrimidines

  • Cytosine

  • Thymine

  • Uracil

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Purines

  • Adenine

  • Guanine

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How many hydrogen bonds form between A and T?

Two

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How many hydrogen bonds form between C and G

Three

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77

DNA double helix

Two antiparallel polynucleotide strands twist to form the DNA double-helix

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78

Who and when determined the double-helix structure of DNA

Watson and Crick - 1953

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79

Gene

Sequence of mononucleotide bases on a DNA molecule that codes for the sequence of amino acids in a polypeptide

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80

Different proteins have a different ______ and _____ or amino acids

  • Number

  • Order

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81

How many bases code for one amino acid?

Three

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82

Does DNA move out of the nucleus?

No, It is too large so is copied into mRNA (transcription). The mRNA leaves the nucleus and joins with a ribosome in the cytoplasm, where it can be used to synthesise a protein (translation)

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83

Two types of RNA

  • Messenger RNA (mRNA)

  • Transfer RNA (tRNA)

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84

When and where is mRNA made?

In the nucleus during transcription

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What does mRNA do?

Carries the genetic code from the DNA to a ribosome in the cytoplasm, where it's used to make a protein during translation

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86

Codon

A specific sequence of three adjacent bases on a strand of DNA or RNA that provides genetic code information for a particular amino acid

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87

Where is tRNA found?

The cytoplasm

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What does tRNA have at each end?

Amino acid binding site at one end and an anticodon at the other end

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Anticodon

A sequence of three bases of a tRNA molecule that pairs with the complementary three-nucleotide codon of an mRNA molecule during protein synthesis.

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90

What does tRNA do?

Carries the amino acids that are used to make proteins, to the ribosomes during translation

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91

What are codons and anticodons sometimes referred to as?

Triplets

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92

Genetic code

The sequence of base triplets (codons) in DNA or mRNA which codes for specific amino acids

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Features of genetic codes

  • Degenerate (more than one genetic code corresponds to one amino acid)

  • Non-overlapping (base triplets don't share their bases, each is separate from the triplet before)

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How many possible triplets are there?

64

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Start and Stop codons

Triplets used to tell the cell when to start and stop the production of the protein. Found at the beginning and end of the gene

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96

What is the first stage of protein synthesis called?

Transcription

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Stage 1 of transcription:

Transcription starts when RNA polymerase attaches to the DNA double-helix at the beginning of a gene (start codon)

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98

Transcription starts when RNA polymerase attaches to the DNA double-helix at the beginning of a gene (start codon)...

Stage 2 of transcription:

The hydrogen bonds between the two DNA strands in the gene break, separating the stands and causing the DNA molecule to unwind.

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99

The hydrogen bonds between the two DNA strands in the gene break, separating the stands and causing the DNA molecule to unwind...

Stage 3 of transcription:

One of the strands is used as a template to make an mRNA copy

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One of the strands is used as a template to make an mRNA copy...

Stage 4 of transcription:

RNA polymerase lines up free RNA mononucleotides alongside the template strand. Complementary base pairing means the mRNA ends up being a complementary copy of the DNA strand (with T being replaced with U)

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