Biological Molecules

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Notas de aula

Chemical Elements in Living Organisms

Most biological molecules are organic, meaning they contain carbon.
The three main groups of organic molecules are carbohydrates, proteins, and lipids.
Carbohydrates contain carbon, hydrogen, and oxygen only.
Proteins contain carbon, hydrogen, oxygen, and nitrogen (some also contain sulfur).
Fats (lipids) contain carbon, hydrogen, and oxygen only.

Carbohydrates

Carbohydrates are made of simple sugars (monosaccharides) like glucose.
Two glucose molecules join to form maltose (a disaccharide).
Many glucose molecules join to form starch, glycogen, or cellulose (polysaccharides).
Starch is the storage carbohydrate in plants; glycogen is the storage carbohydrate in animals.
Cellulose is a structural polysaccharide used in plant cell walls.

Fats (Lipids)

Most fats are triglycerides: one glycerol molecule bonded to three fatty acid chains.
Fatty acids vary in size and structure.
Fats are solid at room temperature; oils are liquid at room temperature.

Structure of a triglyceride: one glycerol molecule bonded to three fatty acid chains.

Proteins

Proteins are long chains of amino acids.
There are about 20 different amino acids found in living organisms.
All amino acids have the same basic structure but differ in their R group.
The order of amino acids determines the protein's structure and function.
Even a small change in the amino acid sequence can produce a different protein.

General structure of an amino acid: central carbon bonded to an amino group, carboxyl group, hydrogen, and an R group.

Food Tests

Benedict's test for reducing sugars: add Benedict's solution, heat at 80°C for 5 min; positive: blue → orange/brick red.
Iodine test for starch: add iodine solution; positive: orange-brown → blue-black.
Biuret test for protein: add Biuret solution; positive: blue → violet/purple.
Ethanol emulsion test for lipids: shake sample with ethanol, then add cold water; positive: cloudy emulsion forms.
DCPIP test for vitamin C: add DCPIP solution to sample; positive: blue colour disappears (becomes colourless).

Benedict's test for reducing sugars: apparatus and colour change on heating.

DNA Structure (Extended)

DNA is a double helix of two strands wound around each other.
The monomer of DNA is a nucleotide, consisting of a phosphate, deoxyribose sugar, and a base.
There are four bases: Adenine (A), Thymine (T), Cytosine (C), and Guanine (G).
Base pairing: A pairs with T, C pairs with G (held by hydrogen bonds).
The sugar–phosphate backbone is on the outside; the bases form the rungs of the ladder.
The sequence of bases codes for the formation of proteins.

DNA double helix showing complementary base pairs (A-T, C-G) joined by hydrogen bonds.

Slides

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CADASTRE-SE — GRÁTIS ENTRAR

Questões de prática

Prévia grátis — 8 de 40 perguntas. Cadastre-se para ver todas.

1.Which of the following is a monosaccharide?
Easy
- AGlucose
- BMaltose
- CStarch
- DGlycogen
2.What are the chemical elements present in all carbohydrates?
Easy
- ACarbon, hydrogen and oxygen
- BCarbon, hydrogen, oxygen and nitrogen
- CCarbon, hydrogen, oxygen, nitrogen and sulfur
- DCarbon, hydrogen and nitrogen
3.Which food test gives a colour change from blue to violet/purple for a positive result?
Easy
- ABiuret test
- BBenedict's test
- CIodine test
- DEmulsion test
4.What is the basic unit of a fat molecule?
Easy
- AOne glycerol and three fatty acids
- BOne glycerol and one fatty acid
- CThree glycerols and one fatty acid
- DAmino acids
5.Which bases pair together in DNA?
Easy
- AA with T and C with G
- BA with C and T with G
- CA with G and C with T
- DA with U and C with G
6.Which of the following is a polysaccharide?
Easy
- ACellulose
- BGlucose
- CMaltose
- DSucrose
7.A food sample gives a blue-black colour with iodine solution. Which substance is present?
Easy
- AStarch
- BGlucose
- CProtein
- DLipid
8.Which of the following elements is found in proteins but not in carbohydrates or lipids?
Easy
- ANitrogen
- BCarbon
- CHydrogen
- DOxygen

Mais perguntas

9.What type of bond holds the two strands of DNA together?
Easy
- AHydrogen bonds
- BPeptide bonds
- CIonic bonds
- DGlycosidic bonds
10.A student adds Benedict's solution to a food sample and heats it. The colour remains blue. What does this indicate?
Easy
- ANo reducing sugar is present
- BStarch is present
- CProtein is present
- DLipid is present
11.If one strand of DNA has the base sequence A C G T, what is the sequence on the complementary strand?
Easy
- AT G C A
- BG C A T
- CA C G T
- DC G T A
12.In the emulsion test for lipids, what is added to the food sample before adding cold water?
Easy
- AEthanol
- BBenedict's solution
- CIodine solution
- DBiuret solution
13.A student tests four food samples with iodine solution and Biuret solution: | Sample | Iodine test | Biuret test | |---|---|---| | A | Blue-black | Blue | | B | Orange-brown | Violet | | C | Blue-black | Violet | | D | Orange-brown | Blue | Which sample contains both protein and starch?
Medium
- ASample A
- BSample B
- CSample C
- DSample D
14.A student adds Benedict's solution to a food sample and heats it. The colour changes from blue to brick red. Which conclusion is correct?
Easy
- AThe sample contains starch.
- BThe sample contains a reducing sugar.
- CThe sample contains protein.
- DThe sample contains lipid.
15.A food sample is tested with DCPIP solution. The blue colour disappears. Which nutrient is present?
Easy
- AStarch
- BReducing sugar
- CProtein
- DVitamin C
16.A triglyceride molecule is composed of one glycerol molecule and three fatty acid chains. What is the ratio of glycerol to fatty acid molecules in a triglyceride?
Easy
- A1:1
- B1:2
- C1:3
- D3:1
17.Which of the following is a disaccharide?
Easy
- AGlucose
- BMaltose
- CStarch
- DGlycogen
18.Which elements are found in all proteins?
Easy
- ACarbon, hydrogen, oxygen
- BCarbon, hydrogen, oxygen, nitrogen
- CCarbon, hydrogen, oxygen, nitrogen, sulfur
- DCarbon, hydrogen, oxygen, nitrogen, phosphorus
19.In the general structure of an amino acid, which part is described as the R group?
Easy
- AThe central carbon atom
- BThe amino group (NH2)
- CThe carboxyl group (COOH)
- DThe variable side chain
20.In a triglyceride molecule, one glycerol molecule is bonded to three fatty acid chains by ester bonds. Which part forms the central backbone of the molecule?
Easy
- AGlycerol
- BFatty acid
- CEster bond
- DPhosphate group
21.A sample of DNA contains 30% adenine. What percentage of guanine is present?
Medium
- A20%
- B30%
- C40%
- D70%
22.A student tests a food sample with iodine solution and observes a blue-black colour. She then tests the same sample with Benedict's solution and heats it, but the colour remains blue. What does this indicate?
Medium
- AThe sample contains starch but no reducing sugar.
- BThe sample contains reducing sugar but no starch.
- CThe sample contains neither starch nor reducing sugar.
- DThe sample contains both starch and reducing sugar.
23.In the ethanol emulsion test for lipids, what is the positive result?
Easy
- AA blue-black colour
- BA brick-red precipitate
- CA cloudy white emulsion
- DA violet colour
24.Which row correctly matches the food test with its positive result?
Easy
- ABenedict's test: blue to violet
- BIodine test: orange-brown to blue-black
- CBiuret test: blue to brick red
- DEmulsion test: cloudy to clear
25.A student adds DCPIP to a sample of orange juice. The blue colour disappears. What does this indicate?
Easy
- AThe orange juice contains vitamin C
- BThe orange juice contains a reducing sugar
- CThe orange juice contains starch
- DThe orange juice contains protein
26.A food sample is tested with Biuret solution and turns violet. Which nutrient is present?
Easy
- AProtein
- BStarch
- CLipid
- DReducing sugar
27.A student tested a food sample and obtained the following results: iodine test – blue-black; Benedict's test (after heating) – brick-red; Biuret test – blue; emulsion test – cloudy white. Which nutrients are present?
Medium
- AStarch, reducing sugar, and lipid
- BStarch, protein, and lipid
- CReducing sugar, protein, and lipid
- DStarch, reducing sugar, and protein
28.A student performed the ethanol emulsion test on a sample of butter. After shaking with ethanol and adding cold water, a cloudy white emulsion formed. What does this result indicate?
Easy
- AButter contains lipids.
- BButter contains protein.
- CButter contains starch.
- DButter contains reducing sugar.
29.A sample of DNA has the base sequence A C G T on one strand. What is the sequence on the complementary strand?
Easy
- AT G C A
- BU G C A
- CA C G T
- DG C A T
30.Which of the following is the basic unit of a carbohydrate?
Easy
- AAmino acid
- BFatty acid
- CGlycerol
- DSimple sugar
31.All proteins are made from long chains of amino acids.
Easy
True or false?
32.Which food test uses ethanol and cold water to detect the presence of lipids?
Easy
- ABenedict's test
- BBiuret test
- CEmulsion test
- DIodine test
33.DNA is made up of nucleotides that contain a phosphate, a deoxyribose sugar, and a base.
Easy
True or false?
34.Which of these is a polysaccharide?
Easy
- AGlucose
- BMaltose
- CSucrose
- DGlycogen
35.What colour change indicates a positive result for the Benedict's test for reducing sugars?
Easy
- ABlue to violet
- BBlue to brick red
- COrange-brown to blue-black
- DBlue to colourless
36.Put the following in order of size from smallest to largest: amino acid, protein, gene, nucleus.
Medium
- amino acid
- protein
- gene
- nucleus
37.Match each food test to the correct positive result.
Medium
- Benedict's test for reducing sugars
- Iodine test for starch
- Biuret test for protein
- Ethanol emulsion test for lipids
- Blue to brick-red
- Orange-brown to blue-black
- Blue to violet/purple
- Cloudy white emulsion
38.Complete the sentence about DNA base pairing.
Easy
In DNA, adenine always pairs with ____, and cytosine always pairs with ____.
39.Name the two types of molecule that make up the 'backbone' of a DNA strand.
Easy
The backbone of a DNA strand is made of ____ and ____.
40.Describe how you would test a food sample for the presence of protein. Include the reagent used, the method, and the positive result.
Medium

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