Unit 1a Biological Molecules Recall Questions answers

What elements are common to all the molecules of life?

C, O, H

What are the four main groups of carbon-based molecules common to all life forms?

Carbohydrates, Lipids, Proteins, Nucleic Acids

Which molecule forms part of the plasma membrane?

Phospholipids

Which two biological molecules are the main respiratory substrates?

Lipids and Carbohydrates

What is a polymer?

A series of repeating units (monomers) joined together

Which reaction breaks down polymers?

Hydrolysis

What type of chemical bond is formed between monomers?

Covalent bond

Why is it known as a condensation reaction?

A molecule of water is produced/released

What type of polymer is made from monosaccharides and what bond joins them together?

A polysaccharide – glycosidic bonds

What type of polymer is made from nucleotides and what bond joins them together?

A polynucleotide – phosphodiester bonds

What is a disaccharide? What type of bond is involved?

Two monosaccharides joined together by a glycosidic bond

What disaccharide is made by joining glucose and glucose?

Maltose

What are the two monosaccharides that join up to make sucrose?

Fructose and glucose

What disaccharide is made by joining glucose and galactose?

Lactose

What are the 3 types of polysaccharides that α-glucose can form?

Amylose, Amylopectin, Glycogen

What type of reaction breaks polysaccharides apart?

Hydrolysis

Describe the structure of glycogen.

Polymer of alpha glucose - highly branched

State the two structures that make up starch.

Amylose + Amylopectin

Describe the structure and properties of starch.

A mixture of two polysaccharides of alpha glucose.

Amylose is a long branched chain of glucose.

The angles of the glycosidic bonds give it a coiled structure which makes it compact so good for storage.

Amylopectin is a long branched chain of a glucose, its side branches allow enzymes to get at the glycosidic bonds easily so glucose can be released quickly.

It is insoluble in water.

What’s the differences and similarities between starch and glycogen?

Glycogen is always branched, starch isn't. Starch found in plants, glycogen in animals. Both are energy stores, both made of alpha glucose.

How are the monosaccharides in cellulose arranged?

Alternative β-glucose molecules are turned upside down.

Why are different enzymes needed to digest starch and cellulose?

different shape molecule requires a different enzyme as they have different active site shapes. cellulose is made of B glucose and starch of a glucose. 1,6 glycosidic bonds are only in starch. starch is made of amylose and amylopectin, cellulose is linear and starch is branched

Based on the arrangement of cellulose molecules, explain why cell walls provide strength and support to plant cells.

Cellulose molecules form hydrogen bonds to create microfibrils, making the fibers tough and flexible.

1,6 glycosidic bonds are found on __.

Amylopectin / Glycogen

β-glucose can only be found in __.

Cellulose

Describe the structure of amylopectin, including the bonds involved and the shape.

Amylopectin is a long branched chain of a glucose. its side branches,1,4 and 1,6 glycosidic bonds, branched

State 4 roles of lipids.

Source of energy, waterproofing, insulation, protection.

What does a triglyceride consist of? Which type of bonds hold it together?

Glycerol and 3 fatty acids - ester bonds.

How is a phospholipid different to a triglyceride? And how are they similar?

Only 2 fatty acids (Triglyceride has three). Phosphate head (triglyceride has no phosphate). Both have fatty acids.

How many water molecule(s) is/are needed when breaking down a triglyceride?

3

What does a triglyceride consist of? Which type of bonds hold it together?

Glycerol and 3 fatty acids - ester bonds.

Describe how phospholipids can form a bilayer arrangement.

- Hydrophilic heads point outwards
- Hydrophobic tails point inwards (shielded from aqueous environment)

Describe the test for a reducing sugar and state the positive result.

Add Benedict's reagent, heat; positive result = changes from blue to brick red.

What can be done if the test for a reducing sugar produces a negative result but sugars should be present?

Take another sample, add HCl, heat in water bath , neutralize with NaOH, then add Benedict’s and boil.

Why is the benedicts test known as a semi-quantitative test?

Because it tells you how much sugar there is, but not exactly how much (i.e. it's not quantitative)

How can we use a colorimeter to do a quantitative Benedict's test?

- Colorimeter measure the absorbance or transmission of light by a coloured solution - More concentrated solution à more light absorbed / less light transmitted - Compare to data table (known concentrations vs. abs/trans value)

Describe the test (and result) for proteins.

If the blue solution turns purple, it's a positive result.

Describe the steps in identifying lipids and state the positive result.

Mix sample with ethanol, then with water and shake ; a white emulsion layer indicates lipid presence.