Welcome to Stepping Up to Chemistry - the place to go for all students who want to brush up on their academic skills before starting university; covering everything from mathematics to note-taking in lectures.

The site has been specially designed by Chemistry students at York, sharing with you tips and advice based on what current students found most difficult when beginning the course.

To make the transition into University teaching that bit easier we have collected this guidance into five sections listed below, with additional practice problems for each section to help you test your understanding.

 

 

 

 

 

 

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We thank our undergraduate chemists who helped develop this project, in particular, Katie Lee for instigating the project, Elizabeth Wilcock for expanding the material and for work on the web (part-funded by the Careers Service) and more recently, Paige Boxhall and Jon Perrett for updating the site as part of their departmental summer vacation bursary.

It is also noted that our Year 1 recommended textbook, Chemistry3, has an online resource centre, including over 90 Chemistry videos, that you may find useful. 

The University launched a range of massive open online courses (MOOCs) in January 2017. Our Chemistry MOOC, ‘Exploring Everyday Chemistry offers a short, interactive, higher education experience and the chance to be part of a global learning community.

Register your interest

https://www.youtube.com/watch?v=ZDsJ8yrPEk4

Biological Molecules: Building blocks of life.

In your first year at University you will develop your understanding of the chemistry behind the important biological molecules vital for life on Earth. This section of the site will cover the key information required to understand the differences between biological molecules as well as their role in the survival of living cells. You will cover:

  • Lipids which include organic-soluble waxes, oils, fats and steroids.
  • Carbohydrates which are poly-hydroxycarbonyl compounds that exist as monomers, dimers or polymers.
  • Proteins which are natural polyamides produced from the condensation of amino acids.
  • DNA and RNA, these are natural polymers made up of sugars, heterocyclic nitrogen bases and phosphate groups. 

Lipids

Lipids

• Contain elements carbon, oxygen and hydrogen.

They are known as ‘fats’. Lipids can be used as an energy store. These 'fats' are formed from triglycerides, which are made from 3 fatty acids and a glycerol and these are connected by ester bonds

Ester Bonds: An ester bond is the bond between an alcohol group (-OH) and a carboxylic acid group (-COOH), formed by the elimination of a molecule of water (H2O).

Triglycaride, the R groups are fatty acid hydrocarbon chains.

 

Lipids can be saturated (contains only single bond between carbons in the hydrocarbon chain) or unsaturated (contains at least one double bond between carbons in the hydrocarbon chain).

Phospholipids replace a fatty acid group with a phosphate group. These are used to form the phospholipid bilayer in cell membranes. This bilayer has a hydrophobic centre, from the hydrocarbon fatty acid tails, and a hydrophilic surface, from the polar phosphate group. Thismakes the cell selective as polar molecules will need a intermembrane protein in order to enter the cell as they cannot pass through the hydrophobic environment.

Author accreditation: CNX OpenStax [CC BY 4.0 (https://creativecommons.org/licenses/by/4.0)]

 

P‌hospholipid with phosphate group replacing one of the fatty acids in a triglyceride. 

Carbohydrates

Carbohydrates

• Contain elements carbon, oxygen and hydrogen.

Monosaccharides

These are single unit sugars e.g. glucose, galactose and fructose

One way to classify monosaccharides is to use functional groups present in the molecule. A monosaccharide with a ketone group is called a ketose (fructose) and a monosaccharide with an aldehyde group is called an aldose (glucose).
 
 
 
Glucose exists in the form of two cyclic stereoisomers known as anomers, α-glucose and β-glucose, where configuration differs at the anomeric carbon (carbon 1). 
 
 
These sugars show mutarotation as the α and β anomeric forms interconvert. Mutarotation is a change in the specific rotation of a chiral compound at a given wavelength.
 

Disaccharides

These are two monosaccharides connected by a glyosidic bond.

For example; maltose (2x glucose), lactose (glucose and galactose), sucrose (glucose and fructose).

L‌actose shown above. 

Polysaccharides

These are long chains of monosaccharides connected by glycosidic bonds.

Some examples of polysaccharides:

Cellulose is a polysaccharide formed from β-glucose (image 2). Every other one flipped by 180° to give straight chains connected by H bonds. This results in a strong rigid structure and cellulose is used to form plant cell walls.

Dash lines represent H bonds between parallel chains. 

Starch is a polysaccharide formed from α- glucose. This gives two structures amylose (straight) and amylopectin (branched). Amylose can be folded into a helix to be stored efficiently as starch, which is used as a plant source of energy.

Glycogen is formed from amylose. The straight chains are easily broken down making it a energy source for animals.

Proteins

 

Proteins

Sub-Units

  • Made of amino acid sub-units, connected by peptide bonds.

An alpha amino acid contains an amino group and a carboxylic acid group, separated by one carbon, called the α-carbon. 

Amino acids can form zwitterions when a hydrogen is transferred from the acidic -COOH group to the basic -NH2. A zwitterion is a compound with no overall electrical charge but contains separate positively and negatively charged parts.

The simplest is glycine with H as the R group, next is alanine where R is CH3. There are 64 amino acids in total.

All amino acids, except Glycine, are chiral because they contain at least one chiral centre. A chiral molecule has a pair of non-superimposable mirror images. These isomers are referred to as R and S. All amino acids in proteins are S.

Structures

Joining two amino acids makes a dipeptide and linking many amino acids gives a polypeptide chain, the primary structure of a protein.

 

 

They then form an α -helix or β pleated sheet as their secondary structure. These are held together by hydrogen bonds between C=O and H-N groups on neighbouring amino acids. The exact pattern on these bonds determines whether an α -helix or β pleated sheet is formed. 

Author accreditation: OpenStax College [CC BY 3.0 (https://creativecommons.org/licenses/by/3.0)]

Additional bonds, such as disulphide bridges, ionic and hydrogen bonds, form between different amino acids R groups to give the final 3D structure of the protein known as the tertiary structure

Proteins have various functions including:

  • catalytic (enzymes)
  • structural (collagen)
  • messengers (hormones)
  • transport (intermembrane proteins)

DNA & RNA

DNA 

  • Deoxyribonucleic acid 

Made up of nucleotides forming polynucleotides with a sugar phosphate backbone and hydrogen bonds between nucleic acids.

 

Nucleotides consist of a nitrogenous base, sugar and phosphate. Nucelosides, however, do not include the phosphate, only the base and sugar.

The pentose sugar in DNA is deoxyribose.

Adenine (A) and thymine (T) have 2 hydrogen bonds between them but cytosine (C) and guanine (G) have 3 hydrogen bonds between them.

DNA is double stranded and undergoes semi conservative replication. This is replication in which the two original strands of the molecule separate, and each strand acts as a template for the synthesis of a new, complementary strand. Each new DNA molecule consists of one old strand and one new strand.

It stores genetic information needed to make proteins in the form of chromosomes (wound up DNA).

 RNA

  • Ribonucleic acid 

RNA is only a single strand of nucleotides, where the pentose sugar in the nucleotide is ribose

The nitrogenous bases can include adenine (A), cytosine (C), guanine (G) & uracil (U) (instead of thymine)

MRNA is used as a messenger between DNA and ribosomes (used in protein synthesis) in translation. Whereas tRNA is used as a carrier of amino acids in transcription