How many different amino acids are commonly found in the proteins of living organisms, and what distinguishes them?

There are twenty, and they differ only in their R groups.

Why does the R group of an amino acid matter so much to the protein it is part of?

The R groups may be charged, polar, non-polar or able to form disulfide bridges, and the interactions between them determine how the polypeptide folds and therefore the shape and function of the finished protein.

How is a peptide bond formed?

The carboxyl group of one amino acid reacts with the amino group of the next in a condensation reaction, releasing a molecule of water and leaving a −CO−NH− link between them.

How many water molecules are released when a polypeptide of 100 amino acids is assembled?

Ninety-nine, because there is one peptide bond, and therefore one condensation reaction, between each adjacent pair.

Why is paper chromatography able to separate a mixture of amino acids?

Each amino acid has a different solubility in the mobile solvent and a different attraction to the water held in the stationary paper, so each travels a different distance as the solvent moves up the paper.

OCR A-Level Biology B H422

The Developing Cell: Cell Division and Cell Differentiation

Topic overview The cell cycle and mitosis Apoptosis in growth and repair Stem cells and cell differentiation

The Developing Individual: Meiosis, Growth and Development

Topic overview Meiosis, haploid gametes and genetic variation The stages of meiosis Antenatal care and diet in pregnancy Alcohol, smoking and monitoring fetal growth Prenatal screening and karyotypes

The Development of Species: Evolution and Classification

Topic overview Classification and the species concept Evidence for classification and DNA barcoding Phylogenetic trees, hominids and the evolution of language Human adaptations, natural selection and evolution Plant adaptations and how they are investigated Measuring biodiversity and genetic diversity

Cells and Microscopy

Topic overview Microscopy and the cell theory Blood smears, staining and microscope drawings Blood cells and their structure Magnification and measuring cells Haemocytometer cell counts and dilutions Flow cytometry in blood analysis Ultrastructure of the animal cell Plant and prokaryotic cells Membrane lipids and the fluid mosaic model Movement of molecules across membranes The roles of membranes and the secretion of proteins

Water and Its Importance in Plants and Animals

Topic overview The properties of water Water as a transport medium and the composition of body fluids Detecting and measuring sugars and proteins Monomers, polymers and the carbohydrates Osmosis and water potential

Proteins and Enzymes

Topic overview Amino acids, peptide bonds and chromatography Globular protein structure: enzymes and haemoglobin Enzyme action and the rate of reaction Blood clotting and first aid Enzymes and inhibitors in medicine Blood donation and stored blood products

Nucleic Acids

Topic overview Nucleotides, ADP and ATP The structure of DNA and its extraction DNA replication and the genetic code RNA, transcription and translation

Patterns of Inheritance

Topic overview Monogenic inheritance and genetic terminology Gene mutations and inherited disease Codominance, multiple alleles and linkage Model organisms, dihybrid crosses and the chi-squared test Chromosome mutations and genetic counselling

Population Genetics and Epigenetics

Topic overview Natural selection, sickle cell and malaria The Hardy-Weinberg principle Genetic drift, the founder effect and speciation Epigenetics and gene expression

Gene Technologies

Topic overview Post-Transcriptional Editing of mRNA Genetic modification of bacteria and insulin production The polymerase chain reaction and gel electrophoresis Haplotypes, SNPs, VNTRs and genetic engineering in eukaryotes Gene therapy and RNA interference

The Principles and Importance of Homeostasis

Topic overview Homeostatic principles, normal ranges and feedback The nervous and hormonal control of heart rate The control of body temperature and the role of thyroxine Measuring core body temperature, hypothermia and hyperthermia

The Hormonal Control of Blood Glucose and the Management of Diabetes

Topic overview The pancreas as an endocrine gland The regulation of blood glucose by negative feedback Types of diabetes and diagnostic testing Treating and managing diabetes

Kidney Functions and Malfunctions

Topic overview Excretion and the gross structure of the kidney The nephron: ultrafiltration and selective reabsorption Investigating the composition of urine, plasma and filtrate Osmoregulation and the action of ADH The kidney as an endocrine gland and kidney failure Dialysis, transplantation and the future of transplant surgery

The Cellular Basis of Cancer and Treatment

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Respiratory Diseases and Treatment

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Cellular Respiration

Topic overview Glycolysis and the link reaction The Krebs cycle Oxidative phosphorylation and anaerobic respiration Respiratory substrates and respiratory quotients Measuring the rate of respiration

Metabolism and Exercise

Topic overview The consequences of exercise on the body Aerobic fitness and VO₂ max Training, F.I.T.T. factors and investigating fitness Enhancing athletic performance Haemoglobin and the transport of oxygen Oxygen dissociation curves of different respiratory pigments Oxygen deficit and oxygen debt The structure of skeletal muscle The sliding filament theory of muscle contraction

Pathogenic Microorganisms

Topic overview How pathogens cause communicable disease Tuberculosis HIV, AIDS and the structure of the virus Identifying bacteria: Gram staining and culture Epidemiology: incidence, prevalence and mortality Notifiable diseases and the control of HIV and TB

The Immune System

Topic overview Primary defences and non-specific responses B and T lymphocytes and the specific response Antibodies and testing for TB and HIV Types of immunity and allergy

Controlling Communicable Diseases

Topic overview Vaccination and vaccination programmes Problems and ethics of vaccine development and use Antibiotics and antibiotic resistance Investigating antibiotics, disinfectants and hygiene

Photosynthesis, Food Production and Management of the Environment

Topic overview Chloroplast ultrastructure and photosynthetic pigments The light-dependent stage of photosynthesis The Calvin cycle Investigating the factors affecting photosynthesis The Hill reaction and DCPIP Using TP and GP to build carbohydrates, lipids and amino acids The compensation point and crop production Microorganisms, the nitrogen cycle and biosensors Biomass transfer and efficiency in food production Ruminants in the human food chain Farms as ecosystems and the conflict with conservation Deflected succession and measuring biodiversity

The Impact of Population Increase

Topic overview Birth rate, death rate and demographic change Human impact on ecosystems and biodiversity The importance and measurement of species biodiversity Global food security and sustainable food production

Planning and Implementing Practical Work

Topic overview Designing an investigation and controlling variables Choosing apparatus and judging whether a method will work Implementing: apparatus, units and recording results

Analysing and Evaluating Practical Results

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Practical Skills, Apparatus and Techniques

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Fertility and Assisted Reproduction

Topic overview The urinogenital systems and gonad histology Gametogenesis and the structure of the gametes Hormonal control of gametogenesis and the menstrual cycle Fertilisation and pregnancy testing The causes and issues of infertility Assisted reproduction techniques

The Effects of Ageing on the Reproductive System

Topic overview Ageing and the female reproductive system Managing the menopause Ageing and the male urinogenital system

Plant Reproduction

Topic overview The control of flowering Adaptations of flowers for pollination Fertilisation, seed formation and germination Cereals as staple foods

The Nervous System and the Identification and Consequences of Damage

Topic overview Organisation of the nervous system and nervous tissue The structure and function of the human brain The structure of motor, sensory and relay neurones Resting potential and the action potential Synapses and the integration of responses Reflexes, reaction times and their investigation Brain scans and the consequences of nervous system damage Drugs, brain function and dependency

Monitoring Visual Function

Topic overview The structure of the eye The retina and its role as a transducer Assessing visual function by routine eye tests

The Effect of Ageing on the Nervous System

Topic overview Alzheimer's disease: symptoms and causes The effects of ageing on the senses and memory Investigating ageing, reaction times and memory

The Heart and Monitoring Heart Function

Topic overview The need for a mass transport system Structure and dissection of the mammalian heart The cardiac cycle Initiation and coordination of the heartbeat Heart rate, pulse rate and cardiac output Electrocardiograms and emergency cardiac treatment

Transport Systems in Mammals

Topic overview The closed double circulatory system Blood vessels and their microscopic structure Tissue fluid and capillary exchange Measuring and interpreting blood pressure

Gas Exchange in Mammals and Plants

Topic overview Tissues of the mammalian gas exchange system Gas exchange in the alveoli Pulmonary ventilation and lung volumes Expired air resuscitation Gas exchange and stomata in terrestrial plants

Transport Systems in Plants

Topic overview The need for transport systems in plants Vascular tissue in roots, stems and leaves Water uptake and movement through the plant Transpiration and Its Measurement Translocation in the Phloem

Proteins and Enzymes

Amino acids, peptide bonds and chromatography

3 things to know
Components 01, 02 and 03

Overview

Recall questions on the structure of amino acids and their R groups, peptide bond formation, running a paper chromatogram of amino acids, developing it with ninhydrin safely, calculating and using Rf values, and two-way chromatography.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Key term

Describe how a chromatogram of an amino acid mixture is prepared and run.

Key term

Why is the origin line of an amino acid chromatogram drawn in pencil rather than ink?

Key term

What is the general structure of an amino acid?

Questions from this subtopic

Each one with the model answer underneath.

1
What is the general structure of an amino acid?
Model answer
A central carbon atom is bonded to an amino group −NH₂, a carboxyl group −COOH, a hydrogen atom and a variable side chain known as the R group.
2
How many different amino acids are commonly found in the proteins of living organisms, and what distinguishes them?
Model answer
There are twenty, and they differ only in their R groups.
3
Why does the R group of an amino acid matter so much to the protein it is part of?
Model answer
The R groups may be charged, polar, non-polar or able to form disulfide bridges, and the interactions between them determine how the polypeptide folds and therefore the shape and function of the finished protein.
4
How is a peptide bond formed?
Model answer
The carboxyl group of one amino acid reacts with the amino group of the next in a condensation reaction, releasing a molecule of water and leaving a −CO−NH− link between them.
5
How many water molecules are released when a polypeptide of 100 amino acids is assembled?
Model answer
Ninety-nine, because there is one peptide bond, and therefore one condensation reaction, between each adjacent pair.
6
Why is paper chromatography able to separate a mixture of amino acids?
Model answer
Each amino acid has a different solubility in the mobile solvent and a different attraction to the water held in the stationary paper, so each travels a different distance as the solvent moves up the paper.

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The Developing Cell: Cell Division and Cell Differentiation

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The Development of Species: Evolution and Classification

Cells and Microscopy

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