University Biochemistry Module: Chemical Reactions in Living Systems

This report provides a comprehensive overview of biochemistry, focusing on the complex chemical reactions within living systems. It explores the structure and function of biomolecules, cellular metabolism, and product synthesis, highlighting the roles of enzymes, co-enzymes, and ATP. The report details key biochemical pathways like glycolysis, the TCA cycle, and the Krebs cycle, along with the structure and function of animal cells, including organelles such as the nucleus, ribosomes, mitochondria, and endoplasmic reticulum. It discusses DNA replication, cell division (mitosis and meiosis), and the genetic code, including the central dogma, transcription, translation, and the Human Genome Project. The report also touches upon genetics concepts such as dominant and recessive genes, sex-linked traits, and incomplete dominance. References to relevant research papers are included.

Running head: BIOCHEMISTRY LEARNING
Biochemistry Learning
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The following entails a brief discussion of the biochemistry module of learning.
Biochemistry deals with the complex chemical reactions that take place in the living systems,
focussing on the structure and function of the biomolecules. The cellular metabolism and
product synthesis are the components of biochemistry. Enzymes and co-enzymes play a
crucial role in biochemical reactions. ATP is the universal energy currency of the living cells
(Kee et al. 2013). Glycolysis, TCA cycle and Krebs cycle are examples of biochemical
pathways.
The animal cells comprise of the cytoplasm and nucleus with double membrane
bound organelles scattered throughout the cytoplasm. The cytoplasm is constituted by cytosol
or fluid part and cytoskeleton containing the micro tubular components involved in cell cycle.
Double membrane bound organelles are ribosomes (protein synthesis), mitochondria (site of
ATP synthesis), endoplasmic reticulum (RER containing ribosomes and SER involved in
lipid and glycogen synthesis), lysosomes, golgi apparatus (protein packaging). The nucleus,
consisting of nuclear membrane, nucleolus, nucleoplasm and nuclear envelope, is the primary
organelle containing the DNA in association with histones. Size of DNA molecule is 2M; it is
highly compressed to accommodate into the nucleus of a cell (20 μM).
During cell division, the DNA replicates to form a higher order structure called the
chromosomes, each consisting of two chromatids. Somatic chromosomes take part in mitosis;
sex chromosomes undergo meiosis. Chromosomes contain the hereditary gene sequences.
Specific locations of genes on a chromosome are termed as locus. Cell division or cell cycle
consists of interphase followed by mitosis. Interphase is divided into G1 phase (preparing the
cell to replicate), S phase (new DNA strand synthesis) and G2 phase (preparing the cell for
mitosis). Doubling of centrioles occurs in interphase. Identical daughter DNA strands are
synthesized in mitosis.

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Mitosis is divided into prophase, metaphase, anaphase and telophase. Prophase begins
by chromatin condensation and ends with disappearance of nuclear envelope. In metaphase
the chromosomes are aligned on the metaphasic plate and are ready for poleward movement.
Anaphase occurs through spindle fibre contraction; chromatid pairs from each chromosome
are pulled towards the opposite poles. The mitochondria provides the energy for spindle
contraction. The telophase is characterized by the cytoplasmic constriction followed by
splitting of the cell membrane. New nuclear membrane develops, spindle fibres disappear.
Two daughter cells are produced which are identical copies of their parental DNA. Meiosis is
the reductional cell division; mitosis is the equational cell division. Meiosis results into 4
haploid gametes whereas the number of gametes remain the same for mitotic division. Sex
chromosomes proceed through mitosis, then progresses through meiosis which results in
splitting of cells into 4 (Bertoli et al. 2013). The process of crossing over of genetic elements
occurs in meiosis; this results in variation among organisms. Chiasma is the point of crossing
over.
Genes are either dominant or recessive; dominant genes leads to the phenotypic
expression and masks the recessive expression. Albinism is a recessive disease involved in
faulty melanin synthesis. Sex-linked traits occur due to genes located on either X or Y
chromosomes (Ohno 2013). Haemophilia is an X-linked disorder; the faulty gene is located
on the X chromosome and thus affects only females. Incomplete dominance occurs when the
dominant genes do not complete mask the recessive gene expression; sickle cell anaemia is
an example. There are exceptions to dominance and recessivity. Some traits are controlled by
multiple genic interactions; the ABO blood group being an example. When more traits are
governed by multiple alleles, they are polygenic traits.
DNA and RNA are the principally abundant nucleic acids. The basic structural
components in nucleic acids are sugars (deoxyribose in DNA and ribose in RNA) and

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phosphates. The DNA strands are twisted in antiparallel fashion constituting the alpha helix;
the two strands being held together by weak hydrogen bonds. The component bases are
purines (adenine and guanine) and pyrimidines (thymine, cytosine, uracil) which undergo
complementary base pairing (Saenger 2013). DNA replication occurs by fork movement in
opposite direction through replication bubble formation. Semiconservative mode of
replication occurs which leads to two new daughter strands each with a copy of parental
strand. The leading strand synthesis occurs in 5’-3’ direction whereas the lagging strand
synthesis occurs in 3’-5’ direction through Okazaki fragment formation.
The central dogma constitutes the DNA transcribed to form mRNA which is
translated into proteins (O’Donnell, Langston and Stillman 2013). Transcription regulation
involves promoters and activators. Introns are spliced out and exons are joined in mature
mRNA. The genetic code consists of triplet codons. Amino acids are the building blocks of
proteins; proteins fold into 3D structure, characteristic of its function (Koonin 2015). The
Human Genome Project has sequenced all the DNA in human cell consisting of 3.2 billion
base pairs.

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References
Bertoli, C., Skotheim, J.M. and De Bruin, R.A., 2013. Control of cell cycle transcription
during G1 and S phases. Nature reviews Molecular cell biology, 14(8), p.518.
Kee, T.P., Bryant, D.E., Herschy, B., Marriott, K.E., Cosgrove, N.E., Pasek, M.A., Atlas,
Z.D. and Cousins, C.R., 2013. Phosphate activation via reduced oxidation state phosphorus
(P). Mild routes to condensed-P energy currency molecules. Life, 3(3), pp.386-402.
Koonin, E.V., 2015. Why the Central Dogma: on the nature of the great biological exclusion
principle. Biology direct, 10(1), p.52.
O’Donnell, M., Langston, L. and Stillman, B., 2013. Principles and concepts of DNA
replication in bacteria, archaea, and eukarya. Cold Spring Harbor perspectives in
biology, 5(7), p.a010108.
Ohno, S., 2013. Sex chromosomes and sex-linked genes (Vol. 1). Springer Science &
Business Media.
Saenger, W., 2013. Principles of nucleic acid structure. Springer Science & Business Media.