The document outlines the structure and function of DNA and RNA, emphasizing their roles in genetic information, protein synthesis, and gene expression. It details the processes of transcription and translation, including the roles of mRNA, tRNA, and rRNA in assembling proteins, as well as post-translational modifications and protein degradation. Additionally, it discusses protein secretion mechanisms and the significance of these processes in cellular function and health.

1. Genetic information and
Protein Synthesis:
Presented by : Dr Asiya Ramzan

2.  DNA AND RNA STRUCTURE
 GENE
 GENETIC CODE
 PROTEIN SYNTHESIS / GENE EXPRESSION
/REPLICATION AND EXPRESSION OF GENETIC
INFORMATION
 PROTEIN DEGRATION
 PROTEIN SECRETION
CONTENT

3.  INTRODUCTION
DNA, or deoxyribonucleic acid, is a molecule that
holds genetic information passed to an
organism’s offspring.
Genes are specific sections of DNA. DNA is
located in the cell nucleus (within chromosomes)
and also in the mitochondria. Nuclear DNA helps
form RNA, which guides protein synthesis, while
mitochondrial DNA is known as non-
chromosomal DNA
DEOXYRIBONUCLEIC ACID(DNA)

4. STRUCTURE OF DNA
DNA is structured as a double helix, which
resembles a twisted ladder. This structure
consists of two long chains (or strands) of
nucleotides that coil around each other.
 Each nucleotide in DNA is made up of:
 A phosphate group
 A sugar molecule (deoxyribose)
 A nitrogenous base: adenine (A), thymine (T),
cytosine (C), or guanine (G)

5.  The strands of DNA are arranged in such a way that both are
bound by specific pairs of bases.
 The adenine of one strand binds specifically with thymine of
opposite strand.
 Similarly, the cytosine of one strand binds with guanine of
the other strand
 This pairing is essential for DNA’s ability to replicate
accurately. DNA replication allows cells to pass genetic
information to their offspring,
 DNA forms the component of chromosomes, which carries
the hereditary information.
 The hereditary information that is encoded in DNA is called
genome.

7. INTRODUCTION
 Ribonucleic acid (RNA) is a nucleic acid that
contains a long chain of nucleotide units.
 It is similar to DNA but contains ribose instead
of deoxyribose.
 Various functions coded in the genes are
carried out in the cytoplasm of the cell by RNA.
RNA is formed from DNA
RIBONUCLEIC ACID (RNA)

8. STRUCTURE OF RNA
Each RNA molecule consists of a single strand of
polynucleotide unlike the double stranded DNA.
Each nucleotide in RNA is formed by:
1. Ribose – sugar.
2. Phosphate.
3. Nitrogenous Bases: RNA contains four nitrogenous
bases, which are:
Adenine (A)
Uracil (U) (replaces thymine found in DNA)
Cytosine (C)
Guanine (G)

9.  In RNA, adenine pairs with uracil (A-U), and
cytosine pairs with guanine (C-G). These base
pairs are formed through hydrogen bonding,
though RNA is typically single-stranded and can
fold back on itself to form various structures
that influence its function.

11. RNA is of three types.Each type of RNA plays a
specific role in protein synthesis
The three types of RNA are
1) MESSENGER RNA—THE CODONS
Messenger RNA carries the genetic code of the
amino acid sequence for synthesis of protein
from the DNA to the cytoplasm.
TYPES OF RNA

12.  Structure and Composition
mRNA molecules are long, single-stranded RNA
chains found in the cytoplasm, made up of hundreds
to thousands of unpaired RNA nucleotides. These
nucleotides form codons, which are three-nucleotide
sequences directly complementary to the DNA code.
 Codons and Amino Acids
Each codon in mRNA codes for a specific amino acid.
For example, codons CCG, UCU, and GAA correspond
to the amino acids proline, serine, and glutamic acid,
respectively

13.  Codons for Protein Synthesis
There are 20 amino acids, and most have multiple
codons. Additionally, specific codons signal the start
and stop of protein synthesis:
Total number of codon is 64
 Start Codon (CI): Signals the beginning of protein
synthesis.
1 Starting codon (AUG)
 Stop Codons (CT): Signals the end of protein
synthesis.
3 Stop codon (UAA), (UGA), (UAG)

14. 2) TRANSFER RNA—THE ANTICODONS
Role in Protein Synthesis
Transfer RNA (tRNA) plays a key role in protein
synthesis by transporting amino acids to the
growing protein chain. Each type of tRNA binds
specifically to one of the 20 amino acids, acting
as a carrier to deliver it to the ribosome during
protein formation.

15.  Structure and Function
tRNA is a small molecule with about 80 nucleotides. It
has a unique cloverleaf structure with a binding site
for an amino acid at one end. Each tRNA has an
anticodon, a sequence of three bases that pairs with a
specific codon on mRNA, ensuring the correct amino
acid is added to the protein sequence.
 Anticodon-Codon Interaction
The anticodon on tRNA binds to the complementary
codon on the mRNA strand. This interaction helps
arrange amino acids in the correct order, creating the
intended protein structure.

16. 3) Ribosomal RNA (rRNA)
 Role in Protein Synthesis
Ribosomal RNA (rRNA) makes up about 60% of the
ribosome, with the remaining 40% consisting of
around 75 proteins. The ribosome is the cell’s
protein-synthesis site, working together with
mRNA and tRNA.
 Function with Other RNA Types
tRNA brings amino acids to the ribosome.
mRNA provides the sequence instructions for the
amino acids.

17.  Ribosome as a Protein Factory
The ribosome acts like a manufacturing plant,
where proteins are assembled in the correct
order based on the mRNA instructions.

18.  INTRODUCTION
 Definition:
A portion of DNA carrying the code for
synthesizing a specific protein.
Acts like a book containing instructions for protein
synthesis.
 Protein Synthesis Role:
 Genes provide the instructions for assembling
proteins from amino acids in the ribosome
(outside the nucleus).
 There are 20 amino acids, each with a unique
codon.
Gene

19. STRUCTURE OF GENE
1) Promoter Region
 Location: Upstream of the coding region (at
the start of the gene).
 Function:
◦ Initiates transcription by providing a binding site for
RNA polymerase and transcription factors.
Key Features: TATA box (common sequence that aids
RNA polymerase binding

20. 2) Coding Region (Exons and Introns)
 Exons:
◦ Contain the actual coding sequences for proteins.
◦ Translated into amino acid sequences during protein
synthesis.
 Introns:
◦ Non-coding regions interspersed between exons.
◦ Spliced out during mRNA processing.
 Function: Provides the instructions for
synthesizing functional proteins or RNA
molecules.

21. 3)Terminator Region
 Location: Downstream of the coding region (at
the end of the gene).
 Function:
◦ Signals the termination of transcription.
◦ Causes RNA polymerase to detach from the DNA
template

23.  What is the Genetic Code?
 Definition: The genetic code is a sequence of
nucleotide triplets in DNA and RNA that
specifies the amino acid sequence in proteins.
 Function: Enables cells to translate genetic
information into functional proteins.
 The set of rules by which DNA and RNA
sequences are translated into proteins.
Genetic Code

24.  Gene expression is the process by which the
information (code word) encoded in the gene is
converted into functional gene product or
document of instruction (RNA) that is used for
protein synthesis.
 Gene expression involves two steps:
1. Transcription.
2) Translation
GENE EXPRESSION

25.  The transcription process in cells is a multi-step
mechanism where DNA is used as a template to
synthesize RNA.
1) Initiation
 Promoter Recognition: Transcription begins
when the enzyme RNA polymerase binds to a
specific DNA sequence known as the promoter,
located just before (upstream of) the gene to be
transcribed.
 RNA Polymerase Attachment: The RNA
polymerase recognizes and attaches to the
promoter region. This step ensures that
transcription begins at the correct location on the
DNA.
1)Transcription.

27. 2) DNA Unwinding
 Helix Unwinding: After attaching to the
promoter, RNA polymerase unwinds a small
section of the DNA double helix (about two
turns), breaking the hydrogen bonds between
the DNA strands.
 Strand Separation: This creates a transcription
bubble, exposing the DNA template strand,
which will be used to build the complementary
RNA strand.

28. 3) Elongation
 Template Strand Selection: RNA polymerase moves
along the DNA, using the exposed template strand to
assemble a complementary RNA sequence.
 RNA Nucleotide Pairing:
◦ RNA nucleotides in the cell nucleus align with their
complementary DNA bases on the template strand.
◦ For example:
 DNA Adenine (A) pairs with RNA Uracil (U)
 DNA Thymine (T) pairs with RNA Adenine (A)
 DNA Cytosine (C) pairs with RNA Guanine (G)
 DNA Guanine (G) pairs with RNA Cytosine (C)

29.  Energy Release and Covalent Bond Formation:
RNA polymerase cleaves two phosphates from
each incoming RNA nucleotide, releasing energy.
 This energy is used to form a covalent bond
between the ribose sugar of one nucleotide and
the phosphate of the next, extending the RNA
chain.
 Movement Along DNA: RNA polymerase
continues to move along the DNA strand,
repeating this process to elongate the RNA
molecule.

31. 4) Termination
 Chain-Terminating Sequence: When RNA
polymerase reaches a DNA sequence called the
terminator, the transcription process stops.
 Release of RNA Strand: The RNA polymerase
detaches from the DNA, and the newly
synthesized RNA strand is released. This RNA
may now undergo further processing.

32. RNA Processing (in Eukaryotes
 Pre-mRNA Modifications: In eukaryotic cells, the initial
RNA strand produced is called pre-mRNA. It undergoes
several modifications to become mature mRNA:5'
Capping: A modified guanine nucleotide cap is added to
the 5' end of the RNA for stability and to aid ribosome
binding during translation.
 Polyadenylation: A tail of adenine nucleotides (poly-A tail)
is added to the 3' end, providing further stability.
 Splicing: Non-coding regions (introns) are removed, and
coding regions (exons) are joined together by small nuclear
RNAs (snRNAs) in a complex called the spliceosome.

33.  Export to Cytoplasm: The mature mRNA,
containing only exons, exits the nucleus and
enters the cytoplasm to participate in protein
synthesis

35.  The translation process in cells is the mechanism by which
the genetic code in messenger RNA (mRNA) is used to
synthesize a protein.
1) Initiation
 mRNA Binding to Ribosome: The mRNA, which has been
transcribed from DNA, exits the nucleus and binds to a
ribosome in the cytoplasm. The ribosome reads the mRNA
code to assemble the protein.
 Start Codon Identification: The ribosome identifies the
start codon (AUG) on the mRNA, which signals the
beginning of the protein. This codon codes for the amino
acid methionine, which will be the first amino acid in the
protein chain.
2) Translation

36.  tRNA Binding: A transfer RNA (tRNA) molecule
with an anticodon complementary to the start
codon (UAC for AUG) binds to the mRNA. This
tRNA carries methionine, the first amino acid in
the sequence.

38. 2) Elongation
 Reading of Codons: After the start codon, the
ribosome continues to read the mRNA in
groups of three nucleotides called codons. Each
codon corresponds to a specific amino acid

39. tRNA Matching and Amino Acid Addition:
 For each mRNA codon, a corresponding tRNA
molecule with a complementary anticodon binds
to the ribosome.
 Each tRNA carries a specific amino acid that
corresponds to its anticodon.
Peptide Bond Formation:The ribosome catalyzes
the formation of a peptide bond between the
amino acid of the new tRNA and the growing
protein chain.
 The ribosome moves along the mRNA, releasing
the empty tRNA and positioning the next tRNA
with the appropriate amino acid.
 This process continues, elongating the protein
chain one amino acid at a time.

42. 3) Translocation
 Ribosome Movement: The ribosome moves
along the mRNA strand one codon at a time,
positioning each new codon in the ribosome’s
active site to ensure that the correct tRNA
binds.
 Polypeptide Chain Growth: With each step,
the polypeptide chain grows as amino acids are
added in the sequence specified by the mRNA
codons.

44. 4) Termination
 Stop Codon Recognition: When the ribosome reaches
a stop codon (UAA, UAG, or UGA) on the mRNA,
translation is halted because no tRNA corresponds to
these stop codons.
 Release of Polypeptide Chain: A protein called release
factor binds to the ribosome, prompting it to release
the completed polypeptide (protein) chain from the
tRNA.
 Ribosome Disassembly: The ribosome detaches from
the mRNA, and its subunits dissociate, ready to be
used again for another round of translation.

47. Folding and Processing: After release, the
polypeptide chain may need to fold into its
functional three-dimensional structure, often
with the help of proteins called chaperones
Chemical Modifications: The protein may
undergo additional modifications called post
translational modification.
Definition (PTM)
PTMs are chemical changes to a protein after it
has been synthesized (translated) in the cell.
Post Translational Modification

48. Types
1. Phosphorylation
2. Glycosylation
3. Acetylation
4. Ubiquitination
5. Methylation
6. Lipidation

50. 1) Phosphorylation
Definition:
Addition of a phosphate group, usually to serine,
threonine, or tyrosine residues.
Enzymes Involved: Kinases and phosphatases.
Function:
Regulates enzyme activity Key role in cell
signaling and metabolic pathways

51. 2) Glycosylation
 Definition: Addition of carbohydrate groups to
proteins.
Types:
N-linked glycosylation
O-linked glycosylation
Function:
 Important for cell recognition, immune
response, and protein stability.

52. 3) Acetylation
Definition: Addition of an acetyl group, often to
lysine residues.
Key Enzymes: Histone acetyltransferases (HATs)
and histone deacetylases (HDACs).
Function:
 Regulates gene expression (e.g., histone
modification)Impacts protein stability and
interactions.

53. Physiological Importance of PTMs
 Role in Cell Signaling: Modifies activity of
signaling proteins.
 Regulation of Gene Expression: Histone
modification by acetylation and methylation.
 Protein Quality Control: Ubiquitination marks
damaged proteins for degradation.

54.  Clinical Relevance Disease Links:
Abnormal phosphorylation in cancer and
diabetes
Defective ubiquitination in neurodegenerative
diseases

55.  What is Protein Degradation?
A biological process where cells break down
proteins into amino acids.
Essential for regulating protein levels, removing
damaged proteins, and recycling amino acids.
Importance of Protein Degradation
Maintains protein balance (proteostasis) in cells.
Eliminates damaged or misfolded proteins.
Regulates various cellular processes (e.g., cell
cycle, immune response).
Protein Degradation

56. Two Main Protein Degradation Pathways
1) Ubiquitin-Proteasome System (UPS)
Process:
Ubiquitination - Proteins tagged with ubiquitin.
Recognized by the proteasome. Proteasome
degrades protein, releasing peptides and amino
acids.
Importance: Degrades short-lived and
misfolded proteins

57. 2) Autophagy-Lysosome Pathway
Autophagy involves the engulfment of cellular
components in vesicles.
Lysosomes degrade the contents.
Role: Removes damaged organelles and proteins
Types of Autophagy:
1)Macro autophagy (most common)
2)Micro autophagy
3) Chaperone-mediated autophagy

58. Process:
• Cellular components are enclosed in
autophagosomes.
• Autophagosomes fuse with lysosomes.
• Lysosomal enzymes degrade components

59.  Significance in Health and Disease
Normal Conditions: Maintains cell health,
nutrient recycling
Diseases Dysfunction can lead to:
1)Cancer (unregulated protein degradation).
2) Neurodegenerative disorders (accumulation of
misfolded proteins).
3)Muscle wasting, autoimmune diseases.

60.  What is Protein Secretion?
 Definition: The process by which cells release
proteins to the extracellular environment.
 Importance:
◦ Hormone release (e.g., insulin).
◦ Enzyme secretion (e.g., digestive enzymes).
◦ Immune responses (e.g., antibodies)
Protein Secretion

61.  Key Components Involved
 Ribosomes: Synthesize proteins.
 Rough Endoplasmic Reticulum (RER): Protein
folding and initial modification.
 Golgi Apparatus: Final processing and sorting.
 Secretory Vesicles: Transport proteins to the
cell membrane.
 Plasma Membrane: Facilitates protein release
via exocytosis

62. Steps in Protein Secretion
 Protein Synthesis:
◦ Translation of mRNA occurs in ribosomes on the RER.
 Folding and Modification in ER:
◦ Proteins are folded into their functional shapes and undergo
glycosylation.
 Transport to Golgi:
◦ Vesicles carry proteins from the ER to the Golgi apparatus.
 Processing in Golgi Apparatus:
◦ Proteins are further modified (e.g., phosphorylation,
glycosylation).
 Packaging into Vesicles:
◦ Golgi sorts proteins into vesicles for specific destinations.
 Exocytosis:
◦ Vesicles fuse with the plasma membrane to release proteins
outside the cell.

63.  Types of Secretion
 Constitutive Secretion:
◦ Continuous process.
◦ Example: Secretion of extracellular matrix proteins.
 Regulated Secretion:
◦ Requires a specific stimulus (e.g., hormone or
neurotransmitter).
◦ Example: Insulin secretion in response to glucose

64.  Regulation of Protein Secretion
Signals for Secretion:
◦ Hormonal signals (e.g., insulin secretion via glucose).
◦ Neural signals (e.g., neurotransmitter release).

65.  "Guyton and Hall Textbook of Medical
Physiology"
 "Ganong's Review of Medical Physiology.“
 K Sembulingam, prema Sembulingam
Essential of Medical
 “Human physiology “Stuart Ira Fox Pierce
College
REFERENCE