The inherited DNA of an organism contains specific traits that dictate the synthesis of proteins through the RNA molecules involved in protein synthesis. In other words, proteins are the link between genotype and phenotype. Gene expression is the process by which DNA directs the synthesis of proteins (or, in some cases, just RNAs). The expression of genes that code for proteins includes two stages: transcription and translation. In this slide, we are going to take a look into the processes of replication and transcription.
DNA ارثی یک ارگانیسم حاوی صفات خاصی است که سنتز پروتئین‌ها را از طریق مولکول‌های RNA درگیر در سنتز پروتئین دیکته می‌کند. به عبارت دیگر، پروتئین‌ها رابط بین ژنوتیپ و فنوتیپ هستند. بیان ژن فرآیندی است که در آن DNA سنتز پروتئین‌ها (یا در برخی موارد فقط RNA ها( را هدایت می‌کند. بیان ژن‌هایی که برای پروتئین‌ها کد می‌کنند شامل دو مرحله است: رونویسی و ترجمه. در این اسلاید قصد داریم نگاهی به فرآیندهای همانندسازی و رونویسی بیاندازیم.
1. From DNA to Protein
(Replication and Transcription)
UNIVERSITY OF TEHRAN
Ahmad V.Kashani, PhD
2. Outlines
• DNA structure
• DNA Replication
• Replication models
• Origin of replication
• Replication components
• Leading Strand
• Lagging Strand
• DNA repair and proofreading
• Transcription
• Bacteria vs. Eukarya
• The Genetic Code
12. DNA Replication –
Leading Strand
• Based on conservative model of
replication, two forms of newly
synthesized strands are made
during replication process:
• Leading strand
• Lagging strand
17. DNA Repair & Proofreading
• The damaged DNA is cut by a DNA-cutting
enzyme called nuclease.
• The repairing enzymes are:
• DNA polymerase
• DNA ligase
• Example: DNA repair in skin cells to
correct genetic damages caused by the
ultraviolet ray of sunlight.
18. Replicating DNA ends
• Eukaryotes have repetitive, noncoding sequences
called telomeres at the ends of their DNA called
telomeres.
• Telomeres do not contain genes; instead, the DNA
typically consists of multiple repetitions of one
short nucleotide sequence.
• In each human telomere, for example, the six-
nucleotide sequence TTAGGG is repeated between
100 and 1,000 times.
22. The Genetic Code
• The triple code is the genetic
instructions for a polypeptide chain
are written in the DNA as a series of
non-overlapping, three-nucleotide
words.
• The template strand provides the
pattern, or template, for the sequence
of nucleotides in an RNA transcript.
• The non-template DNA strand is often
called the coding strand.
23. The Genetic Code
• The three nucleotide bases of an
mRNA codon are read in the 5’ to 3’
direction along the mRNA.
• The codon AUG not only stands for
the amino acid methionine (Met, or
M) but also functions as a “start”
signal for ribosomes to begin
translating the mRNA at that point
• The codons UAA, UAG, and UGA out
of the 64 codons function as “stop”
signals, marking where ribosomes end
translation.
26. Transcription stages in Eukarya –
Elongation & Termination
• Termination
• In eukaryotes, RNA polymerase II transcribes
a sequence on the DNA called the
polyadenylation signal sequence, which
specifies a polyadenylation signal (AAUAAA)
in the pre-mRNA.
• Then, at a point about 10–35 nucleotides
downstream from the AAUAAA, these
proteins cut the RNA transcript free from the
polymerase, releasing the pre-mRNA.
