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By the end of this section, you will be able to:
  • Discuss the similarities and differences between DNA replication in eukaryotes and prokaryotes
  • State the role of telomerase in DNA replication

Eukaryotic genomes are much more complex and larger in size than prokaryotic genomes. The human genome has three billion base pairs per haploid set of chromosomes, and 6 billion base pairs are replicated during the S phase of the cell cycle. There are multiple origins of replication on the eukaryotic chromosome; humans can have up to 100,000 origins of replication. The rate of replication is approximately 100 nucleotides per second, much slower than prokaryotic replication. In yeast, which is a eukaryote, special sequences known as Autonomously Replicating Sequences (ARS) are found on the chromosomes. These are equivalent to the origin of replication in E. coli .

The number of DNA polymerases in eukaryotes is much more than prokaryotes: 14 are known, of which five are known to have major roles during replication and have been well studied. They are known as pol α , pol β , pol γ , pol δ , and pol ε .

The essential steps of replication are the same as in prokaryotes. Before replication can start, the DNA has to be made available as template. Eukaryotic DNA is bound to basic proteins known as histones to form structures called nucleosomes. The chromatin (the complex between DNA and proteins) may undergo some chemical modifications, so that the DNA may be able to slide off the proteins or be accessible to the enzymes of the DNA replication machinery. At the origin of replication, a pre-replication complex is made with other initiator proteins. Other proteins are then recruited to start the replication process ( [link] ).

A helicase using the energy from ATP hydrolysis opens up the DNA helix. Replication forks are formed at each replication origin as the DNA unwinds. The opening of the double helix causes over-winding, or supercoiling, in the DNA ahead of the replication fork. These are resolved with the action of topoisomerases. Primers are formed by the enzyme primase, and using the primer, DNA pol can start synthesis. While the leading strand is continuously synthesized by the enzyme pol δ , the lagging strand is synthesized by pol ε . A sliding clamp protein known as PCNA (Proliferating Cell Nuclear Antigen) holds the DNA pol in place so that it does not slide off the DNA. RNase H removes the RNA primer, which is then replaced with DNA nucleotides. The Okazaki fragments in the lagging strand are joined together after the replacement of the RNA primers with DNA. The gaps that remain are sealed by DNA ligase, which forms the phosphodiester bond.

Telomere replication

Unlike prokaryotic chromosomes, eukaryotic chromosomes are linear. As you’ve learned, the enzyme DNA pol can add nucleotides only in the 5' to 3' direction. In the leading strand, synthesis continues until the end of the chromosome is reached. On the lagging strand, DNA is synthesized in short stretches, each of which is initiated by a separate primer. When the replication fork reaches the end of the linear chromosome, there is no place for a primer to be made for the DNA fragment to be copied at the end of the chromosome. These ends thus remain unpaired, and over time these ends may get progressively shorter as cells continue to divide.

Questions & Answers

there are 3 trimester in human pregnancy
I don't know answer of this question can u help me
what is a cell
Fatima Reply
what is genetic
Janet Reply
I join
what are the branchas of biology
Prisca Reply
zoology, ecology
genetics, microbiology,botany and embryology
what is a cell
Kulunbawi Reply
cell is smallest unit of life. cells are often cell the building blocks of life...
the first twenty element
Orapinega Reply
what are the characteristics of living things?
growth,respiration,nutrition,sensitivity, movement,irritability, excretion,death.
What is the difference between adaptation and competition in animals
Adeyemi Reply
What is biology
it is a natural science stadey about living things
Biology is the bronch of science which deals with the study of life is called biology
what is the x in 300 stands for?
Ogbudu Reply
the properties of life
Clarinda Reply
response to the environment, reproduction, homeostasis, growth,energy processing etc.....
what is reproduction
Reproduction is a fundamental feature of all known life,each individual organism exist as a result of re production.....or else Multiplying...
a complete virus particle known as
Darlington Reply
These are formed from identical protein subunitscalled capsomeres.
fabace family plant name
Pushpam Reply
in eukaryotes ...protein channel name which transport protein ...
Pushpam Reply
in bacteria ...chromosomal dna duplicate structure called
what is a prokaryotic cell and a eukaryotic cell
Matilda Reply
There are two types of cells. Eukaryotic and Prokaryotic cells. Prokaryotic cells don't have a nucleus or membrane enclosed organelles (little organs within that cell). They do however carry genetic material but it's not maintained in the nucleus. Prokaryotic cells are also one celled.
Prokaryotic cells are one celled (single celled).
Prokaryotic cells are Bacteria and Archea
Prokaryotic cells are smaller than Eukaryotic cells.
Eukaryotic cells are more complex. They are much bigger than Prokaryotic cells.
Eukaryotic cells have a nucleus and membrane bound organelles.
Eukaryotic cells are animals cells which also includes us.
Eukaryotic cells are also multicellular.
nice explaination
eukaryotic cells are individual cells .. but eukaryotes are multicellular organisms which consist of many different types of eukaryotic cells
also eukaryotic cells have mitochondria. prokaryotic cells do not
in prokaryotes only ribosomes are present... in eukaryotes mitochondria ...glogi bodies ..epidermis .....prokaryotes one envelop but eukaryotes compartment envelop....envelop mean membrane bound organelles......
prokaryotic cell are cells dat have no true nuclei i.e no cell membrane while eukaryotic cell are cell dat have true nuclei i.e have cell membrane
we have 46 pair of somatic cell and 23 pair of chromosomes in our body, pls can someone explain it to me. pls
Matilda Reply
we have 22 pairs of somatic chromosomes and one pair of sex chromosome
we have 23 pairs of chromosomes,22 pairs of somatic and one pair of sex chromosomes
23 chromosomes from dad & 23 chromosomes from mom 23 +23=46 total chromosomes
X & Y chromosomes are called sex cells, the very presence of a Y chromosome means the person is Male.
XX Female XY Male
If a Karyotype has more than 46 Chromosomes then nondisjunction occured. For example, having an extra chromosome 21 will cause Down Syndrome.
in mammal state the different vertebrae and their location in the body
Igbinigie Reply

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