Eukaryotes and Prokaryotes Key Differences in Protein Synthesis

Prokaryotes Prokaryotes lack a nuclear membrane so mRNA molecules do not need to be completely formed before crossing a nuclear membrane Prokaryotes lack a nuclear membrane so mRNA molecules do not need to be completely formed before crossing a nuclear membrane Therefore translation begins immediately Therefore translation begins immediately

Coupled Transcription and Translation The ribosomes are visible along the mRNA translating it into protein immediately upon it being produced The ribosomes are visible along the mRNA translating it into protein immediately upon it being produced

Observe A Immediate translation

Transcription in Prokaryotes Genome is circular Genome is circular Coupled with translation Coupled with translation Lack of introns (non-coding regions) means no excision Lack of introns (non-coding regions) means no excision

Translation in Prokaryotes Ribosomes are smaller Ribosomes are smaller Ribosomes recognize the start of an mRNA transcript by a unique sequence of purine- rich bases (Shine-Dalgarno sequence) Ribosomes recognize the start of an mRNA transcript by a unique sequence of purine- rich bases (Shine-Dalgarno sequence) Commences with tRNA for methionine entering the P site of the ribosome Commences with tRNA for methionine entering the P site of the ribosome The methionine is tagged with a formyl group The methionine is tagged with a formyl group

Eukaryotes Genome is large and arranged in chromosomes Genome is large and arranged in chromosomes Has coding and non-coding regions Has coding and non-coding regions No operons present No operons present Ribosomes are larger and recognise 5’ cap on mRNA as binding site Ribosomes are larger and recognise 5’ cap on mRNA as binding site Translation occurs in cytoplasm Translation occurs in cytoplasm See chart on page 265 for summary See chart on page 265 for summary

Endosymbiotic Relationships Between Organelles and Cells Endosymbiotic means physical and chemical contact between one species and another species living within its body, usually beneficial to one of the species. Endosymbiotic means physical and chemical contact between one species and another species living within its body, usually beneficial to one of the species.

Main Idea Eukaryotic cells may have evolved from an endosymbiotic relationship between the prokaryotic ancestors of mitochondria and host prokaryotic cells Eukaryotic cells may have evolved from an endosymbiotic relationship between the prokaryotic ancestors of mitochondria and host prokaryotic cells

Mitochondria Resemble Prokaryotic Cells Mitochondria have circular genomes Mitochondria have circular genomes Sequences of mitochondrial DNA are similar to genomes of bacterial cells Sequences of mitochondrial DNA are similar to genomes of bacterial cells Mitochondria divide by fission Mitochondria divide by fission Mitochondria possess their own system of DNA synthesis, transcription and translation Mitochondria possess their own system of DNA synthesis, transcription and translation

Evidence from Red Alga A similar relationship has been discovered between a small alga known as a cryptomonad and a structure found within it which is likely derived from a primitive red alga. A similar relationship has been discovered between a small alga known as a cryptomonad and a structure found within it which is likely derived from a primitive red alga. The structure is called a nucleomorph and is a tiny nucleus containing genomic material found within a eukarytoic endosymbiotic structure The structure is called a nucleomorph and is a tiny nucleus containing genomic material found within a eukarytoic endosymbiotic structure

Gene Organization and Chromosome Structure

Chromosomes Chromosomes have protein and DNA – chromatin Chromosomes have protein and DNA – chromatin Histones – every 200 nucleotides the DNA is coiled around a core group of 8 stabilizing proteins Histones – every 200 nucleotides the DNA is coiled around a core group of 8 stabilizing proteins The positively charged proteins are attracted to the negative DNA The positively charged proteins are attracted to the negative DNA

Nucleosome – complex of histones enveloped by coiled DNA

Supercoiling DNA is folded into a higher level of coiling than is already present in nucleosome DNA is folded into a higher level of coiling than is already present in nucleosome

Non-coding DNA More than 95% of human DNA is non- coding More than 95% of human DNA is non- coding Variable number tandum repeats (VNTR’s) Variable number tandum repeats (VNTR’s) Repetitive sequences of DNA that vary among individiuals Repetitive sequences of DNA that vary among individiuals

VNTR’s Vary from Individual to Individual Shown to the left are the chromosomes of two individuals. The first individual has one chromosome with 4 repeated sequences and one chromosome with 6 repeated sequences. The other individual has one chromosome with 3 repeated sequences and one chromosome with 5 repeated sequences. Shown to the left are the chromosomes of two individuals. The first individual has one chromosome with 4 repeated sequences and one chromosome with 6 repeated sequences. The other individual has one chromosome with 3 repeated sequences and one chromosome with 5 repeated sequences.

Telomeres Telomeres are long sequences of repetitive noncoding DNA on the end of chromosomes Telomeres are long sequences of repetitive noncoding DNA on the end of chromosomes Teleomeres protect cells from losing valuable genomic material during DNA replication Teleomeres protect cells from losing valuable genomic material during DNA replication VNTR’s are also found in centromeres VNTR’s are also found in centromeres

Pseudogenes Pseudogenes have a sequence similar to a functioning gene but are never transcribed Pseudogenes have a sequence similar to a functioning gene but are never transcribed Two types of pseudogenes: Two types of pseudogenes: LINE’s long interspersed nuclear elements LINE’s long interspersed nuclear elements SINE’s short interspersed nuclear elements SINE’s short interspersed nuclear elements

SINES and LINES are used to show Evolutionary Relationships (see page 612)

Review Why does translation begin immediately in prokaryotes? Why does translation begin immediately in prokaryotes? They lack a nuclear membrane. They lack a nuclear membrane. What is the genome like in prokaryotes? What is the genome like in prokaryotes? It is circular and lacks non-coding regions. It is circular and lacks non-coding regions. How are ribosomes different in Prokaryotes? How are ribosomes different in Prokaryotes? Ribosomes are smaller and recognize start of mRNA by a unique sequence of purine-rich bases. Ribosomes are smaller and recognize start of mRNA by a unique sequence of purine-rich bases.

Review What is an endosymbiotic relationship? What is an endosymbiotic relationship? It is one in which one species lives within another. It is one in which one species lives within another. How do mitochondria resemble prokaryotic cells? How do mitochondria resemble prokaryotic cells? They have circular genomes, DNA is similar to bacterial cells, can divide, have own system of DNA synthesis. They have circular genomes, DNA is similar to bacterial cells, can divide, have own system of DNA synthesis.

Review What is a histone? What is a histone? A stabilizing protein associated with DNA A stabilizing protein associated with DNA What is a nucleosome? What is a nucleosome? DNA is coiled around 8 stabilizing proteins. DNA is coiled around 8 stabilizing proteins. What is a VNTR? What is a VNTR? A non-coding region filled with repeats. A non-coding region filled with repeats.

Review What are telomeres? What are telomeres? Long sequences of repetitive non-coding DNA at the ends of the chromosomes. Long sequences of repetitive non-coding DNA at the ends of the chromosomes. What is a pseudogene? What is a pseudogene? A nucleotide sequence similar to a functioning gene but one that does not make RNA or protein. A nucleotide sequence similar to a functioning gene but one that does not make RNA or protein.