Cell biology Flashcards
are somatic cells diploid or haploid?
diploid and contain two sets of homologous chromosomes
what are somatic cells?
they are all body cells which arent involved in reproduction
what are germline cells?
they are reproductive cells
what can germline cells divide by?
divide by meiosis (to produce haploid gametes e.g sperm/egg cell) or mitosis (to produce more germline cells)
what do somatic cells divide by?
mitosis
haploid cells have how many chromosomes (in a human?)
23 single chromosomes
what is cellular differentiation?
this is the process by which a cell expresses certain genes to produce protein characteristic for that type of cell, this allows a cell to carry out specialised functions
what are the two types of stem cells in mammals?
embryonic and tissue stem cells
what are stem cells?
they are unspecialised somatic cells that can divide to make copies of themselves (self-renew) and to make cells that differentiate into specialised cells of one or more types
what are the two stages of gene expression?
transcription
translation
medical uses of PCR?
diagnosing disease
estimate the risk of disease onset
forensic uses of PCR?
to amplify DNA samples from crime scenes
What is used to confirm a paternity dispute after PCR
gel electrophoresis can be used to confirm
what does PCR stand for?
polymerase chain reaction
steps of PCR?
DNA is heated between 92-98 degrees to separate the DNA strands
it is then cooled to between 50-65 degrees to allow primers to bind target sequences
it is then heated to between 70 and 80 degrees for heat tolerant DNA polymerase to replicate the region of DNA
what is gene expression?
is the process by which specific genes are activated to produce a required protein
are all the genes in a cell expressed?
only a fraction of genes in a cell are expressed
what are the 3 types of RNA needed in transcription and translation
mRNA tRNA and rRNA
what does mRNA do?
mRNA is also known as messenger RNA and is used to carry a copy of the DNA code from the nucleus to the ribosome. type of RNA that makes up ribosomes
function of mRNA?
mRNA is transcribed from DNA in the nucleus and translated into proteins by ribosomes in the cytoplasm
what is codon (mRNA)
each triplet of bases on the mRNA molecule is called a codon and codes for a specific amino acid
why does tRNA fold?
tRNA folds due to complimentary base pairing
DNA replication
process by which a cell makes an identical copy of its DNA
when does DNA replication happen?
at the start of cell division
what does DNA replication ensure?
DNA replication ensures that each daughter cell inherits an identical copy of DNA
Requirements - what do you need to make a new copy of DNA?
- Original DNA template
- Free DNA nucleotides
- DNA polymerase - enzyme that adds new nucleotides to a growing strand of DNA
- Primers - short strands of nucleotides that bind to the 3’ end allowing DNA polymerase to add free nucleotides.
- ATP (from respiration)
what is a primer?
primers are short complimentary strands of nucleotides that allow DNA polymerase to bind.
which way does DNA polymerase add nucleotides in?
3’-5’ direction
what is the effect of the way that DNA polymerase add nucleotides have?
the lagging strand, primers are added one by one into the replication fork as it widens.
what is the DNA fragments joined by?
DNA ligase to form a complete complementary strand
where does the energy in DNA replication come from?
the process requires energy, which is supplied by ATP produced by the cells respiration.
what is a gene?
Gene = unit of genetic code (section of DNA that codes for a specific protein)
how many genes in a cell are expressed at once?
Only a fraction of the genes in a cell are expressed at one time.
what is RNA?
Ribonucleic acid.
qualities of DNA
2 stranded
Deoxyribose sugar
Adenine - Thymine
Cytosine - Guanine
qualities of RNA
Single stranded
Ribose sugar
Adenine - Uracil
Cytosine - Guanine
mRNA function?
carries complementary copy of the genetic code from DNA (nucleus) to ribosomes in the cytoplasm
what type of structure does mRNA have?
linear
rRNA function?
Combined with proteins to make up the structure of a ribosome.
where does transcription happen?
nucleas
where does translation happen?
at ribosome (in the cytoplasm)
stages of transcription
Helicasemoves along the DNA unwinding the strand.
Hydrogen bonds between base pairs break which allows the unzipping of the double helix.
As helicase breaks the bonds, it synthesises a primary transcript of mRNA using RNA nucleotides. These form hydrogen bonds with the exposed DNA strand by complementary base pairing.
The primary transcript of mRNA is processed to produce a mature transcript of mRNA.
The mature mRNA transcript is now ready to leave the nucleus and travel to the ribosome.
alternative splicing
A transcript from a single gene can be alternatively spliced by treating certain introns as exons
a cell can use one gene to produce different proteins depending on age, metabolic needs, health etc.
enzymes
• Optimums - conditions at which an enzyme is most active (temperature/ pH)
• Biological Catalysts - speed up reactions in cells
• Protein
• They have active sites - the region where the substrate (the substance that the enzyme acts on) attaches and the reactions takes place.
• Products - what an enzyme catalysed reaction produces.
• Specific - one enzyme fits one substrate. (lock and key)
Denatured - active site’s shape is changed by extremes of temperature and pH.
what can cause an absence of a functional enzyme?
A mutation may cause the absence of a functional enzyme.
what are enzymes and how do they work?
Enzymes are biological catalysts that speed up rate of chemical reactions by lowering the activation energy
Activation energy
Energy required to initiate a reaction.
mutations
mutations are random, spontaneous, rare changes to DNA sequences
what is DNA?
a substance that encodes the genetic information of heredity in a chemical language
what shape is DNA?
DNA is a very long double stranded molecule in the shape of a double helix
amino acid
unit of polypeptide structure
anticodon
sequence of 3 bases on tRNA that codes of specific amino acid
codon
sequence of three bases on mRNA that codes for a specific amino acid
exon
coding sequence of DNA
tRNA attachment site
site on tRNA molecule to which a specific amnio acid binds.
interactions
chemical attractions and bonding such as hydrogen bonds between amino acids giving proteins their 3D shape
intron
non-coding sequence of DNA
mature transcript
RNA transcript which has been spliced and processed ready for transcription
peptide bond
strong chemical link between amino acids in the structure of a polypeptide
phenotype
a cells physical and chemical state and is determined by the proteins it produces along with environmental factors that can influence the cell
polypeptide
short strand of amino acids
primary transcript
molecule made when DNA is transcribed
ribose
sugar that forms part of RNA nucleotide
RNA splicing
joining of exons following the removal of introns from a primary transcript
start codon
first codon of mRNA transcript translated by a ribosome
stop codon
codon within mRNA that signals termination of translation into proteins
what can mutations result in?
absence of protein production or production of an altered protein
what does single gene mutation involve?
single gene mutation involves the alteration of a DNA nucleotide sequence as a result of substation , insertion or deletion of nucleotides.
example of substitution
replacing adenosine with guanine
insertion example
adding in another guanine
deletion example
deleting cytosine
chromosome
rod-like structure that contains the genetic material of an organism encoded into DNA
deletion of genes
chromosome mutation in which a sequence of genes is lost from a chromosome
deletion of nucleotides
chromosome mutation in which involves removing a nucelotide from a sequence
translocation
chromosome mutation in which part of a chromosome becomes attached to another
substitution
single gene mutation in which one nucleotide is replaced by another
protein
large molecule made up of chains of amino acid (polypeptides) linked by peptide bonds
stages of DNA replication
stage 1: DNA unwinds and unzips (hydrogen bonds between bases are broken)
stage 2: DNA polymerase can only add nucleotides in a 3’ to 5’ direction and therefore adds free nucleotides to the 3’ end which uses complimentary base pairing.
- the leading strand is replicated continuously
- lagging strand is replicated in fragments nucleotides cannot be added to the phosphate (5’) end because DNA polymerase can only add DNA nucleotides in a 5’ to 3’ direction
the lagging strand is therefore synthesised in fragments
the fragments are then sealed together by an enzyme called ligase
stage 3: 2 new strands twist to form a double helix
what do RNA nucleotides contain?
RNA nucleotides contain a ribose sugar, a phosphate and a base
where is tRNA found?
cytoplasm
why is tRNA folded on itself?
due to hydrogen bonds forming between bases
what are tRNA anticodons complimentary with?
mRNA codons
what is the job of tRNA
tRNA pick up specific aminio acids (with its attachment site) in the cytoplasm and carry them to the ribosome
what does the genetic code translate into and what translates it?
mRNA codons and tRNA anticodons translate the genetic code into the correct sequence of amino acids to make a protein
where are introns found?
between the exons
what is cut out from the primary transcript during transcription?
introns are cut out and removed from the primary transcript
what happens to exons during transcription?
exons are spliced together (RNA splicing) to form mRNA with a continuous sequence exons (this is called the mature transcript of RNA)
where does the mature transcript of mRNA move from?
it moves from the nucleus through the cytoplasm and to a ribosome
when does translation begin and end?
translation begins at a start codon and ends at a stop codon
stages of translation
the mRNA molecule (with transcript) travels through the cytoplasm and attaches to the ribosome.
tRNA molecules transport specific amino acids to the ribosome.
Each mRNA codon codes for a specific amino acid.
The first codon of an mRNA molecule is a start codon. This signals the beginning of translation.
The anti-codons and codons match up and form complementary base pairs.
Peptide bonds form between the adjacent amino acids to form the polypeptide (protein).
Used tRNA molecules exit the ribosome and collect another specific amino acid.
The last codon of an mRNA molecule is a stop codon which signals the end of translation.
what are amino acids linked by?
they are linked by peptide bonds to form poly peptides
why do polypeptide chains fold?
they fold to form 3d shape of a protein which is caused by hydrogen bonds and other interactions between individual amino acids
what is a genetic disorder?
a genetic disorder is a condition or disease that is directly related to the individuals genotype
what determines the structure and function of proteins?
the sequence of amino acids determines the structure and function of the protein
do mutation rates vary?
mutation rates vary from gene to gene and species to species
what are mutations increased by?
Mutations can be increased by mutagenic agents (e.g. mustard gas) and various types of radiation (X-Rays, UV light, Gamma Rays)
Missense
result in one amino acid being changed for another, may result in a non-functional protein or it could have little effect
Example: Sickle-cell disease, PKU
Nonsense
result in a premature stop codon being produced so no amino acid is made and translation stops, produces a shorter protein
Example: Duchenne muscular dystrophy (DMD)
Splice-Site
result in some introns being retained and/or some exons not being included in the mature transcript
Example: Beta Thalassemia
what is the genome of an organism?
total genetic material present in an organism
what is the genome made up of?
The genome is made up of genes and other DNA sequences that do not code for proteins
what does genome sequencing involve?
Genomic sequencing involves determining the sequence of nucleotide bases along the DNA
what can genome sequencing be used for?
Genomic sequencing can be used to find out about individual genes and the entire genome
bioinformatics
Bioinformatics is the name given to the fusion of molecular biology, statistical analysis and computer technology to map and analyse DNA sequences
what can be used to identify base sequence?
computer programs can be used to identify base sequences by looking for sequences similar to known genes
what can bioinformatics be used for?
Bioinformatics can be used to investigate evolutionary biology, inheritance and personalised medicine
what is a personal genome sequence?
A personal genome sequence is a complete set of the person’s DNA bases
what is personal medicine based off of?
Personalised medicine is based on an individual’s genome
what is pharmacogenetics?
Pharmacogenetics is the study of the effects of pharmaceutical drugs on the genetically diverse members of the human population it means that medical treatment could be customised to suit an individuals’ exact metabolic requirements using information gained from genomics e.g. the most suitable drug and correct dosage
cancer cells
- cancer cells divide excessively to produce a mass of abnormal cells called a tumor
- tumour cells do not respond to regulatory signals which results in a mass of abnormal cells
- some of these cells may fail to attach to each other, spreading through the body where they form secondary tumours
- metastasis is the spread of cancer from its primary to other places in the body
what can be separated by gel electrophoresis?
macromolecules such as fragments of DNA from a source can be separated by gel electrophoresis
sequence data
information concerning amino acid or nucleotide base sequences of gene or entire human genome
non-coding
sequences of DNA that do not code for proteins including those that are transcribed but not translated and sequences involved in gene regulation
what is a result of alternative RNA splicing?
different proteins can be expressed from one gene as a result of alternative RNA splicing
what is an example of a mutation?
sickle cell disease
what is a protein?
one or more polypeptide chain
what are fragments?
replicated sequences of the lagging strand which are later joined by ligase
antiparallel
paralel strands in DNA that run in opposite directions in terms of chemical polarity
what is gel electrophoresis?
method of for separation of macromolecules such as fragments of DNA based on their size and electrical charge.
what is one way that the expression of a single gene can result in production of different proteins?
alternative RNA splicing
frame-shift
frame-shift causes all of the codons and all the amino acids after the mutation to be changed. this has a major effect on the structure of the protein that is produced
what is the sugar found in dna?
deoxyribose sugar
what sugar is found in rna?
ribose sugar
what do nucleotides link by deoxyribose to phosphates form?
sugar phosphate backbone
what is dna polymerase?
enzyme that adds new nucleotides to a growing strand of dna
what is PCR?
laboratory technique for amplifying specific targer sequences of DNA
what is thermocycling?
cycles of heating and cooling
requirements for PCR
- DNA / original strand
- complementary primers (to start synthesis)
- heat tolerant DNA polymerase (adds nucleotides and is not denatured by high temperatures)
- supply of nucleotides
what are non-medical uses of PCR?
- used to settle paternity disputes
- sample of DNA from crime scenes
what is the DNA produced in PCR used for after?
The DNA produced in PCR is then used in gel electrophoresis
steps of gel electrophoresis?
fragments are stained then placed in a well cut into block of agarose gel. an electrical current is then passed through the gel causing the fragments to move in the gel.
in gel electrophoresis, what fragments move faster?
shorter fragments move faster and pass farther than longer ones.
what is the final position of the fragments indicated by in gel electrophoresis?
the final position of the fragmenrs are indicated by bands of strain in the gel known as a ladder or profile.
what are base pairs held together by?
weak hydrogen bonds
what does the base sequence of DNA form?
the genetic code
which type of stem cell is pluripotent and why?
embryonic stem cells because of how they can differentiate into all types of cells that can make up an individual
which type of stem cell is multipotent and why?
tissue stem cells because they can differentiate into all types of cells found in a particular tissue type
why are embryonic stem cells controversial?
this is because they involves the destruction of an embryo.
diploid
refers to a cell having two matching sets of chromosomes
what is a secondary tumour?
cancer formed from cells transported from a primary tumour
where does genetic information come from?
genetic information is inherited
what is a fragment in DNA replication?
replicated sequences of the lagging strand which are later joined by ligase
what is the benefit of RNA splicing?
The benefit of RNA splicing is that one gene can produce many different proteins as a result of what segments are treated as introns and exons.
what are single gene mutations a result of?
a change to a single gene nucleotide
what are the three types of single gene mutations?
the substitution of one nucleotide with another
the insertion of one or more nucleotides into a DNA sequence
the deletion of one or more nucleotides from a sequence
example of therapeutic use of stem cells?
skin graphs
