Cells background information Flashcards Preview

Science > Cells background information > Flashcards

Flashcards in Cells background information Deck (29):

All cells contain the following organelles:

2.Cell Membrane
5.Fluid filled Vacuole(large & permanent in plants)
6.Cell Wall (plants only)


Outline Cell Membranes

THE cell membrane - around the outside of all cells which protects the cell and controls movement of substances in and out of cells.
•Other membranes surround most organelles including the nucleus
•Membranes are composed of a phospholipid bilayer – a type of fat
Cell Wall (Plants Only!)
•Structure around cell membrane.
•It strengthens plant cells and makes them rigid and tough.


Outline of the Nucleus

•Large dark staining region of an animal or plant cell (not in bacteria).
•It contains all the genetic information for the cell (DNA) which is packaged in chromosomes
•The nucleus of any cell contains the genetic information to allow the growth of that cell.
•The genetic information is contained in a substance called DNA
•The DNA is formed into “filing cabinets” called chromosomes.
Deoxyribonucleic Acid


What is a chromosome

A chromosome is a long molecule of DNA contained within the nucleus of a cell.
It carries the genetic information (genes) of an organism.


Outline on the chromosomes

•The chromosomes you inherit determine what you look like and so much more!
•An autosome is a chromosome other than a sex chromosome
•Sex chromosomes are a chromosome involved in sex determination (e.g. X and Y chromosome)
•Sex chromosomes are referred to as heterosomes.
•They are not identical in shape and size. E.g chromosome 23...X Y


Outline on Karyotype

set of all chromosomes from an organism
It can be difficult to count all the chromosomes when they’re all jumbled up, so genetisits like to take a photo and cut each one out.
Then they paste them onto another sheet, arranging them in pairs, from biggest to smallest matching centromere position.
This is ‘karyotyping’.


Steps involved in Removal of chromosome

1.Break cell wall – blender
2.Break cell membrane – detergent
3.Unwrap DNA coils – meat tenderiser
4.Separate DNA from water - Alcohol


Outline on DNA molecules

All living things contain Genetic material (material passed on from one generation to the next) in the form of a nucleic acid.
Nucleic acids are polymers – that is they are made up of repeated units.
Each unit (a monomer) contains:
•A phosphate group
DNA molecules
• A pentose sugar ( a sugar with 5 carbons in it!)
• A nitrogenous base (a molecule with nitrogen in it!)
DNA Monomer (Nucleotide)


Structure of DNA

The phosphate and sugar form string binds called a sugar phosphate backbone
When two nucleoids attach he result is called a base pair
1.Adenine (A) always pairs with Thymine (T).
2.Cytosine (C) always pairs
with Guanine (G).


What is complementary sequence

The sequence on the matching strand is therefore called the Complementary Sequence.


DNA part 2

•Hydrogen bonds between nucleotides can be broken by enzymes
•This “unzips” the DNA strands
•The strand can then be copied into an mRNA molecule (messenger Ribonucleic Acid)
•This is called Transcription


What is mRNA

•Messenger RNA is like a photocopy of DNA
•It is only a SINGLE stranded molecule (not a double helix like DNA)
•It has three bases the same as DNA: A, C & G
•Instead of Thymine (T), it has a nucleotide called Uracil (U).
•mRNA can leave the nucleus and DNA can’t to keep the original coding safe!
Why is this important? - protein synthesis.
•This mRNA then leaves the nucleus and enters the cytoplasm.
•It attaches to a ribosome (protein making machine) and the mRNA is translated into a polypeptide chain which is really just a protein.
•The building blocks of proteins are called AMINO ACIDS
•This process needs help of another molecule called tRNA (t is for TRANSFER) which picks up the amino acids in the cytoplasm and helps join them to the chain being formed at the ribosome


How does the tRNA know which amino acid to bring?

The nucleotide bases on DNA code for individual amino acids in 3 letter words
•When transcribed to mRNA these get called CODONS
•tRNA has matching ANTI-CODONS (remember base pairs) and each different type of tRNA is for a specific amino acid


What is the difference between Transcription & Translation

Transcription is copying DNA to RNA
Translation is where RNA is used to code for proteins!



•Produces TWO cells per division
•New cells have exactly the same number and type of chromosomes as the original
•They are IDENTICAL and have 46 chromosomes each (in humans)
•This is in SOMATIC (normal body) cells



•The process where all the sex cells of the body are reproduced.
•A sex cell is any cell except a somatic cell
•This process produces 4 new daughter cells.
•The new cells have HALF the number of chromosomes as the original cell (23 in humans)
•Each cell will have a different combination of genes
Reproduction 2: Meiosis
•In both MITOSIS & MEIOSIS, the chromosomes duplicate around the centromere.
Reproduction 2: Meiosis
•But now the homologous chromosome pairs are split up into separate sides.
•Now each side has only half the amount of genetic information.
Reproduction 2: Meiosis
The next stage is similar to mitosis.
In this stage the chromatids are split into separate cells.
There are now 4 cells with only half the chromosomes
The result is 4 daughter cells which contain half the genetic information of the parental cell.


What is Interactive meiosis!

•During meiosis the chromosome pairs sort themselves randomly into each new cell.
–This means that there is a 50:50 chance for each one of each pair of chromosomes to go int one of two cells. These then divide again so we end up with FOUR in total
–The randomness increases variation which is why siblings never look the same (except for identical twins!)
We inherit characteristics from our parents
•Each parent passes on 1 copy of each gene to their offspring.


What is heredity

HEREDITY: Characteristics (traits) that can be transmitted from parent to offspring, i.e. characters that are genetically determined


What is a phenotype

Phenotype: A characteristic or trait influenced by the genotype and the environment


Genes as a unit of inheritance

The Genotype is the genetic makeup of an individual.
A Gene is a unit of heredity ; a nucleotide sequence that codes for a particular protein
An Allele is an alternate form of a gene
The position of the gene within a chromosome is called it’s LOCUS

•Homologous chromosomes are the pairs of each chromosome that codes for the same genes.
•1 from dad, 1 from mum
•They have the same genes in
the same locations, known as loci.


How were genes discovered

How was this Discovered?
Mendel suggested that some unknown items living inside living things controlled their inherited features – he called them hereditary factors
We now call these GENES and each member of his pairs of factors are called ALLELES.


What is a genotype

The Genotype is the genetic makeup of an individual


What is the phenotype of an individual

The Phenotype of an individual is:
1.the overall appearance of an organism
2.an observable trait
3.the physical expression of the genotype
4.the phenotype is determined by the relative dominance of the alleles present in the individual AND the effect of the environment



Phenotype: A physical characteristic is known as a phenotype. It is something we can see or feel.
A combination of the genes from each pair of homologous chromosomes is known as the genotype (gene-o-type).
The characteristic results from these interactions is known as the gene’s expression.



Heterozygous genes can compete for superiority.
The allele that overrides the other is said to be dominant (it dominates)
It masks the effect of the recessive (it is hidden)
Punnet diagram


Determining sex

Females are classified as XX and males as XY
The X chromosomes carry many genes while the Y chromosome only carries a few (about 6)
What is the likely ratio of female to male offspring?


Incomplete Dominance & Co-dominance

Sometimes both alleles are expressed in a heterozygote individual
•Incomplete dominance is when both traits are mixed e.g. a red flower and a white flower producing pink offspring
•Co-dominance is when both traits are expressed e.g. Black dog and white dog producing a black and white dog.
Incomplete dominance
• Example: Purebred white carnations x Purebred Red carnations


Blood types

• Many genes (most) have more than two alleles
• ABO blood types is a good example
• Three different alleles exist
• A and B alleles are dominant to ‘o’ and codominant to each other
• What type of blood could you receive in a transfusion?
Blood type
AA or Ao
BB or Bo



Mutations – when things go wrong...
•If DNA is not copied correctly we get changes in the sequence of DNA.
•These changes to the series of As, Ts, Cs and Gs are caused by MUTAGENIC AGENTS
•A change in only one letter can result in a completely different protein being produced, or a different version of the same protein being produced
Mutations are not always bad
–They are the reasons for different eye colour
–They are one of the driving mechanisms of evolution
•Only mutations in the sex cells are inherited